CFR / Title 29 / Part 1926 / Sec. 1926.968 Definitions.

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Enclosed space. * * *

Note to the definition of ``Enclosed space''. The Occupational Safety and Health Administration does not consider spaces that are enclosed but not designed for employee entry under normal operating conditions to be enclosed spaces for the purposes of this subpart. Similarly, the Occupational Safety and Health Administration does not consider spaces that are enclosed and that are expected to contain a hazardous atmosphere to be enclosed spaces for the purposes of this subpart. Such spaces meet the definition of permit spaces in subpart AA of this part, and entry into them must conform to that standard.

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Sec. Appendix A to Subpart V of Part 1926 [Reserved] Sec. Appendix B to Subpart V of Part 1926--Working on Exposed Energized

Parts

I. Introduction

Electric utilities design electric power generation, transmission, and distribution installations to meet National Electrical Safety Code (NESC), ANSI C2, requirements. Electric utilities also design transmission and distribution lines to limit line outages as required by system reliability criteria \1\ and to withstand the maximum overvoltages impressed on the system. Conditions such as switching surges, faults, and lightning can cause overvoltages. Electric utilities generally select insulator design and lengths and the clearances to structural parts so as to prevent outages from contaminated line insulation and during storms. Line insulator lengths and structural clearances have, over the years, come closer to the minimum approach distances used by workers. As minimum approach distances and structural clearances converge, it is increasingly important that system designers and system operating and maintenance personnel understand the concepts underlying minimum approach distances.---------------------------------------------------------------------------

\1\ Federal, State, and local regulatory bodies and electric utilities set reliability requirements that limit the number and duration of system outages.---------------------------------------------------------------------------

The information in this appendix will assist employers in complying with the minimum approach-distance requirements contained in Sec. Sec. 1926.960(c)(1) and 1926.964(c). Employers must use the technical criteria and methodology presented in this appendix in establishing minimum approach distances in accordance with Sec. 1926.960(c)(1)(i) and Table V-2 and Table V-7. This appendix provides essential background information and technical criteria for the calculation of the required minimum approach distances for live-line work on electric power generation, transmission, and distribution installations.

Unless an employer is using the maximum transient overvoltages specified in Table V-8 for voltages over 72.5 kilovolts, the employer must use persons knowledgeable in the techniques discussed in this appendix, and competent in the field of electric transmission and distribution system design, to determine the maximum transient overvoltage.

II. General

A. Definitions. The following definitions from Sec. 1926.968 relate to work on or near electric power generation, transmission, and distribution lines and equipment and the electrical hazards they present.

Exposed. . . . Not isolated or guarded.

Guarded. Covered, fenced, enclosed, or otherwise protected, by means of suitable covers or casings, barrier rails or screens, mats, or platforms, designed to minimize the possibility, under normal conditions, of dangerous approach or inadvertent contact by persons or objects.

Note to the definition of ``guarded'': Wires that are insulated, but not otherwise protected, are not guarded.

Insulated. Separated from other conducting surfaces by a dielectric (including air space) offering a high resistance to the passage of current.

Note to the definition of ``insulated'': When any object is said to be insulated, it is understood to be insulated for the conditions to which it normally is subjected. Otherwise, it is, for the purpose of this subpart, uninsulated.

Isolated. Not readily accessible to persons unless special means for access are used.

Statistical sparkover voltage. A transient overvoltage level that produces a 97.72-percent probability of sparkover (that is, two standard deviations above the voltage at which there is a 50-percent probability of sparkover).

Statistical withstand voltage. A transient overvoltage level that produces a 0.14-percent probability of sparkover (that is, three standard deviations below the voltage at which there is a 50-percent probability of sparkover).

B. Installations energized at 50 to 300 volts. The hazards posed by installations energized at 50 to 300 volts are the same as those found in many other workplaces. That is not to say that there is no hazard, but the complexity of electrical protection required does not compare to that required for high-voltage systems. The employee must avoid contact with the exposed parts, and the protective equipment used (such as rubber insulating gloves) must provide insulation for the voltages involved.

C. Exposed energized parts over 300 volts AC. Paragraph (c)(1)(i) of Sec. 1926.960 requires the employer to establish minimum approach distances no less than the distances computed by Table V-2 for ac systems so that employees can work safely without risk of sparkover.\2\---------------------------------------------------------------------------

\2\ Sparkover is a disruptive electric discharge in which an electric arc forms and electric current passes through air.---------------------------------------------------------------------------

Unless the employee is using electrical protective equipment, air is the insulating medium between the employee and energized parts. The distance between the employee and an energized part must be sufficient for the air to withstand the maximum transient overvoltage that can reach the worksite under the working conditions and practices the employee is using. This distance is the minimum air insulation distance, and it is equal to the electrical component of the minimum approach distance.

Normal system design may provide or include a means (such as lightning arrestors) to control maximum anticipated transient overvoltages, or the employer may use temporary devices (portable protective gaps) or measures (such as preventing automatic circuit breaker reclosing) to achieve the same result. Paragraph (c)(1)(ii) of Sec. 1926.960 requires the employer to determine the maximum anticipated per-unit transient overvoltage, phase-to-ground, through an engineering analysis or assume a maximum anticipated per-unit transient overvoltage, phase-to-ground, in accordance with Table V-8, which specifies the following maximums for ac systems:

72.6 to 420.0 kilovolts.................. 3.5 per unit.420.1 to 550.0 kilovolts................. 3.0 per unit.550.1 to 800.0 kilovolts................. 2.5 per unit.

See paragraph IV.A.2, later in this appendix, for additional discussion of maximum transient overvoltages.

D. Types of exposures. Employees working on or near energized electric power generation, transmission, and distribution systems face two kinds of exposures: Phase-to-ground and phase-to-phase. The exposure is phase-to-ground: (1) With respect to an energized part, when the employee is at ground potential or (2) with respect to ground, when an employee is at the potential of the energized part during live-line barehand work. The exposure is phase-to-phase, with respect to an energized part, when an employee is at the potential of another energized part (at a different potential) during live-line barehand work. III. Determination of Minimum Approach Distances for AC Voltages Greater

Than 300 Volts

A. Voltages of 301 to 5,000 volts. Test data generally forms the basis of minimum air insulation distances. The lowest voltage for which sufficient test data exists is 5,000 volts, and these data indicate that the minimum air insulation distance at that voltage is 20 millimeters (1 inch). Because the minimum air insulation distance increases with increasing voltage, and, conversely, decreases with decreasing voltage, an assumed minimum air insulation distance of 20 millimeters will protect against sparkover at voltages of 301 to 5,000 volts. Thus, 20 millimeters is the electrical component of the minimum approach distance for these voltages.

B. Voltages of 5.1 to 72.5 kilovolts. For voltages from 5.1 to 72.5 kilovolts, the Occupational Safety and Health Administration bases the methodology for calculating the electrical component of the minimum approach distance on Institute of Electrical and Electronic Engineers (IEEE) Standard 4-1995, Standard Techniques for High-Voltage Testing. Table 1 lists the critical sparkover distances from that standard as listed in IEEE Std 516-2009, IEEE Guide for Maintenance Methods on Energized Power Lines.

Table 1--Sparkover Distance for Rod-to-Rod Gap------------------------------------------------------------------------

60 Hz rod-to-rod sparkover (kV Gap spacing from IEEE Std 4-1995

peak) (cm)------------------------------------------------------------------------

25 2

36 3

46 4

53 5

60 6

70 8

79 10

86 12

95 14

104 16

112 18

120 20

143 25

167 30

192 35

218 40

243 45

270 50

322 60------------------------------------------------------------------------Source: IEEE Std 516-2009.

To use this table to determine the electrical component of the minimum approach distance, the employer must determine the peak phase-to-ground transient overvoltage and select a gap from the table that corresponds to that voltage as a withstand voltage rather than a critical sparkover voltage. To calculate the electrical component of the minimum approach distance for voltages between 5 and 72.5 kilovolts, use the following procedure:

1. Divide the phase-to-phase voltage by the square root of 3 to convert it to a phase-to-ground voltage.

2. Multiply the phase-to-ground voltage by the square root of 2 to convert the rms value of the voltage to the peak phase-to-ground voltage.

3. Multiply the peak phase-to-ground voltage by the maximum per-unit transient overvoltage, which, for this voltage range, is 3.0, as discussed later in this appendix. This is the maximum phase-to-ground transient overvoltage, which corresponds to the withstand voltage for the relevant exposure.\3\---------------------------------------------------------------------------

\3\ The withstand voltage is the voltage at which sparkover is not likely to occur across a specified distance. It is the voltage taken at the 3[sigma] point below the sparkover voltage, assuming that the sparkover curve follows a normal distribution.---------------------------------------------------------------------------

4. Divide the maximum phase-to-ground transient overvoltage by 0.85 to determine the corresponding critical sparkover voltage. (The critical sparkover voltage is 3 standard deviations (or 15 percent) greater than the withstand voltage.)

5. Determine the electrical component of the minimum approach distance from Table 1 through interpolation.

Table 2 illustrates how to derive the electrical component of the minimum approach distance for voltages from 5.1 to 72.5 kilovolts, before the application of any altitude correction factor, as explained later.

Table 2--Calculating the Electrical Component of MAD--751 V to 72.5 kV----------------------------------------------------------------------------------------------------------------

Maximum system phase-to-phase voltage (kV)

Step ---------------------------------------------------------------

15 36 46 72.5----------------------------------------------------------------------------------------------------------------1. Divide by [radic]3........................... 8.7 20.8 26.6 41.92. Multiply by [radic]2......................... 12.2 29.4 37.6 59.23. Multiply by 3.0.............................. 36.7 88.2 112.7 177.64. Divide by 0.85............................... 43.2 103.7 132.6 208.95. Interpolate from Table 1..................... 3+(7.2/10)*1 14+(8.7/9)*2 20+(12.6/23)*5 35+(16.9/26)*5Electrical component of MAD (cm)................ 3.72 15.93 22.74 38.25----------------------------------------------------------------------------------------------------------------

C. Voltages of 72.6 to 800 kilovolts. For voltages of 72.6 kilovolts to 800 kilovolts, this subpart bases the electrical component of minimum approach distances, before the application of any altitude correction factor, on the following formula:

Equation 1--For voltages of 72.6 kV to 800 kV D = 0.3048(C + a)VL-GT Where: D = Electrical component of the minimum approach distance in air in

meters;C = a correction factor associated with the variation of gap sparkover

with voltage;

a = A factor relating to the saturation of air at system voltages of 345 kilovolts or higher; \4\---------------------------------------------------------------------------

\4\ Test data demonstrates that the saturation factor is greater than 0 at peak voltages of about 630 kilovolts. Systems operating at 345 kilovolts (or maximum system voltages of 362 kilovolts) can have peak maximum transient overvoltages exceeding 630 kilovolts. Table V-2 sets equations for calculating a based on peak voltage.---------------------------------------------------------------------------

VL-G = Maximum system line-to-ground rms voltage in kilovolts--it should be the ``actual'' maximum, or the normal highest voltage for the range (for example, 10 percent above the nominal voltage); andT = Maximum transient overvoltage factor in per unit.

In Equation 1, C is 0.01: (1) For phase-to-ground exposures that the employer can demonstrate consist only of air across the approach distance (gap) and (2) for phase-to-phase exposures if the employer can demonstrate that no insulated tool spans the gap and that no large conductive object is in the gap. Otherwise, C is 0.011.

In Equation 1, the term a varies depending on whether the employee's exposure is phase-to-ground or phase-to-phase and on whether objects are in the gap. The employer must use the equations in Table 3 to calculate a. Sparkover test data with insulation spanning the gap form the basis for the equations for phase-to-ground exposures, and sparkover test data with only air in the gap form the basis for the equations for phase-to-phase exposures. The phase-to-ground equations result in slightly higher values of a, and, consequently, produce larger minimum approach distances, than the phase-to-phase equations for the same value of VPeak.[GRAPHIC] [TIFF OMITTED] TR11AP14.036

In Equation 1, T is the maximum transient overvoltage factor in per unit. As noted earlier, Sec. 1926.960(c)(1)(ii) requires the employer to determine the maximum anticipated per-unit transient overvoltage, phase-to-ground, through an engineering analysis or assume a maximum anticipated per-unit transient overvoltage, phase-to-ground, in accordance with Table V-8. For phase-to-ground exposures, the employer uses this value, called TL-G, as T in Equation 1. IEEE Std 516-2009 provides the following formula to calculate the phase-to-phase maximum transient overvoltage, TL-L, from TL-G: TL-L = 1.35TL-G + 0.45. For phase-to-phase exposures, the employer uses this value as T in Equation 1.

