Minimum clearances between uninsulated electrical conductor surfaces, or between uninsulated conductor surfaces and grounded metal surfaces, within the enclosure shall be as follows:
Minimum Clearances Between Uninsulated Surfaces------------------------------------------------------------------------
Clearances (inches)
-----------------------
Phase-to-
Phase-to-Phase Voltage (rms) Phase-to- Ground or
Phase Control
Circuit------------------------------------------------------------------------0 to 250........................................ 0.25 0.25251 to 600...................................... 0.28 0.25601 to 1000..................................... 0.61 0.251001 to 2400.................................... 1.4 0.62401 to 4160.................................... 3.0 1.4------------------------------------------------------------------------ [57 FR 61209, Dec. 23, 1992]