The requirements of Sec. 1926.1407 and Sec. 1926.1408 apply to power lines over 350 kV except:
(a) For power lines at or below 1000 kV, wherever the distance ``20 feet'' is specified, the distance ``50 feet'' must be substituted; and
(b) For power lines over 1000 kV, the minimum clearance distance must be established by the utility owner/operator or registered professional engineer who is a qualified person with respect to electrical power transmission and distribution.