D. Provisions for inadvertent movement. The minimum approach distance must include an ``adder'' to compensate for the inadvertent movement of the worker relative to an energized part or the movement of the part relative to the worker. This ``adder'' must account for this possible inadvertent movement and provide the worker with a comfortable and safe zone in which to work. Employers must add the distance for inadvertent movement (called the ``ergonomic component of the minimum approach distance'') to the electrical component to determine the total safe minimum approach distances used in live-line work.

The Occupational Safety and Health Administration based the ergonomic component of the minimum approach distance on response time-distance analysis. This technique uses an estimate of the total response time to a hazardous incident and converts that time to the distance traveled. For example, the driver of a car takes a given amount of time to respond to a ``stimulus'' and stop the vehicle. The elapsed time involved results in the car's traveling some distance before coming to a complete stop. This distance depends on the speed of the car at the time the stimulus appears and the reaction time of the driver.

In the case of live-line work, the employee must first perceive that he or she is approaching the danger zone. Then, the worker responds to the danger and must decelerate and stop all motion toward the energized part. During the time it takes to stop, the employee will travel some distance. This is the distance the employer must add to the electrical component of the minimum approach distance to obtain the total safe minimum approach distance.

At voltages from 751 volts to 72.5 kilovolts,\5\ the electrical component of the minimum approach distance is smaller than the ergonomic component. At 72.5 kilovolts, the electrical component is only a little more than 0.3 meters (1 foot). An ergonomic component of the minimum approach distance must provide for all the worker's unanticipated movements. At these voltages, workers generally use rubber insulating gloves; however, these gloves protect only a worker's hands and arms. Therefore, the energized object must be at a safe approach distance to protect the worker's face. In this case, 0.61 meters (2 feet) is a sufficient and practical ergonomic component of the minimum approach distance.---------------------------------------------------------------------------

\5\ For voltages of 50 to 300 volts, Table V-2 specifies a minimum approach distance of ``avoid contact.'' The minimum approach distance for this voltage range contains neither an electrical component nor an ergonomic component.---------------------------------------------------------------------------

For voltages between 72.6 and 800 kilovolts, employees must use different work practices during energized line work. Generally, employees use live-line tools (hot sticks) to perform work on energized equipment. These tools, by design, keep the energized part at a constant distance from the employee and, thus, maintain the appropriate minimum approach distance automatically.

The location of the worker and the type of work methods the worker is using also influence the length of the ergonomic component of the minimum approach distance. In this higher voltage range, the employees use work methods that more tightly control their movements than when the workers perform work using rubber insulating gloves. The worker, therefore, is farther from the energized line or equipment and must be more precise in his or her movements just to perform the work. For these reasons, this subpart adopts an ergonomic component of the minimum approach distance of 0.31 m (1 foot) for voltages between 72.6 and 800 kilovolts.

Table 4 summarizes the ergonomic component of the minimum approach distance for various voltage ranges.

Table 4--Ergonomic Component of Minimum Approach Distance------------------------------------------------------------------------

Distance

Voltage range (kV) -----------------------------------

m ft------------------------------------------------------------------------0.301 to 0.750...................... 0.31 1.00.751 to 72.5....................... 0.61 2.072.6 to 800......................... 0.31 1.0------------------------------------------------------------------------Note: The employer must add this distance to the electrical component of

the minimum approach distance to obtain the full minimum approach

distance.

The ergonomic component of the minimum approach distance accounts for errors in maintaining the minimum approach distance (which might occur, for example, if an employee misjudges the length of a conductive object he or she is holding), and for errors in judging the minimum approach distance. The ergonomic component also accounts for inadvertent movements by the employee, such as slipping. In contrast, the working position selected to properly maintain the minimum approach distance must account for all of an employee's reasonably likely movements and still permit the employee to adhere to the applicable minimum approach distance. (See Figure 1.) Reasonably likely movements include an employee's adjustments to tools, equipment, and working positions and all movements needed to perform the work. For example, the employee should be able to perform all of the following actions without straying into the minimum approach distance:

Adjust his or her hardhat,

maneuver a tool onto an energized part with a reasonable amount of overreaching or underreaching,

reach for and handle tools, material, and equipment passed to him or her, and

adjust tools, and replace components on them, when necessary during the work procedure.

The training of qualified employees required under Sec. 1926.950, and the job planning and briefing required under Sec. 1926.952, must address selection of a proper working position.[GRAPHIC] [TIFF OMITTED] TR11AP14.037

E. Miscellaneous correction factors. Changes in the air medium that forms the insulation influences the strength of an air gap. A brief discussion of each factor follows.

1. Dielectric strength of air. The dielectric strength of air in a uniform electric field at standard atmospheric conditions is approximately 3 kilovolts per millimeter.\6\ The pressure, temperature, and humidity of the air, the shape, dimensions, and separation of the electrodes, and the characteristics of the applied voltage (wave shape) affect the disruptive gradient.---------------------------------------------------------------------------

\6\ For the purposes of estimating arc length, Subpart V generally assumes a more conservative dielectric strength of 10 kilovolts per 25.4 millimeters, consistent with assumptions made in consensus standards such as the National Electrical Safety Code (IEEE C2-2012). The more conservative value accounts for variables such as electrode shape, wave shape, and a certain amount of overvoltage.---------------------------------------------------------------------------

2. Atmospheric effect. The empirically determined electrical strength of a given gap is normally applicable at standard atmospheric conditions (20 [deg]C, 101.3 kilopascals, 11 grams/cubic centimeter humidity). An increase in the density (humidity) of the air inhibits sparkover for a given air gap. The combination of temperature and air pressure that results in the lowest gap sparkover voltage is high temperature and low pressure. This combination of conditions is not likely to occur. Low air pressure, generally associated with high humidity, causes increased electrical strength. An average air pressure generally correlates with low humidity. Hot and dry working conditions normally result in reduced electrical strength. The equations for minimum approach distances in Table V-2 assume standard atmospheric conditions.

3. Altitude. The reduced air pressure at high altitudes causes a reduction in the electrical strength of an air gap. An employer must increase the minimum approach distance by about 3 percent per 300 meters (1,000 feet) of increased altitude for altitudes above 900 meters (3,000 feet). Table V-4 specifies the altitude correction factor that the employer must use in calculating minimum approach distances.

IV. Determining Minimum Approach Distances

A. Factors Affecting Voltage Stress at the Worksite

1. System voltage (nominal). The nominal system voltage range determines the voltage for purposes of calculating minimum approach distances. The employer selects the range in which the nominal system voltage falls, as given in the relevant table, and uses the highest value within that range in per-unit calculations.

2. Transient overvoltages. Operation of switches or circuit breakers, a fault on a line or circuit or on an adjacent circuit, and similar activities may generate transient overvoltages on an electrical system. Each overvoltage has an associated transient voltage wave shape. The wave shape arriving at the site and its magnitude vary considerably.

In developing requirements for minimum approach distances, the Occupational Safety and Health Administration considered the most common wave shapes and the magnitude of transient overvoltages found on electric power generation, transmission, and distribution systems. The equations in Table V-2 for minimum approach distances use per-unit maximum transient overvoltages, which are relative to the nominal maximum voltage of the system. For example, a maximum transient overvoltage value of 3.0 per unit indicates that the highest transient overvoltage is 3.0 times the nominal maximum system voltage.

3. Typical magnitude of overvoltages. Table 5 lists the magnitude of typical transient overvoltages.

Table 5--Magnitude of Typical Transient Overvoltages------------------------------------------------------------------------

Magnitude

Cause (per unit)------------------------------------------------------------------------Energized 200-mile line without closing resistors........... 3.5Energized 200-mile line with one-step closing resistor...... 2.1Energized 200-mile line with multistep resistor............. 2.5Reclosing with trapped charge one-step resistor............. 2.2Opening surge with single restrike.......................... 3.0Fault initiation unfaulted phase............................ 2.1Fault initiation adjacent circuit........................... 2.5Fault clearing.............................................. 1.7 to 1.9------------------------------------------------------------------------

4. Standard deviation--air-gap withstand. For each air gap length under the same atmospheric conditions, there is a statistical variation in the breakdown voltage. The probability of breakdown against voltage has a normal (Gaussian) distribution. The standard deviation of this distribution varies with the wave shape, gap geometry, and atmospheric conditions. The withstand voltage of the air gap is three standard deviations (3[sigma]) below the critical sparkover voltage. (The critical sparkover voltage is the crest value of the impulse wave that, under specified conditions, causes sparkover 50 percent of the time. An impulse wave of three standard deviations below this value, that is, the withstand voltage, has a probability of sparkover of approximately 1 in 1,000.)

5. Broken Insulators. Tests show reductions in the insulation strength of insulator strings with broken skirts. Broken units may lose up to 70 percent of their withstand capacity. Because an employer cannot determine the insulating capability of a broken unit without testing it, the employer must consider damaged units in an insulator to have no insulating value. Additionally, the presence of a live-line tool alongside an insulator string with broken units may further reduce the overall insulating strength. The number of good units that must be present in a string for it to be ``insulated'' as defined by Sec. 1926.968 depends on the maximum overvoltage possible at the worksite.

B. Minimum Approach Distances Based on Known, Maximum-Anticipated Per-

Unit Transient Overvoltages

1. Determining the minimum approach distance for AC systems. Under Sec. 1926.960(c)(1)(ii), the employer must determine the maximum anticipated per-unit transient overvoltage, phase-to-ground, through an engineering analysis or must assume a maximum anticipated per-unit transient overvoltage, phase-to-ground, in accordance with Table V-8. When the employer conducts an engineering analysis of the system and determines that the maximum transient overvoltage is lower than specified by Table V-8, the employer must ensure that any conditions assumed in the analysis, for example, that employees block reclosing on a circuit or install portable protective gaps, are present during energized work. To ensure that these conditions are present, the employer may need to institute new live-work procedures reflecting the conditions and limitations set by the engineering analysis.

2. Calculation of reduced approach distance values. An employer may take the following steps to reduce minimum approach distances when the maximum transient overvoltage on the system (that is, the maximum transient overvoltage without additional steps to control overvoltages) produces unacceptably large minimum approach distances:

Step 1. Determine the maximum voltage (with respect to a given nominal voltage range) for the energized part.

Step 2. Determine the technique to use to control the maximum transient overvoltage. (See paragraphs IV.C and IV.D of this appendix.) Determine the maximum transient overvoltage that can exist at the worksite with that form of control in place and with a confidence level of 3[sigma] . This voltage is the withstand voltage for the purpose of calculating the appropriate minimum approach distance.

Step 3. Direct employees to implement procedures to ensure that the control technique is in effect during the course of the work.

Step 4. Using the new value of transient overvoltage in per unit, calculate the required minimum approach distance from Table V-2. C. Methods of Controlling Possible Transient Overvoltage Stress Found on

a System

1. Introduction. There are several means of controlling overvoltages that occur on transmission systems. For example, the employer can modify the operation of circuit breakers or other switching devices to reduce switching transient overvoltages. Alternatively, the employer can hold the overvoltage to an acceptable level by installing surge arresters or portable protective gaps on the system. In addition, the employer can change the transmission system to minimize the effect of switching operations. Section 4.8 of IEEE Std 516-2009 describes various ways of controlling, and thereby reducing, maximum transient overvoltages.

2. Operation of circuit breakers.\7\ The maximum transient overvoltage that can reach the worksite is often the result of switching on the line on which employees are working. Disabling automatic reclosing during energized line work, so that the line will not be reenergized after being opened for any reason, limits the maximum switching surge overvoltage to the larger of the opening surge or the greatest possible fault-generated surge, provided that the devices (for example, insertion resistors) are operable and will function to limit the transient overvoltage and that circuit breaker restrikes do not occur. The employer must ensure the proper functioning of insertion resistors and other overvoltage-limiting devices when the employer's engineering analysis assumes their proper operation to limit the overvoltage level. If the employer cannot disable the reclosing feature (because of system operating conditions), other methods of controlling the switching surge level may be necessary.---------------------------------------------------------------------------

\7\ The detailed design of a circuit interrupter, such as the design of the contacts, resistor insertion, and breaker timing control, are beyond the scope of this appendix. The design of the system generally accounts for these features. This appendix only discusses features that can limit the maximum switching transient overvoltage on a system.---------------------------------------------------------------------------

Transient surges on an adjacent line, particularly for double circuit construction, may cause a significant overvoltage on the line on which employees are working. The employer's engineering analysis must account for coupling to adjacent lines.

3. Surge arresters. The use of modern surge arresters allows a reduction in the basic impulse-insulation levels of much transmission system equipment. The primary function of early arresters was to protect the system insulation from the effects of lightning. Modern arresters not only dissipate lightning-caused transients, but may also control many other system transients caused by switching or faults.

The employer may use properly designed arresters to control transient overvoltages along a transmission line and thereby reduce the requisite length of the insulator string and possibly the maximum transient overvoltage on the line.\8\---------------------------------------------------------------------------

\8\ Surge arrester application is beyond the scope of this appendix. However, if the employer installs the arrester near the work site, the application would be similar to the protective gaps discussed in paragraph IV.D of this appendix.---------------------------------------------------------------------------

4. Switching Restrictions. Another form of overvoltage control involves establishing switching restrictions, whereby the employer prohibits the operation of circuit breakers until certain system conditions are present. The employer restricts switching by using a tagging system, similar to that used for a permit, except that the common term used for this activity is a ``hold-off'' or ``restriction.'' These terms indicate that the restriction does not prevent operation, but only modifies the operation during the live-work activity.

D. Minimum Approach Distance Based on Control of Maximum Transient

Overvoltage at the Worksite

When the employer institutes control of maximum transient overvoltage at the worksite by installing portable protective gaps, the employer may calculate the minimum approach distance as follows:

Step 1. Select the appropriate withstand voltage for the protective gap based on system requirements and an acceptable probability of gap sparkover.\9\---------------------------------------------------------------------------

\9\ The employer should check the withstand voltage to ensure that it results in a probability of gap flashover that is acceptable from a system outage perspective. (In other words, a gap sparkover will produce a system outage. The employer should determine whether such an outage will impact overall system performance to an acceptable degree.) In general, the withstand voltage should be at least 1.25 times the maximum crest operating voltage.---------------------------------------------------------------------------

Step 2. Determine a gap distance that provides a withstand voltage \10\ greater than or equal to the one selected in the first step.\11\---------------------------------------------------------------------------

\10\ The manufacturer of the gap provides, based on test data, the critical sparkover voltage for each gap spacing (for example, a critical sparkover voltage of 665 kilovolts for a gap spacing of 1.2 meters). The withstand voltage for the gap is equal to 85 percent of its critical sparkover voltage.

\11\ Switch steps 1 and 2 if the length of the protective gap is known.---------------------------------------------------------------------------

Step 3. Use 110 percent of the gap's critical sparkover voltage to determine the phase-to-ground peak voltage at gap sparkover (VPPG Peak).

Step 4. Determine the maximum transient overvoltage, phase-to-ground, at the worksite from the following formula:[GRAPHIC] [TIFF OMITTED] TR11AP14.038

Step 5. Use this value of T \12\ in the equation in Table V-2 to obtain the minimum approach distance. If the worksite is no more than 900 meters (3,000 feet) above sea level, the employer may use this value of T to determine the minimum approach distance from Table 7 through Table 14.---------------------------------------------------------------------------

\12\ IEEE Std 516-2009 states that most employers add 0.2 to the calculated value of T as an additional safety factor.

Note: All rounding must be to the next higher value (that is, always ---------------------------------------------------------------------------round up).

Sample protective gap calculations.

Problem: Employees are to perform work on a 500-kilovolt transmission line at sea level that is subject to transient overvoltages of 2.4 p.u. The maximum operating voltage of the line is 550 kilovolts. Determine the length of the protective gap that will provide the minimum practical safe approach distance. Also, determine what that minimum approach distance is.

Step 1. Calculate the smallest practical maximum transient overvoltage (1.25 times the crest phase-to-ground voltage): \13\---------------------------------------------------------------------------

\13\ To eliminate sparkovers due to minor system disturbances, the employer should use a withstand voltage no lower than 1.25 p.u. Note that this is a practical, or operational, consideration only. It may be feasible for the employer to use lower values of withstand voltage. --------------------------------------------------------------------------- [GRAPHIC] [TIFF OMITTED] TR11AP14.039 This value equals the withstand voltage of the protective gap.

Step 2. Using test data for a particular protective gap, select a gap that has a critical sparkover voltage greater than or equal to: 561kV / 0.85 = 660kV For example, if a protective gap with a 1.22-m (4.0-foot) spacing tested to a critical sparkover voltage of 665 kilovolts (crest), select this gap spacing.

Step 3. The phase-to-ground peak voltage at gap sparkover (VPPG Peak) is 110 percent of the value from the previous step: 665kVx 1.10 = 732kV This value corresponds to the withstand voltage of the electrical component of the minimum approach distance.

Step 4. Use this voltage to determine the worksite value of T:

[GRAPHIC] [TIFF OMITTED] TR11AP14.040

Step 5. Use this value of T in the equation in Table V-2 to obtain the minimum approach distance, or look up the minimum approach distance in Table 7 through Table 14: MAD = 2.29m(7.6ft)

E. Location of Protective Gaps

1. Adjacent structures. The employer may install the protective gap on a structure adjacent to the worksite, as this practice does not significantly reduce the protection afforded by the gap.

2. Terminal stations. Gaps installed at terminal stations of lines or circuits provide a level of protection; however, that level of protection may not extend throughout the length of the line to the worksite. The use of substation terminal gaps raises the possibility that separate surges could enter the line at opposite ends, each with low enough magnitude to pass the terminal gaps without sparkover. When voltage surges occur simultaneously at each end of a line and travel toward each other, the total voltage on the line at the point where they meet is the arithmetic sum of the two surges. A gap installed within 0.8 km (0.5 mile) of the worksite will protect against such intersecting waves. Engineering studies of a particular line or system may indicate that employers can adequately protect employees by installing gaps at even more distant locations. In any event, unless using the default values for T from Table V-8, the employer must determine T at the worksite.

3. Worksite. If the employer installs protective gaps at the worksite, the gap setting establishes the worksite impulse insulation strength. Lightning strikes as far as 6 miles from the worksite can cause a voltage surge greater than the gap withstand voltage, and a gap sparkover can occur. In addition, the gap can sparkover from overvoltages on the line that exceed the withstand voltage of the gap. Consequently, the employer must protect employees from hazards resulting from any sparkover that could occur.

F. Disabling automatic reclosing. There are two reasons to disable the automatic-reclosing feature of circuit-interrupting devices while employees are performing live-line work:

To prevent reenergization of a circuit faulted during the work, which could create a hazard or result in more serious injuries or damage than the injuries or damage produced by the original fault;

To prevent any transient overvoltage caused by the switching surge that would result if the circuit were reenergized.

However, due to system stability considerations, it may not always be feasible to disable the automatic-reclosing feature.

V. Minimum Approach-Distance Tables

A. Legacy tables. Employers may use the minimum approach distances in Table 6 until March 31, 2015.

Table 6--Minimum Approach Distances Until March 31, 2015----------------------------------------------------------------------------------------------------------------

Phase-to-ground exposure Phase-to-phase exposure

Voltage range phase to phase (kV) ----------------------------------------------------------------

m ft m ft----------------------------------------------------------------------------------------------------------------2.1 to 15.0.................................... 0.64 2.1 0.61 2.015.1 to 35.0................................... 0.71 2.3 0.71 2.335.1 to 46.0................................... 0.76 2.5 0.76 2.546.1 to 72.5................................... 0.91 3.0 0.91 3.072.6 to 121.................................... 1.02 3.3 1.37 4.5138 to 145..................................... 1.07 3.5 1.52 5.0161 to 169..................................... 1.12 3.7 1.68 5.5230 to 242..................................... 1.52 5.0 2.54 8.3345 to 362 *................................... 2.13 7.0 4.06 13.3500 to 552 *................................... 3.35 11.0 6.10 20.0700 to 765 *................................... 4.57 15.0 9.45 31.0----------------------------------------------------------------------------------------------------------------* The minimum approach distance may be the shortest distance between the energized part and the grounded

surface.

B. Alternative minimum approach distances. Employers may use the minimum approach distances in Table 7 through Table 14 provided that the employer follows the notes to those tables.

Table 7--AC Minimum Approach Distances--72.6 to 121.0 kV----------------------------------------------------------------------------------------------------------------

Phase-to-ground exposure Phase-to-phase exposure

T (p.u.) ----------------------------------------------------------------

m ft m ft----------------------------------------------------------------------------------------------------------------1.5............................................ 0.67 2.2 0.84 2.81.6............................................ 0.69 2.3 0.87 2.91.7............................................ 0.71 2.3 0.90 3.01.8............................................ 0.74 2.4 0.93 3.11.9............................................ 0.76 2.5 0.96 3.12.0............................................ 0.78 2.6 0.99 3.22.1............................................ 0.81 2.7 1.01 3.32.2............................................ 0.83 2.7 1.04 3.42.3............................................ 0.85 2.8 1.07 3.52.4............................................ 0.88 2.9 1.10 3.62.5............................................ 0.90 3.0 1.13 3.72.6............................................ 0.92 3.0 1.16 3.82.7............................................ 0.95 3.1 1.19 3.92.8............................................ 0.97 3.2 1.22 4.02.9............................................ 0.99 3.2 1.24 4.13.0............................................ 1.02 3.3 1.27 4.23.1............................................ 1.04 3.4 1.30 4.33.2............................................ 1.06 3.5 1.33 4.43.3............................................ 1.09 3.6 1.36 4.53.4............................................ 1.11 3.6 1.39 4.63.5............................................ 1.13 3.7 1.42 4.7----------------------------------------------------------------------------------------------------------------

Table 8--AC Minimum Approach Distances--121.1 to 145.0 kV----------------------------------------------------------------------------------------------------------------

Phase-to-ground rxposure Phase-to-phase rxposure

T (p.u.) ----------------------------------------------------------------

m ft m ft----------------------------------------------------------------------------------------------------------------1.5............................................ 0.74 2.4 0.95 3.11.6............................................ 0.76 2.5 0.98 3.21.7............................................ 0.79 2.6 1.02 3.31.8............................................ 0.82 2.7 1.05 3.41.9............................................ 0.85 2.8 1.08 3.52.0............................................ 0.88 2.9 1.12 3.72.1............................................ 0.90 3.0 1.15 3.82.2............................................ 0.93 3.1 1.19 3.92.3............................................ 0.96 3.1 1.22 4.02.4............................................ 0.99 3.2 1.26 4.12.5............................................ 1.02 3.3 1.29 4.22.6............................................ 1.04 3.4 1.33 4.42.7............................................ 1.07 3.5 1.36 4.52.8............................................ 1.10 3.6 1.39 4.62.9............................................ 1.13 3.7 1.43 4.73.0............................................ 1.16 3.8 1.46 4.83.1............................................ 1.19 3.9 1.50 4.9

3.2............................................ 1.21 4.0 1.53 5.03.3............................................ 1.24 4.1 1.57 5.23.4............................................ 1.27 4.2 1.60 5.23.5............................................ 1.30 4.3 1.64 5.4----------------------------------------------------------------------------------------------------------------

Table 9--AC Minimum Approach Distances--145.1 to 169.0 kV----------------------------------------------------------------------------------------------------------------

Phase-to-ground exposure Phase-to-phase exposure

T (p.u.) ----------------------------------------------------------------

m ft m ft----------------------------------------------------------------------------------------------------------------1.5............................................ 0.81 2.7 1.05 3.41.6............................................ 0.84 2.8 1.09 3.61.7............................................ 0.87 2.9 1.13 3.71.8............................................ 0.90 3.0 1.17 3.81.9............................................ 0.94 3.1 1.21 4.02.0............................................ 0.97 3.2 1.25 4.12.1............................................ 1.00 3.3 1.29 4.22.2............................................ 1.03 3.4 1.33 4.42.3............................................ 1.07 3.5 1.37 4.52.4............................................ 1.10 3.6 1.41 4.62.5............................................ 1.13 3.7 1.45 4.82.6............................................ 1.17 3.8 1.49 4.92.7............................................ 1.20 3.9 1.53 5.02.8............................................ 1.23 4.0 1.57 5.22.9............................................ 1.26 4.1 1.61 5.33.0............................................ 1.30 4.3 1.65 5.43.1............................................ 1.33 4.4 1.70 5.63.2............................................ 1.36 4.5 1.76 5.83.3............................................ 1.39 4.6 1.82 6.03.4............................................ 1.43 4.7 1.88 6.23.5............................................ 1.46 4.8 1.94 6.4----------------------------------------------------------------------------------------------------------------

Table 10--AC Minimum Approach Distances--169.1 to 242.0 kV----------------------------------------------------------------------------------------------------------------

Phase-to-ground exposure Phase-to-phase exposure

T (p.u.) ----------------------------------------------------------------

m ft m ft----------------------------------------------------------------------------------------------------------------1.5............................................ 1.02 3.3 1.37 4.51.6............................................ 1.06 3.5 1.43 4.71.7............................................ 1.11 3.6 1.48 4.91.8............................................ 1.16 3.8 1.54 5.11.9............................................ 1.21 4.0 1.60 5.22.0............................................ 1.25 4.1 1.66 5.42.1............................................ 1.30 4.3 1.73 5.72.2............................................ 1.35 4.4 1.81 5.92.3............................................ 1.39 4.6 1.90 6.22.4............................................ 1.44 4.7 1.99 6.52.5............................................ 1.49 4.9 2.08 6.82.6............................................ 1.53 5.0 2.17 7.12.7............................................ 1.58 5.2 2.26 7.42.8............................................ 1.63 5.3 2.36 7.72.9............................................ 1.67 5.5 2.45 8.03.0............................................ 1.72 5.6 2.55 8.43.1............................................ 1.77 5.8 2.65 8.73.2............................................ 1.81 5.9 2.76 9.13.3............................................ 1.88 6.2 2.86 9.43.4............................................ 1.95 6.4 2.97 9.73.5............................................ 2.01 6.6 3.08 10.1----------------------------------------------------------------------------------------------------------------

Table 11--AC Minimum Approach Distances--242.1 to 362.0 kV----------------------------------------------------------------------------------------------------------------

Phase-to-ground exposure Phase-to-phase exposure

T (p.u.) ----------------------------------------------------------------

1.7............................................ 1.51 5.0 2.27 7.41.8............................................ 1.58 5.2 2.41 7.91.9............................................ 1.65 5.4 2.56 8.42.0............................................ 1.72 5.6 2.71 8.92.1............................................ 1.79 5.9 2.87 9.42.2............................................ 1.87 6.1 3.03 9.92.3............................................ 1.97 6.5 3.20 10.52.4............................................ 2.08 6.8 3.37 11.12.5............................................ 2.19 7.2 3.55 11.62.6............................................ 2.29 7.5 3.73 12.22.7............................................ 2.41 7.9 3.91 12.82.8............................................ 2.52 8.3 4.10 13.52.9............................................ 2.64 8.7 4.29 14.13.0............................................ 2.76 9.1 4.49 14.73.1............................................ 2.88 9.4 4.69 15.43.2............................................ 3.01 9.9 4.90 16.13.3............................................ 3.14 10.3 5.11 16.83.4............................................ 3.27 10.7 5.32 17.53.5............................................ 3.41 11.2 5.52 18.1----------------------------------------------------------------------------------------------------------------

Table 12--AC Minimum Approach Distances--362.1 to 420.0 kV----------------------------------------------------------------------------------------------------------------

Phase-to-ground exposure Phase-to-phase exposure

T (p.u.) ----------------------------------------------------------------

m ft m ft----------------------------------------------------------------------------------------------------------------1.5............................................ 1.53 5.0 2.40 7.91.6............................................ 1.62 5.3 2.58 8.51.7............................................ 1.70 5.6 2.75 9.01.8............................................ 1.78 5.8 2.94 9.61.9............................................ 1.88 6.2 3.13 10.32.0............................................ 1.99 6.5 3.33 10.92.1............................................ 2.12 7.0 3.53 11.62.2............................................ 2.24 7.3 3.74 12.32.3............................................ 2.37 7.8 3.95 13.02.4............................................ 2.50 8.2 4.17 13.72.5............................................ 2.64 8.7 4.40 14.42.6............................................ 2.78 9.1 4.63 15.22.7............................................ 2.93 9.6 4.87 16.02.8............................................ 3.07 10.1 5.11 16.82.9............................................ 3.23 10.6 5.36 17.63.0............................................ 3.38 11.1 5.59 18.33.1............................................ 3.55 11.6 5.82 19.13.2............................................ 3.72 12.2 6.07 19.93.3............................................ 3.89 12.8 6.31 20.73.4............................................ 4.07 13.4 6.56 21.53.5............................................ 4.25 13.9 6.81 22.3----------------------------------------------------------------------------------------------------------------

Table 13--AC Minimum Approach Distances--420.1 to 550.0 kV----------------------------------------------------------------------------------------------------------------

Phase-to-ground exposure Phase-to-phase exposure

T (p.u.) ----------------------------------------------------------------

3.0............................................ 5.07 16.6 8.24 27.0----------------------------------------------------------------------------------------------------------------

Table 14--AC Minimum Approach Distances--550.1 to 800.0 kV----------------------------------------------------------------------------------------------------------------

Phase-to-ground exposure Phase-to-phase exposure

T (p.u.) ----------------------------------------------------------------

an engineering analysis, as required by Sec. 1926.960(c)(1)(ii), or assume a maximum anticipated per-unit

transient overvoltage, phase-to-ground, in accordance with Table V-8.2. For phase-to-phase exposures, the employer must demonstrate that no insulated tool spans the gap and that no

large conductive object is in the gap.3. The worksite must be at an elevation of 900 meters (3,000 feet) or less above sea level. [79 FR 20696, Apr. 11, 2014, as amended at 79 FR 56962, Sept. 24, 2014]

Sec. Appendix C to Subpart V of Part 1926--Protection From Hazardous

Differences in Electric Potential

I. Introduction

Current passing through an impedance impresses voltage across that impedance. Even conductors have some, albeit low, value of impedance. Therefore, if a ``grounded'' \1\ object, such as a crane or deenergized and grounded power line, results in a ground fault on a power line, voltage is impressed on that grounded object. The voltage impressed on the grounded object depends largely on the voltage on the line, on the impedance of the faulted conductor, and on the impedance to ``true,'' or ``absolute,'' ground represented by the object. If the impedance of the object causing the fault is relatively large, the voltage impressed on the object is essentially the phase-to-ground system voltage. However, even faults to grounded power lines or to well grounded transmission towers or substation structures (which have relatively low values of impedance to ground) can result in hazardous voltages.\2\ In all cases, the degree of the hazard depends on the magnitude of the current through the employee and the time of exposure. This appendix discusses methods of protecting workers against the possibility that grounded objects, such as cranes and other mechanical equipment, will contact energized power lines and that deenergized and grounded power lines will become accidentally energized.---------------------------------------------------------------------------

\1\ This appendix generally uses the term ``grounded'' only with respect to grounding that the employer intentionally installs, for example, the grounding an employer installs on a deenergized conductor. However, in this case, the term ``grounded'' means connected to earth, regardless of whether or not that connection is intentional.

\2\ Thus, grounding systems for transmission towers and substation structures should be designed to minimize the step and touch potentials involved.---------------------------------------------------------------------------

II. Voltage-Gradient Distribution

A. Voltage-gradient distribution curve. Absolute, or true, ground serves as a reference and always has a voltage of 0 volts above ground potential. Because there is an impedance between a grounding electrode and absolute ground, there will be a voltage difference between the grounding electrode and absolute ground under ground-fault conditions. Voltage dissipates from the grounding electrode (or from the grounding point) and creates a ground potential gradient. The voltage decreases rapidly with increasing distance from the grounding electrode. A voltage drop associated with this dissipation of voltage is a ground potential. Figure 1 is a typical voltage-gradient distribution curve (assuming a uniform soil texture).[GRAPHIC] [TIFF OMITTED] TR11AP14.041

B. Step and touch potentials. Figure 1 also shows that workers are at risk from step and touch potentials. Step potential is the voltage between the feet of a person standing near an energized grounded object (the electrode). In Figure 1, the step potential is equal to the difference in voltage between two points at different distances from the electrode (where the points represent the location of each foot in relation to the electrode). A person could be at risk of injury during a fault simply by standing near the object.

Touch potential is the voltage between the energized grounded object (again, the electrode) and the feet of a person in contact with the object. In Figure 1, the touch potential is equal to the difference in voltage between the electrode (which is at a distance of 0 meters) and a point some distance away from the electrode (where the point represents the location of the feet of the person in contact with the object). The touch potential could be nearly the full voltage across the grounded object if that object is grounded at a point remote from the place where the person is in contact with it. For example, a crane grounded to the system neutral and that contacts an energized line would expose any person in contact with the crane or its uninsulated load line to a touch potential nearly equal to the full fault voltage.

Figure 2 illustrates step and touch potentials. [GRAPHIC] [TIFF OMITTED] TR11AP14.042

III. Protecting Workers From Hazardous Differences in Electrical

Potential

A. Definitions. The following definitions apply to section III of this appendix:

Bond. The electrical interconnection of conductive parts designed to maintain a common electric potential.

Bonding cable (bonding jumper). A cable connected to two conductive parts to bond the parts together.

Cluster bar. A terminal temporarily attached to a structure that provides a means for the attachment and bonding of grounding and bonding cables to the structure.

Ground. A conducting connection between an electric circuit or equipment and the earth, or to some conducting body that serves in place of the earth.

Grounding cable (grounding jumper). A cable connected between a deenergized part and ground. Note that grounding cables carry fault current and bonding cables generally do not. A cable that bonds two conductive parts but carries substantial fault current (for example, a jumper connected between one phase and a grounded phase) is a grounding cable.

Ground mat (grounding grid). A temporarily or permanently installed metallic mat or grating that establishes an equipotential surface and provides connection points for attaching grounds.

B. Analyzing the hazard. The employer can use an engineering analysis of the power system under fault conditions to determine whether hazardous step and touch voltages will develop. The analysis should determine the voltage on all conductive objects in the work area and the amount of time the voltage will be present. Based on the this analysis, the employer can select appropriate measures and protective equipment, including the measures and protective equipment outlined in Section III of this appendix, to protect each employee from hazardous differences in electric potential. For example, from the analysis, the employer will know the voltage remaining on conductive objects after employees install bonding and grounding equipment and will be able to select insulating equipment with an appropriate rating, as described in paragraph III.C.2 of this appendix.

C. Protecting workers on the ground. The employer may use several methods, including equipotential zones, insulating equipment, and restricted work areas, to protect employees on the ground from hazardous differences in electrical potential.

1. An equipotential zone will protect workers within it from hazardous step and touch potentials. (See Figure 3.) Equipotential zones will not, however, protect employees located either wholly or partially outside the protected area. The employer can establish an equipotential zone for workers on the ground, with respect to a grounded object, through the use of a metal mat connected to the grounded object. The employer can use a grounding grid to equalize the voltage within the grid or bond conductive objects in the immediate work area to minimize the potential between the objects and between each object and ground. (Bonding an object outside the work area can increase the touch potential to that object, however.) Section III.D of this appendix discusses equipotential zones for employees working on deenergized and grounded power lines.

2. Insulating equipment, such as rubber gloves, can protect employees handling grounded equipment and conductors from hazardous touch potentials. The insulating equipment must be rated for the highest voltage that can be impressed on the grounded objects under fault conditions (rather than for the full system voltage).

3. Restricting employees from areas where hazardous step or touch potentials could arise can protect employees not directly involved in performing the operation. The employer must ensure that employees on the ground in the vicinity of transmission structures are at a distance where step voltages would be insufficient to cause injury. Employees must not handle grounded conductors or equipment likely to become energized to hazardous voltages unless the employees are within an equipotential zone or protected by insulating equipment. [GRAPHIC] [TIFF OMITTED] TR11AP14.043

D. Protecting employees working on deenergized and grounded power lines. This Section III.D of Appendix C establishes guidelines to help employers comply with requirements in Sec. 1926.962 for using protective grounding to protect employees working on deenergized power lines. Section 1926.962 applies to grounding of transmission and distribution lines and equipment for the purpose of protecting workers. Paragraph (c) of Sec. 1926.962 requires temporary protective grounds to be placed at such locations and arranged in such a manner that the employer can demonstrate will prevent exposure of each employee to hazardous differences in electric potential.\3\ Sections III.D.1 and III.D.2 of this appendix provide guidelines that employers can use in making the demonstration required by Sec. 1926.962(c). Section III.D.1 of this appendix provides guidelines on how the employer can determine whether particular grounding practices expose employees to hazardous differences in electric potential. Section III.D.2 of this appendix describes grounding methods that the employer can use in lieu of an engineering analysis to make the demonstration required by Sec. 1926.962(c). The Occupational Safety and Health Administration will consider employers that comply with the criteria in this appendix as meeting Sec. 1926.962(c).---------------------------------------------------------------------------

\3\ The protective grounding required by Sec. 1926.962 limits to safe values the potential differences between accessible objects in each employee's work environment. Ideally, a protective grounding system would create a true equipotential zone in which every point is at the same electric potential. In practice, current passing through the grounding and bonding elements creates potential differences. If these potential differences are hazardous, the employer may not treat the zone as an equipotential zone.---------------------------------------------------------------------------

Finally, Section III.D.3 of this appendix discusses other safety considerations that will help the employer comply with other requirements in Sec. 1926.962. Following these guidelines will protect workers from hazards that can occur when a deenergized and grounded line becomes energized.

1. Determining safe body current limits. This Section III.D.1 of Appendix C provides guidelines on how an employer can determine whether any differences in electric potential to which workers could be exposed are hazardous as part of the demonstration required by Sec. 1926.962(c).

Institute of Electrical and Electronic Engineers (IEEE) Standard 1048-2003, IEEE Guide for Protective Grounding of Power Lines, provides the following equation for determining the threshold of ventricular fibrillation when the duration of the electric shock is limited:[GRAPHIC] [TIFF OMITTED] TR11AP14.044 where I is the current through the worker's body, and t is the duration of the current in seconds. This equation represents the ventricular fibrillation threshold for 95.5 percent of the adult population with a mass of 50 kilograms (110 pounds) or more. The equation is valid for current durations between 0.0083 to 3.0 seconds.

To use this equation to set safe voltage limits in an equipotential zone around the worker, the employer will need to assume a value for the resistance of the worker's body. IEEE Std 1048-2003 states that ``total body resistance is usually taken as 1000 [Omega] for determining . . . body current limits.'' However, employers should be aware that the impedance of a worker's body can be substantially less than that value. For instance, IEEE Std 1048-2003 reports a minimum hand-to-hand resistance of 610 ohms and an internal body resistance of 500 ohms. The internal resistance of the body better represents the minimum resistance of a worker's body when the skin resistance drops near zero, which occurs, for example, when there are breaks in the worker's skin, for instance, from cuts or from blisters formed as a result of the current from an electric shock, or when the worker is wet at the points of contact.

Employers may use the IEEE Std 1048-2003 equation to determine safe body current limits only if the employer protects workers from hazards associated with involuntary muscle reactions from electric shock (for example, the hazard to a worker from falling as a result of an electric shock). Moreover, the equation applies only when the duration of the electric shock is limited. If the precautions the employer takes, including those required by applicable standards, do not adequately protect employees from hazards associated with involuntary reactions from electric shock, a hazard exists if the induced voltage is sufficient to pass a current of 1 milliampere through a 500-ohm resistor. (The 500-ohm resistor represents the resistance of an employee. The 1-milliampere current is the threshold of perception.) Finally, if the employer protects employees from injury due to involuntary reactions from electric shock, but the duration of the electric shock is unlimited (that is, when the fault current at the work location will be insufficient to trip the devices protecting the circuit), a hazard exists if the resultant current would be more than 6 milliamperes (the recognized let-go threshold for workers \4\).---------------------------------------------------------------------------

\4\ Electric current passing through the body has varying effects depending on the amount of the current. At the let-go threshold, the current overrides a person's control over his or her muscles. At that level, an employee grasping an object will not be able to let go of the object. The let-go threshold varies from person to person; however, the recognized value for workers is 6 milliamperes.---------------------------------------------------------------------------

2. Acceptable methods of grounding for employers that do not perform an engineering determination. The grounding methods presented in this section of this appendix ensure that differences in electric potential are as low as possible and, therefore, meet Sec. 1926.962(c) without an engineering determination of the potential differences. These methods follow two principles: (i) The grounding method must ensure that the circuit opens in the fastest available clearing time, and (ii) the grounding method must ensure that the potential differences between conductive objects in the employee's work area are as low as possible.

Paragraph (c) of Sec. 1926.962 does not require grounding methods to meet the criteria embodied in these principles. Instead, the paragraph requires that protective grounds be ``placed at such locations and arranged in such a manner that the employer can demonstrate will prevent exposure of each employee to hazardous differences in electric potential.'' However, when the employer's grounding practices do not follow these two principles, the employer will need to perform an engineering analysis to make the demonstration required by Sec. 1926.962(c).

i. Ensuring that the circuit opens in the fastest available clearing time. Generally, the higher the fault current, the shorter the clearing times for the same type of fault. Therefore, to ensure the fastest available clearing time, the grounding method must maximize the fault current with a low impedance connection to ground. The employer accomplishes this objective by grounding the circuit conductors to the best ground available at the worksite. Thus, the employer must ground to a grounded system neutral conductor, if one is present. A grounded system neutral has a direct connection to the system ground at the source, resulting in an extremely low impedance to ground. In a substation, the employer may instead ground to the substation grid, which also has an extremely low impedance to the system ground and, typically, is connected to a grounded system neutral when one is present. Remote system grounds, such as pole and tower grounds, have a higher impedance to the system ground than grounded system neutrals and substation grounding grids; however, the employer may use a remote ground when lower impedance grounds are not available. In the absence of a grounded system neutral, substation grid, and remote ground, the employer may use a temporary driven ground at the worksite.

In addition, if employees are working on a three-phase system, the grounding method must short circuit all three phases. Short circuiting all phases will ensure faster clearing and lower the current through the grounding cable connecting the deenergized line to ground, thereby lowering the voltage across that cable. The short circuit need not be at the worksite; however, the employer must treat any conductor that is not grounded at the worksite as energized because the ungrounded conductors will be energized at fault voltage during a fault.

ii. Ensuring that the potential differences between conductive objects in the employee's work area are as low as possible. To achieve as low a voltage as possible across any two conductive objects in the work area, the employer must bond all conductive objects in the work area. This section of this appendix discusses how to create a zone that minimizes differences in electric potential between conductive objects in the work area.

The employer must use bonding cables to bond conductive objects, except for metallic objects bonded through metal-to-metal contact. The employer must ensure that metal-to-metal contacts are tight and free of contamination, such as oxidation, that can increase the impedance across the connection. For example, a bolted connection between metal lattice tower members is acceptable if the connection is tight and free of corrosion and other contamination. Figure 4 shows how to create an equipotential zone for metal lattice towers.

Wood poles are conductive objects. The poles can absorb moisture and conduct electricity, particularly at distribution and transmission voltages. Consequently, the employer must either: (1) Provide a conductive platform, bonded to a grounding cable, on which the worker stands or (2) use cluster bars to bond wood poles to the grounding cable. The employer must ensure that employees install the cluster bar below, and close to, the worker's feet. The inner portion of the wood pole is more conductive than the outer shell, so it is important that the cluster bar be in conductive contact with a metal spike or nail that penetrates the wood to a depth greater than or equal to the depth the worker's climbing gaffs will penetrate the wood. For example, the employer could mount the cluster bar on a bare pole ground wire fastened to the pole with nails or staples that penetrate to the required depth. Alternatively, the employer may temporarily nail a conductive strap to the pole and connect the strap to the cluster bar. Figure 5 shows how to create an equipotential zone for wood poles. [GRAPHIC] [TIFF OMITTED] TR11AP14.045 [GRAPHIC] [TIFF OMITTED] TR11AP14.046

For underground systems, employers commonly install grounds at the points of disconnection of the underground cables. These grounding points are typically remote from the manhole or underground vault where employees will be working on the cable. Workers in contact with a cable grounded at a remote location can experience hazardous potential differences if the cable becomes energized or if a fault occurs on a different, but nearby, energized cable. The fault current causes potential gradients in the earth, and a potential difference will exist between the earth where the worker is standing and the earth where the cable is grounded. Consequently, to create an equipotential zone for the worker, the employer must provide a means of connecting the deenergized cable to ground at the worksite by having the worker stand on a conductive mat bonded to the deenergized cable. If the cable is cut, the employer must install a bond across the opening in the cable or install one bond on each side of the opening to ensure that the separate cable ends are at the same potential. The employer must protect the worker from any hazardous differences in potential any time there is no bond between the mat and the cable (for example, before the worker installs the bonds).

3. Other safety-related considerations. To ensure that the grounding system is safe and effective, the employer should also consider the following factors: \5\---------------------------------------------------------------------------

\5\ This appendix only discusses factors that relate to ensuring an equipotential zone for employees. The employer must consider other factors in selecting a grounding system that is capable of conducting the maximum fault current that could flow at the point of grounding for the time necessary to clear the fault, as required by Sec. 1926.962(d)(1)(i). IEEE Std 1048-2003 contains guidelines for selecting and installing grounding equipment that will meet Sec. 1926.962(d)(1)(i).---------------------------------------------------------------------------

i. Maintenance of grounding equipment. It is essential that the employer properly maintain grounding equipment. Corrosion in the connections between grounding cables and clamps and on the clamp surface can increase the resistance of the cable, thereby increasing potential differences. In addition, the surface to which a clamp attaches, such as a conductor or tower member, must be clean and free of corrosion and oxidation to ensure a low-resistance connection. Cables must be free of damage that could reduce their current-carrying capacity so that they can carry the full fault current without failure. Each clamp must have a tight connection to the cable to ensure a low resistance and to ensure that the clamp does not separate from the cable during a fault.

ii. Grounding cable length and movement. The electromagnetic forces on grounding cables during a fault increase with increasing cable length. These forces can cause the cable to move violently during a fault and can be high enough to damage the cable or clamps and cause the cable to fail. In addition, flying cables can injure workers. Consequently, cable lengths should be as short as possible, and grounding cables that might carry high fault current should be in positions where the cables will not injure workers during a fault.

Sec. Appendix D to Subpart V of Part 1926--Methods of Inspecting and

Testing Wood Poles

I. Introduction

When employees are to perform work on a wood pole, it is important to determine the condition of the pole before employees climb it. The weight of the employee, the weight of equipment to be installed, and other working stresses (such as the removal or retensioning of conductors) can lead to the failure of a defective pole or a pole that is not designed to handle the additional stresses.\1\ For these reasons, it is essential that, before an employee climbs a wood pole, the employer ascertain that the pole is capable of sustaining the stresses of the work. The determination that the pole is capable of sustaining these stresses includes an inspection of the condition of the pole.---------------------------------------------------------------------------

\1\ A properly guyed pole in good condition should, at a minimum, be able to handle the weight of an employee climbing it.---------------------------------------------------------------------------

If the employer finds the pole to be unsafe to climb or to work from, the employer must secure the pole so that it does not fail while an employee is on it. The employer can secure the pole by a line truck boom, by ropes or guys, or by lashing a new pole alongside it. If a new one is lashed alongside the defective pole, employees should work from the new one.

II. Inspecting Wood Poles

A qualified employee should inspect wood poles for the following conditions:\2\---------------------------------------------------------------------------

\2\ The presence of any of these conditions is an indication that the pole may not be safe to climb or to work from. The employee performing the inspection must be qualified to make a determination as to whether it is safe to perform the work without taking additional precautions.---------------------------------------------------------------------------

A. General condition. Buckling at the ground line or an unusual angle with respect to the ground may indicate that the pole has rotted or is broken.

B. Cracks. Horizontal cracks perpendicular to the grain of the wood may weaken the pole. Vertical cracks, although not normally considered to be a sign of a defective pole, can pose a hazard to the climber, and the employee should keep his or her gaffs away from them while climbing.

C. Holes. Hollow spots and woodpecker holes can reduce the strength of a wood pole.

D. Shell rot and decay. Rotting and decay are cutout hazards and possible indications of the age and internal condition of the pole.

E. Knots. One large knot or several smaller ones at the same height on the pole may be evidence of a weak point on the pole.

F. Depth of setting. Evidence of the existence of a former ground line substantially above the existing ground level may be an indication that the pole is no longer buried to a sufficient depth.

G. Soil conditions. Soft, wet, or loose soil around the base of the pole may indicate that the pole will not support any change in stress.

H. Burn marks. Burning from transformer failures or conductor faults could damage the pole so that it cannot withstand changes in mechanical stress.

III. Testing Wood Poles

The following tests, which are from Sec. 1910.268(n)(3) of this chapter, are acceptable methods of testing wood poles:

A. Hammer test. Rap the pole sharply with a hammer weighing about 1.4 kg (3 pounds), starting near the ground line and continuing upwards circumferentially around the pole to a height of approximately 1.8 meters (6 feet). The hammer will produce a clear sound and rebound sharply when striking sound wood. Decay pockets will be indicated by a dull sound or a less pronounced hammer rebound. Also, prod the pole as near the ground line as possible using a pole prod or a screwdriver with a blade at least 127 millimeters (5 inches) long. If substantial decay is present, the pole is unsafe.

B. Rocking test. Apply a horizontal force to the pole and attempt to rock it back and forth in a direction perpendicular to the line. Exercise caution to avoid causing power lines to swing together. Apply the force to the pole either by pushing it with a pike pole or pulling the pole with a rope. If the pole cracks during the test, it is unsafe.

Sec. Appendix E to Subpart V of Part 1926--Protection From Flames and

Electric Arcs

I. Introduction

Paragraph (g) of Sec. 1926.960 addresses protecting employees from flames and electric arcs. This paragraph requires employers to: (1) Assess the workplace for flame and electric-arc hazards (paragraph (g)(1)); (2) estimate the available heat energy from electric arcs to which employees would be exposed (paragraph (g)(2)); (3) ensure that employees wear clothing that will not melt, or ignite and continue to burn, when exposed to flames or the estimated heat energy (paragraph (g)(3)); and (4) ensure that employees wear flame-resistant clothing \1\ and protective clothing and other protective equipment that has an arc rating greater than or equal to the available heat energy under certain conditions (paragraphs (g)(4) and (g)(5)). This appendix contains information to help employers estimate available heat energy as required by Sec. 1926.960(g)(2), select protective clothing and other protective equipment with an arc rating suitable for the available heat energy as required by Sec. 1926.960(g)(5), and ensure that employees do not wear flammable clothing that could lead to burn injury as addressed by Sec. Sec. 1926.960(g)(3) and (g)(4).---------------------------------------------------------------------------

\1\ Flame-resistant clothing includes clothing that is inherently flame resistant and clothing chemically treated with a flame retardant. (See ASTM F1506-10a, Standard Performance Specification for Flame Resistant Textile Materials for Wearing Apparel for Use by Electrical Workers Exposed to Momentary Electric Arc and Related Thermal Hazards, and ASTM F1891-12 Standard Specification for Arc and Flame Resistant Rainwear.)---------------------------------------------------------------------------

II. Assessing the Workplace for Flame and Electric-Arc Hazards

Paragraph (g)(1) of Sec. 1926.960 requires the employer to assess the workplace to identify employees exposed to hazards from flames or from electric arcs. This provision ensures that the employer evaluates employee exposure to flames and electric arcs so that employees who face such exposures receive the required protection. The employer must conduct an assessment for each employee who performs work on or near exposed, energized parts of electric circuits.

A. Assessment Guidelines

Sources electric arcs. Consider possible sources of electric arcs, including:

Energized circuit parts not guarded or insulated,

Switching devices that produce electric arcs in normal operation,

Sliding parts that could fault during operation (for example, rack-mounted circuit breakers), and

Energized electric equipment that could fail (for example, electric equipment with damaged insulation or with evidence of arcing or overheating).

Exposure to flames. Identify employees exposed to hazards from flames. Factors to consider include:

The proximity of employees to open flames, and

For flammable material in the work area, whether there is a reasonable likelihood that an electric arc or an open flame can ignite the material.

Probability that an electric arc will occur. Identify employees exposed to electric-arc hazards. The Occupational Safety and Health Administration will consider an employee exposed to electric-arc hazards if there is a reasonable likelihood that an electric arc will occur in the employee's work area, in other words, if the probability of such an event is higher than it is for the normal operation of enclosed equipment. Factors to consider include:

For energized circuit parts not guarded or insulated, whether conductive objects can come too close to or fall onto the energized parts,

For exposed, energized circuit parts, whether the employee is closer to the part than the minimum approach distance established by the employer (as permitted by Sec. 1926.960(c)(1)(iii)).

Whether the operation of electric equipment with sliding parts that could fault during operation is part of the normal operation of the equipment or occurs during servicing or maintenance, and

For energized electric equipment, whether there is evidence of impending failure, such as evidence of arcing or overheating.

B. Examples

Table 1 provides task-based examples of exposure assessments.

Table 1--Example Assessments for Various Tasks----------------------------------------------------------------------------------------------------------------

----------------------------------------------------------------------------------------------------------------

Task Is employee exposed to flame or

electric-arc hazard?--------------------------------------------------------------------------Normal operation of enclosed equipment, The employer properly installs No.

such as closing or opening a switch. and maintains enclosed

equipment, and there is no

evidence of impending failure.

There is evidence of arcing or Yes.

overheating.

Parts of the equipment are Yes.

loose or sticking, or the

equipment otherwise exhibits

signs of lack of maintenance.--------------------------------------------------------------------------Servicing electric equipment, such as racking in a circuit breaker or Yes.

replacing a switch.-----------------------------------------Inspection of electric equipment with The employee is not holding No.

exposed energized parts. conductive objects and remains

outside the minimum approach

distance established by the

employer.

The employee is holding a Yes.

conductive object, such as a

flashlight, that could fall or

otherwise contact energized

parts (irrespective of whether

the employee maintains the

minimum approach distance).

The employee is closer than the Yes.

minimum approach distance

established by the employer

(for example, when wearing

rubber insulating gloves or

rubber insulating gloves and

sleeves).--------------------------------------------------------------------------Using open flames, for example, in wiping cable splice sleeves........... Yes.----------------------------------------------------------------------------------------------------------------

III. Protection Against Burn Injury

A. Estimating Available Heat Energy

Calculation methods. Paragraph (g)(2) of Sec. 1926.960 provides that, for each employee exposed to an electric-arc hazard, the employer must make a reasonable estimate of the heat energy to which the employee would be exposed if an arc occurs. Table 2 lists various methods of calculating values of available heat energy from an electric circuit. The Occupational Safety and Health Administration does not endorse any of these specific methods. Each method requires the input of various parameters, such as fault current, the expected length of the electric arc, the distance from the arc to the employee, and the clearing time for the fault (that is, the time the circuit protective devices take to open the circuit and clear the fault). The employer can precisely determine some of these parameters, such as the fault current and the clearing time, for a given system. The employer will need to estimate other parameters, such as the length of the arc and the distance between the arc and the employee, because such parameters vary widely.

Table 2--Methods of Calculating Incident Heat Energy From an Electric

Arc------------------------------------------------------------------------

-------------------------------------------------------------------------1. Standard for Electrical Safety Requirements for Employee Workplaces,

NFPA 70E-2012, Annex D, ``Sample Calculation of Flash Protection

Boundary.''2. Doughty, T.E., Neal, T.E., and Floyd II, H.L., ``Predicting Incident

Energy to Better Manage the Electric Arc Hazard on 600 V Power

Distribution Systems,'' Record of Conference Papers IEEE IAS 45th

Annual Petroleum and Chemical Industry Conference, September 28--30,

1998.3. Guide for Performing Arc-Flash Hazard Calculations, IEEE Std 1584-

2002, 1584a--2004 (Amendment 1 to IEEE Std 1584-2002), and 1584b-2011

(Amendment 2: Changes to Clause 4 of IEEE Std 1584-2002).*4. ARCPRO, a commercially available software program developed by

Kinectrics, Toronto, ON, CA.*This appendix refers to IEEE Std 1584-2002 with both amendments as IEEE

Std 1584b-2011.------------------------------------------------------------------------

The amount of heat energy calculated by any of the methods is approximatelyinversely proportional to the square of the distance between the employee and the arc. In other words, if the employee is very close to the arc, the heat energy is very high; but if the employee is just a few more centimeters away, the heat energy drops substantially. Thus, estimating the distance from the arc to the employee is key to protecting employees.

The employer must select a method of estimating incident heat energy that provides a reasonable estimate of incident heat energy for the exposure involved. Table 3 shows which methods provide reasonable estimates for various exposures.

Table 3--Selecting a Reasonable Incident-Energy Calculation Method \1\--------------------------------------------------------------------------------------------------------------------------------------------------------

600 V and Less \2\ 601 V to 15 kV \2\ More than 15 kV

Incident-energy calculation method -----------------------------------------------------------------------------------------

1[Phi] 3[Phi]a 3[Phi]b 1[Phi] 3[Phi]a 3[Phi]b 1[Phi] 3[Phi]a 3[Phi]b--------------------------------------------------------------------------------------------------------------------------------------------------------NFPA 70E-2012 Annex D (Lee equation).......................... Y-C Y N Y-C Y-C N N \3\ N \3\ N \3\Doughty, Neal, and Floyd...................................... Y-C Y Y N N N N N NIEEE Std 1584b-2011........................................... Y Y Y Y Y Y N N NARCPRO........................................................ Y N N Y N N Y Y \4\ Y \4\--------------------------------------------------------------------------------------------------------------------------------------------------------Key:1[Phi]: Single-phase arc in open air3[Phi]a: Three-phase arc in open air3[Phi]b: Three-phase arc in an enclosure (box)Y: Acceptable; produces a reasonable estimate of incident heat energy from this type of electric arcN: Not acceptable; does not produce a reasonable estimate of incident heat energy from this type of electric arcY-C: Acceptable; produces a reasonable, but conservative, estimate of incident heat energy from this type of electric arc.Notes:\1\ Although the Occupational Safety and Health Administration will consider these methods reasonable for enforcement purposes when employers use

the methods in accordance with this table, employers should be aware that the listed methods do not necessarily result in estimates that will provide

full protection from internal faults in transformers and similar equipment or from arcs in underground manholes or vaults.\2\ At these voltages, the presumption is that the arc is three-phase unless the employer can demonstrate that only one phase is present or that the

spacing of the phases is sufficient to prevent a multiphase arc from occurring.\3\ Although the Occupational Safety and Health Administration will consider this method acceptable for purposes of assessing whether incident energy

exceeds 2.0 cal/cm\2\, the results at voltages of more than 15 kilovolts are extremely conservative and unrealistic.\4\The Occupational Safety and Health Administration will deem the results of this method reasonable when the employer adjusts them using the conversion

factors for three-phase arcs in open air or in an enclosure, as indicated in the program's instructions.

Selecting a reasonable distance from the employee to the arc. In estimating available heat energy, the employer must make some reasonable assumptions about how far the employee will be from the electric arc. Table 4 lists reasonable distances from the employee to the electric arc. The distances in Table 4 are consistent with national consensus standards, such as the Institute of Electrical and Electronic Engineers' National Electrical Safety Code, ANSI/IEEE C2-2012, and IEEE Guide for Performing Arc-Flash Hazard Calculations, IEEE Std 1584b-2011. The employer is free to use other reasonable distances, but must consider equipment enclosure size and the working distance to the employee in selecting a distance from the employee to the arc. The Occupational Safety and Health Administration will consider a distance reasonable when the employer bases it on equipment size and working distance.

Table 4--Selecting a Reasonable Distance from the Employee to the

Electric Arc------------------------------------------------------------------------

Single-phase arc Three-phase arc mm

Class of equipment mm (inches) (inches)------------------------------------------------------------------------Cable........................... NA*............... 455 (18)Low voltage MCCs and panelboards NA................ 455 (18)Low-voltage switchgear.......... NA................ 610 (24)5-kV switchgear................. NA................ 910 (36)15-kV switchgear................ NA................ 910 (36)Single conductors in air (up to 380 (15).......... NA

46 kilovolts), work with rubber

insulating gloves.Single conductors in air, work MAD-(2xkVx2.54)... NA

with live-line tools and live- (MAD-(2xkV/10))

line barehand work. [dagger].------------------------------------------------------------------------* NA = not applicable.[dagger] The terms in this equation are:MAD = The applicable minimum approach distance, andkV = The system voltage in kilovolts.

Selecting a reasonable arc gap. For a single-phase arc in air, the electric arc will almost always occur when an energized conductor approaches too close to ground. Thus, an employer can determine the arc gap, or arc length, for these exposures by the dielectric strength of air and the voltage on the line. The dielectric strength of air is approximately 10 kilovolts for every 25.4 millimeters (1 inch). For example, at 50 kilovolts, the arc gap would be 50 / 10 x 25.4 (or 50 x 2.54), which equals 127 millimeters (5 inches).

For three-phase arcs in open air and in enclosures, the arc gap will generally be dependent on the spacing between parts energized at different electrical potentials. Documents such as IEEE Std 1584b-2011 provide information on these distances. Employers may select a reasonable arc gap from Table 5, or they may select any other reasonable arc gap based on sparkover distance or on the spacing between (1) live parts at different potentials or (2) live parts and grounded parts (for example, bus or conductor spacings in equipment). In any event, the employer must use an estimate that reasonably resembles the actual exposures faced by the employee.

Table 5--Selecting a Reasonable Arc Gap----------------------------------------------------------------------------------------------------------------

Three-phase arc mm \1\

Class of equipment Single-phase arc mm (inches) (inches)----------------------------------------------------------------------------------------------------------------Cable........................................ NA \2\............................ 13 (0.5)Low voltage MCCs and panelboards............. NA................................ 25 (1.0)Low-voltage switchgear....................... NA................................ 32 (1.25)5-kV switchgear.............................. NA................................ 104 (4.0)15-kV switchgear............................. NA................................ 152 (6.0)Single conductors in air, 15 kV and less..... 51 (2.0).......................... Phase conductor spacings.Single conductor in air, more than 15 kV..... Voltage in kV x 2.54..............

(Voltage in kV x 0.1), but no less Phase conductor spacings.

than 51 mm (2 inches)----------------------------------------------------------------------------------------------------------------\1\ Source: IEEE Std 1584b-2011.\2\ NA = not applicable.

Making estimates over multiple system areas. The employer need not estimate the heat-energy exposure for every job task performed by each employee. Paragraph (g)(2) of Sec. 1926.960 permits the employer to make broad estimates that cover multiple system areas provided that: (1) The employer uses reasonable assumptions about the energy-exposure distribution throughout the system, and (2) the estimates represent the maximum exposure for those areas. For example, the employer can use the maximum fault current and clearing time to cover several system areas at once.

Incident heat energy for single-phase-to-ground exposures. Table 6 and Table 7 provide incident heat energy levels for open-air, phase-to-ground electric-arc exposures typical for overhead systems.\2\ Table 6 presents estimates of available energy for employees using rubber insulating gloves to perform work on overhead systems operating at 4 to 46 kilovolts. The table assumes that the employee will be 380 millimeters (15 inches) from the electric arc, which is a reasonable estimate for rubber insulating glove work. Table 6 also assumes that the arc length equals the sparkover distance for the maximum transient overvoltage of each voltage range.\3\ To use the table, an employer would use the voltage, maximum fault current, and maximum clearing time for a system area and, using the appropriate voltage range and fault-current and clearing-time values corresponding to the next higher values listed in the table, select the appropriate heat energy (4, 5, 8, or 12 cal/cm\2\) from the table. For example, an employer might have a 12,470-volt power line supplying a system area. The power line can supply a maximum fault current of 8 kiloamperes with a maximum clearing time of 10 cycles. For rubber glove work, this system falls in the 4.0-to-15.0-kilovolt range; the next-higher fault current is 10 kA (the second row in that voltage range); and the clearing time is under 18 cycles (the first column to the right of the fault current column). Thus, the available heat energy for this part of the system will be 4 cal/cm\2\ or less (from the column heading), and the employer could select protection with a 5-cal/cm\2\ rating to meet Sec. 1926.960(g)(5). Alternatively, an employer could select a base incident-energy value and ensure that the clearing times for each voltage range and fault current listed in the table do not exceed the corresponding clearing time specified in the table. For example, an employer that provides employees with arc-flash protective equipment rated at 8 cal/cm\2\ can use the table to determine if any system area exceeds 8 cal/cm\2\ by checking the clearing time for the highest fault current for each voltage range and ensuring that the clearing times do not exceed the values specified in the 8-cal/cm\2\ column in the table.---------------------------------------------------------------------------

\2\ The Occupational Safety and Health Administration used metric values to calculate the clearing times in Table 6 and Table 7. An employer may use English units to calculate clearing times instead even though the results will differ slightly.

\3\ The Occupational Safety and Health Administration based this assumption, which is more conservative than the arc length specified in Table 5, on Table 410-2 of the 2012 NESC.---------------------------------------------------------------------------

Table 7 presents similar estimates for employees using live-line tools to perform work on overhead systems operating at voltages of 4 to 800 kilovolts. The table assumes that the arc length will be equal to the sparkover distance \4\ and that the employee will be a distance from the arc equal to the minimum approach distance minus twice the sparkover distance.---------------------------------------------------------------------------

\4\ The dielectric strength of air is about 10 kilovolts for every 25.4 millimeters (1 inch). Thus, the employer can estimate the arc length in millimeters to be the phase-to-ground voltage in kilovolts multiplied by 2.54 (or voltage (in kilovolts) x 2.54).---------------------------------------------------------------------------

The employer will need to use other methods for estimating available heat energy in situations not addressed by Table 6 or Table 7. The calculation methods listed in Table 2 and the guidance provided in Table 3 will help employers do this. For example, employers can use IEEE Std 1584b-2011 to estimate the available heat energy (and to select appropriate protective equipment) for many specific conditions, including lower-voltage, phase-to-phase arc, and enclosed arc exposures. Table 6--Incident Heat Energy for Various Fault Currents, Clearing Times, and Voltages of 4.0 to 46.0 kV: Rubber

Insulating Glove Exposures Involving Phase-to-Ground Arcs in Open Air Only * [dagger] [Dagger]----------------------------------------------------------------------------------------------------------------

Maximum clearing time (cycles)

Voltage range (kV) ** Fault current ---------------------------------------------------------------

(kA) 4 cal/cm\2\ 5 cal/cm\2\ 8 cal/cm\2\ 12 cal/cm\2\----------------------------------------------------------------------------------------------------------------4.0 to 15.0..................... 5 46 58 92 138

10 18 22 36 54

15 10 12 20 30

20 6 8 13 1915.1 to 25.0.................... 5 28 34 55 83

10 11 14 23 34

15 7 8 13 20

20 4 5 9 1325.1 to 36.0.................... 5 21 26 42 62

10 9 11 18 26

15 5 6 10 16

20 4 4 7 1136.1 to 46.0.................... 5 16 20 32 48

10 7 9 14 21

15 4 5 8 13

20 3 4 6 9----------------------------------------------------------------------------------------------------------------Notes:* This table is for open-air, phase-to-ground electric-arc exposures. It is not for phase-to-phase arcs or

enclosed arcs (arc in a box).[dagger] The table assumes that the employee will be 380 mm (15 in.) from the electric arc. The table also

assumes the arc length to be the sparkover distance for the maximum transient overvoltage of each voltage

range (see Appendix B to this subpart), as follows:

4.0 to 15.0 kV 51 mm (2 in.)15.1 to 25.0 kV 102 mm (4 in.)25.1 to 36.0 kV 152 mm (6 in.)36.1 to 46.0 kV 229 mm (9 in.)

[Dagger] The Occupational Safety and Health Administration calculated the values in this table using the ARCPRO

method listed in Table 2.** The voltage range is the phase-to-phase system voltage. Table 7--Incident Heat Energy for Various Fault Currents, Clearing Times, and Voltages: Live-Line Tool Exposures

Involving Phase-to-Ground Arcs in Open Air Only * [dagger] [Dagger] ----------------------------------------------------------------------------------------------------------------

Maximum clearing time (cycles)

Voltage range (kV) ** Fault current ---------------------------------------------------------------

10 73 92 147 220

15 39 49 78 117

20 24 31 49 7315.1 to 25.0.................... 5 197 246 394 591

10 75 94 150 225

15 41 51 82 122

20 26 33 52 7825.1 to 36.0.................... 5 138 172 275 413

10 53 66 106 159

15 30 37 59 89

20 19 24 38 5836.1 to 46.0.................... 5 129 161 257 386

10 51 64 102 154

15 29 36 58 87

20 19 24 38 5746.1 to 72.5.................... 20 18 23 36 55

30 10 13 20 30

40 6 8 13 19

50 4 6 9 1372.6 to 121.0................... 20 10 12 20 30

30 6 7 11 17

40 4 5 7 11

50 3 3 5 8121.1 to 145.0.................. 20 12 15 24 35

30 7 9 15 22

40 5 6 10 15

50 4 5 8 11145.1 to 169.0.................. 20 12 15 24 36

30 7 9 15 22

40 5 7 10 16

50 4 5 8 12169.1 to 242.0.................. 20 13 17 27 40

30 8 10 17 25

40 6 7 12 17

50 4 5 9 13242.1 to 362.0.................. 20 25 32 51 76

30 16 19 31 47

40 11 14 22 33

50 8 10 16 25362.1 to 420.0.................. 20 12 15 25 37

30 8 10 15 23

40 5 7 11 16

50 4 5 8 12420.1 to 550.0.................. 20 23 29 47 70

30 14 18 29 43

40 10 13 20 30

50 8 9 15 23550.1 to 800.0.................. 20 25 31 50 75

30 15 19 31 46

40 11 13 21 32

50 8 10 16 24----------------------------------------------------------------------------------------------------------------Notes:* This table is for open-air, phase-to-ground electric-arc exposures. It is not for phase-to-phase arcs or

enclosed arcs (arc in a box).[dagger] The table assumes the arc length to be the sparkover distance for the maximum phase-to-ground voltage

of each voltage range (see Appendix B to this subpart). The table also assumes that the employee will be the

minimum approach distance minus twice the arc length from the electric arc.[Dagger] The Occupational Safety and Health Administration calculated the values in this table using the ARCPRO

method listed in Table 2. For voltages of more than 72.6 kV, employers may use this table only when the minimum approach distance

established under Sec. 1926.960(c)(1) is greater than or equal to the following values:

72.6 to 121.0 kV 1.02 m121.1 to 145.0 kV 1.16 m145.1 to 169.0 kV 1.30 m169.1 to 242.0 kV 1.72 m242.1 to 362.0 kV 2.76 m362.1 to 420.0 kV 2.50 m420.1 to 550.0 kV 3.62 m550.1 to 800.0 kV 4.83 m** The voltage range is the phase-to-phase system voltage.

B. Selecting Protective Clothing and Other Protective Equipment

Paragraph (g)(5) of Sec. 1926.960 requires employers, in certain situations, to select protective clothing and other protective equipment with an arc rating that is greater than or equal to the incident heat energy estimated under Sec. 1926.960(g)(2). Based on laboratory testing required by ASTM F1506-10a, the expectation is that protective clothing with an arc rating equal to the estimated incident heat energy will be capable of preventing second-degree burn injury to an employee exposed to that incident heat energy from an electric arc. Note that actual electric-arc exposures may be more or less severe than the estimated value because of factors such as arc movement, arc length, arcing from reclosing of the system, secondary fires or explosions, and weather conditions. Additionally, for arc rating based on the fabric's arc thermal performance value \5\ (ATPV), a worker exposed to incident energy at the arc rating has a 50-percent chance of just barely receiving a second-degree burn. Therefore, it is possible (although not likely) that an employee will sustain a second-degree (or worse) burn wearing clothing conforming to Sec. 1926.960(g)(5) under certain circumstances. However, reasonable employer estimates and maintaining appropriate minimum approach distances for employees should limit burns to relatively small burns that just barely extend beyond the epidermis (that is, just barely a second-degree burn). Consequently, protective clothing and other protective equipment meeting Sec. 1926.960(g)(5) will provide an appropriate degree of protection for an employee exposed to electric-arc hazards.---------------------------------------------------------------------------

\5\ ASTM F1506-10a defines ``arc thermal performance value'' as ``the incident energy on a material or a multilayer system of materials that results in a 50% probability that sufficient heat transfer through the tested specimen is predicted to cause the onset of a second-degree skin burn injury based on the Stoll [footnote] curve, cal/cm\2\.'' The footnote to this definition reads: ``Derived from: Stoll, A.M., and Chianta, M.A., `Method and Rating System for Evaluations of Thermal Protection,' Aerospace Medicine, Vol 40, 1969, pp. 1232-1238 and Stoll A.M., and Chianta, M.A., `Heat Transfer through Fabrics as Related to Thermal Injury,' Transactions--New York Academy of Sciences, Vol 33(7), Nov. 1971, pp. 649-670.''---------------------------------------------------------------------------

Paragraph (g)(5) of Sec. 1926.960 does not require arc-rated protection for exposures of 2 cal/cm\2\ or less. Untreated cotton clothing will reduce a 2-cal/cm\2\ exposure below the 1.2- to 1.5-cal/cm\2\ level necessary to cause burn injury, and this material should not ignite at such low heat energy levels. Although Sec. 1926.960(g)(5) does not require clothing to have an arc rating when exposures are 2 cal/cm\2\ or less, Sec. 1926.960(g)(4) requires the outer layer of clothing to be flame resistant under certain conditions, even when the estimated incident heat energy is less than 2 cal/cm\2\, as discussed later in this appendix. Additionally, it is especially important to ensure that employees do not wear undergarments made from fabrics listed in the note to Sec. 1926.960(g)(3) even when the outer layer is flame resistant or arc rated. These fabrics can melt or ignite easily when an electric arc occurs. Logos and name tags made from non-flame-resistant material can adversely affect the arc rating or the flame-resistant characteristics of arc-rated or flame-resistant clothing. Such logos and name tags may violate Sec. 1926.960(g)(3), (g)(4), or (g)(5).

Paragraph (g)(5) of Sec. 1926.960 requires that arc-rated protection cover the employee's entire body, with limited exceptions for the employee's hands, feet, face, and head. Paragraph (g)(5)(i) of Sec. 1926.960 provides that arc-rated protection is not necessary for the employee's hands under the following conditions: For any estimated incident heat energy.... When the employee is wearing

rubber insulating gloves

with protectorsIf the estimated incident heat energy does When the employee is wearing

not exceed 14 cal/cm\2\. heavy-duty leather work

gloves with a weight of at

least 407 gm/m\2\ (12 oz/

yd\2\)

Paragraph (g)(5)(ii) of Sec. 1926.960 provides that arc-rated protection is not necessary for the employee's feet when the employee is wearing heavy-duty work shoes or boots. Finally, Sec. 1926.960(g)(5)(iii), (g)(5)(iv), and (g)(5)(v) require arc-rated head and face protection as follows: ----------------------------------------------------------------------------------------------------------------

Minimum head and face protection

------------------------------------------------------------------------------

Arc-rated faceshield

Exposure with a minimum Arc-rated hood or faceshield with

None * rating of 8 cal/ balaclava

cm\2\ *----------------------------------------------------------------------------------------------------------------Single-phase, open air........... 2-8 cal/cm\2\....... 9-12 cal/cm\2\...... 13 cal/\2\ or higher.[dagger]Three-phase...................... 2-4 cal/cm\2\....... 5-8 cal/cm\2\....... 9 cal/cm\2\ or higher.[Dagger]----------------------------------------------------------------------------------------------------------------* These ranges assume that employees are wearing hardhats meeting the specifications in Sec. 1910.135 or Sec.

1926.100(b)(2), as applicable.[dagger] The arc rating must be a minimum of 4 cal/cm\2\ less than the estimated incident energy. Note that Sec.

1926.960(g)(5)(v) permits this type of head and face protection, with a minimum arc rating of 4 cal/cm\2\

less than the estimated incident energy, at any incident energy level.[Dagger] Note that Sec. 1926.960(g)(5) permits this type of head and face protection at any incident energy

level.

IV. Protection Against Ignition

Paragraph (g)(3) of Sec. 1926.960 prohibits clothing that could melt onto an employee's skin or that could ignite and continue to burn when exposed to flames or to the available heat energy estimated by the employer under Sec. 1926.960(g)(2). Meltable fabrics, such as acetate, nylon, polyester, and polypropylene, even in blends, must be avoided. When these fibers melt, they can adhere to the skin, thereby transferring heat rapidly, exacerbating burns, and complicating treatment. These outcomes can result even if the meltable fabric is not directly next to the skin. The remainder of this section focuses on the prevention of ignition.

Paragraph (g)(5) of Sec. 1926.960 generally requires protective clothing and other protective equipment with an arc rating greater than or equal to the employer's estimate of available heat energy. As explained earlier in this appendix, untreated cotton is usually acceptable for exposures of 2 cal/cm\2\ or less.\6\ If the exposure is greater than that, the employee generally must wear flame-resistant clothing with a suitable arc rating in accordance with Sec. 1926.960(g)(4) and (g)(5). However, even if an employee is wearing a layer of flame-resistant clothing, there are circumstances under which flammable layers of clothing would be uncovered, and an electric arc could ignite them. For example, clothing ignition is possible if the employee is wearing flammable clothing under the flame-resistant clothing and the underlayer is uncovered because of an opening in the flame-resistant clothing. Thus, for purposes of Sec. 1926.960(g)(3), it is important for the employer to consider the possibility of clothing ignition even when an employee is wearing flame-resistant clothing with a suitable arc rating.---------------------------------------------------------------------------

\6\ See Sec. 1926.960(g)(4)(i), (g)(4)(ii), and (g)(4)(iii) for conditions under which employees must wear flame-resistant clothing as the outer layer of clothing even when the incident heat energy does not exceed 2 cal/cm\2\.---------------------------------------------------------------------------

Under Sec. 1926.960(g)(3), employees may not wear flammable clothing in conjunction with flame-resistant clothing if the flammable clothing poses an ignition hazard.\7\ Although outer flame-resistant layers may not have openings that expose flammable inner layers, when an outer flame-resistant layer would be unable to resist breakopen,\8\ the next (inner) layer must be flame-resistant if it could ignite.---------------------------------------------------------------------------

\7\ Paragraph (g)(3) of Sec. 1926.960 prohibits clothing that could ignite and continue to burn when exposed to the heat energy estimated under paragraph (g)(2) of that section.

\8\ Breakopen occurs when a hole, tear, or crack develops in the exposed fabric such that the fabric no longer effectively blocks incident heat energy.---------------------------------------------------------------------------

Non-flame-resistant clothing can ignite even when the heat energy from an electric arc is insufficient to ignite the clothing. For example, nearby flames can ignite an employee's clothing; and, even in the absence of flames, electric arcs pose ignition hazards beyond the hazard of ignition from incident energy under certain conditions. In addition to requiring flame-resistant clothing when the estimated incident energy exceeds 2.0 cal/cm\2\, Sec. 1926.960(g)(4) requires flame-resistant clothing when: The employee is exposed to contact with energized circuit parts operating at more than 600 volts (Sec. 1926.960(g)(4)(i)), an electric arc could ignite flammable material in the work area that, in turn, could ignite the employee's clothing (Sec. 1926.960(g)(4)(ii)), and molten metal or electric arcs from faulted conductors in the work area could ignite the employee's clothing (Sec. 1926.960(g)(4)(iii)). For example, grounding conductors can become a source of heat energy if they cannot carry fault current without failure. The employer must consider these possible sources of electric arcs \9\ in determining whether the employee's clothing could ignite under Sec. 1926.960(g)(4)(iii).---------------------------------------------------------------------------

\9\ Static wires and pole grounds are examples of grounding conductors that might not be capable of carrying fault current without failure. Grounds that can carry the maximum available fault current are not a concern, and employers need not consider such grounds a possible electric arc source. ---------------------------------------------------------------------------

Sec. Appendix F to Subpart V of Part 1926--Work-Positioning Equipment

Inspection Guidelines

I. Body Belts

Inspect body belts to ensure that:

A. The hardware has no cracks, nicks, distortion, or corrosion;

B. No loose or worn rivets are present;

C. The waist strap has no loose grommets;

D. The fastening straps are not 100-percent leather; and

E. No worn materials that could affect the safety of the user are present.

II. Positioning Straps

Inspect positioning straps to ensure that:

A. The warning center of the strap material is not exposed;

B. No cuts, burns, extra holes, or fraying of strap material is present;

C. Rivets are properly secured;

D. Straps are not 100-percent leather; and

E. Snaphooks do not have cracks, burns, or corrosion.

III. Climbers

Inspect pole and tree climbers to ensure that:

A. Gaffs are at least as long as the manufacturer's recommended minimums (generally 32 and 51 millimeters (1.25 and 2.0 inches) for pole and tree climbers, respectively, measured on the underside of the gaff);

Note: Gauges are available to assist in determining whether gaffs are long enough and shaped to easily penetrate poles or trees.

B. Gaffs and leg irons are not fractured or cracked;

C. Stirrups and leg irons are free of excessive wear;

D. Gaffs are not loose;

E. Gaffs are free of deformation that could adversely affect use;

F. Gaffs are properly sharpened; and

G. There are no broken straps or buckles.

Sec. Appendix G to Subpart V of Part 1926--Reference Documents

The references contained in this appendix provide information that can be helpful in understanding and complying with the requirements contained in Subpart V of this part. The national consensus standards referenced in this appendix contain detailed specifications that employers may follow in complying with the more performance-based requirements of Subpart V of this part. Except as specifically noted in Subpart V of this part, however, the Occupational Safety and Health Administration will not necessarily deem compliance with the national consensus standards to be compliance with the provisions of Subpart V of this part.ANSI/SIA A92.2-2009, American National Standard for Vehicle-Mounted

Elevating and Rotating Aerial Devices.ANSI Z133-2012, American National Standard Safety Requirements for

Arboricultural Operations--Pruning, Trimming, Repairing,

Maintaining, and Removing Trees, and Cutting Brush.ANSI/IEEE Std 935-1989, IEEE Guide on Terminology for Tools and

Equipment to Be Used in Live Line Working.ASME B20.1-2012, Safety Standard for Conveyors and Related Equipment.ASTM D120-09, Standard Specification for Rubber Insulating Gloves.ASTM D149-09 (2013), Standard Test Method for Dielectric Breakdown

Voltage and Dielectric Strength of Solid Electrical Insulating

Materials at Commercial Power Frequencies.ASTM D178-01 (2010), Standard Specification for Rubber Insulating

Matting.ASTM D1048-12, Standard Specification for Rubber Insulating Blankets.ASTM D1049-98 (2010), Standard Specification for Rubber Insulating

Covers.ASTM D1050-05 (2011), Standard Specification for Rubber Insulating Line

Hose.ASTM D1051-08, Standard Specification for Rubber Insulating Sleeves.ASTM F478-09, Standard Specification for In-Service Care of Insulating

Line Hose and Covers.ASTM F479-06 (2011), Standard Specification for In-Service Care of

Insulating Blankets.ASTM F496-08, Standard Specification for In-Service Care of Insulating

Gloves and Sleeves.ASTM F711-02 (2007), Standard Specification for Fiberglass-Reinforced

Plastic (FRP) Rod and Tube Used in Live Line Tools.ASTM F712-06 (2011), Standard Test Methods and Specifications for

Electrically Insulating Plastic Guard Equipment for Protection

of Workers.ASTM F819-10, Standard Terminology Relating to Electrical Protective

Equipment for Workers.ASTM F855-09, Standard Specifications for Temporary Protective Grounds

to Be Used on De-energized Electric Power Lines and Equipment.ASTM F887-12\e1\, Standard Specifications for Personal Climbing

Equipment.ASTM F914/F914M-10, Standard Test Method for Acoustic Emission for

Aerial Personnel Devices Without Supplemental Load Handling

Attachments.ASTM F1116-03 (2008), Standard Test Method for Determining Dielectric

Strength of Dielectric Footwear.ASTM F1117-03 (2008), Standard Specification for Dielectric Footwear. ASTM F1236-96 (2012), Standard Guide for Visual Inspection of Electrical

Protective Rubber Products.ASTM F1430/F1430M-10, Standard Test Method for Acoustic Emission Testing

of Insulated and Non-Insulated Aerial Personnel Devices with

Supplemental Load Handling Attachments.ASTM F1505-10, Standard Specification for Insulated and Insulating Hand

Tools.ASTM F1506-10a, Standard Performance Specification for Flame Resistant

and Arc Rated Textile Materials for Wearing Apparel for Use by

Electrical Workers Exposed to Momentary Electric Arc and

Related Thermal Hazards.ASTM F1564-13, Standard Specification for Structure-Mounted Insulating

Work Platforms for Electrical Workers.ASTM F1701-12, Standard Specification for Unused Polypropylene Rope with

Special Electrical Properties.ASTM F1742-03 (2011), Standard Specification for PVC Insulating

Sheeting.ASTM F1796-09, Standard Specification for High Voltage Detectors--Part 1

Capacitive Type to be Used for Voltages Exceeding 600 Volts

AC.ASTM F1797-09 [egr] \1\, Standard Test Method for Acoustic Emission

Testing of Insulated and Non-Insulated Digger Derricks.ASTM F1825-03 (2007), Standard Specification for Clampstick Type Live

Line Tools.ASTM F1826-00 (2011), Standard Specification for Live Line and Measuring

Telescoping Tools.ASTM F1891-12, Standard Specification for Arc and Flame Resistant

Rainwear.ASTM F1958/F1958M-12, Standard Test Method for Determining the

Ignitability of Non-flame-Resistant Materials for Clothing by

Electric Arc Exposure Method Using Mannequins.ASTM F1959/F1959M-12, Standard Test Method for Determining the Arc

Rating of Materials for Clothing.IEEE Stds 4-1995, 4a-2001 (Amendment to IEEE Standard Techniques for

High-Voltage Testing), IEEE Standard Techniques for High-

Voltage Testing.IEEE Std 62-1995, IEEE Guide for Diagnostic Field Testing of Electric

Power Apparatus--Part 1: Oil Filled Power Transformers,

Regulators, and Reactors.IEEE Std 80-2000, Guide for Safety in AC Substation Grounding.IEEE Std 100-2000, The Authoritative Dictionary of IEEE Standards Terms

Seventh Edition.IEEE Std 516-2009, IEEE Guide for Maintenance Methods on Energized Power

Lines.IEEE Std 524-2003, IEEE Guide to the Installation of Overhead

Transmission Line Conductors.IEEE Std 957-2005, IEEE Guide for Cleaning Insulators.IEEE Std 1048-2003, IEEE Guide for Protective Grounding of Power Lines.IEEE Std 1067-2005, IEEE Guide for In-Service Use, Care, Maintenance,

and Testing of Conductive Clothing for Use on Voltages up to

765 kV AC and 750 kV DC.IEEE Std 1307-2004, IEEE Standard for Fall Protection for Utility Work.IEEE Stds 1584-2002, 1584a-2004 (Amendment 1 to IEEE Std 1584-2002), and

1584b-2011 (Amendment 2: Changes to Clause 4 of IEEE Std 1584-

2002), IEEE Guide for Performing Arc-Flash Hazard

Calculations.IEEE C2-2012, National Electrical Safety Code.NFPA 70E-2012, Standard for Electrical Safety in the Workplace.