Investor-owned electric utilities in California are required by the Public Resources Code, and through the Public Utilities Code and specifically General Order (G.O.) 95 of the California Public Utilities Commission (Commission), to maintain a distance between electric power lines and all vegetation. However, although both requirements direct electric utilities to maintain tree-line clearance, they differ in the specific distance required.

In "any mountainous land, or in forest-covered land, brush-covered land, or grass-covered land" within "state responsibility areas," Public Resources Code section 4293 requires a clearance of four feet, six feet or ten feet between vegetation and all conductors depending on the voltage at which the power line operates.1 It specifies:

(a) For any line which is operating at 2,400 or more volts, but less than 72,000 volts, four feet.
(b) For any line which is operating at 72,000 or more volts, but less than 110,000 volts, six feet.
(c) For any line which is operating at 110,000 or more volts, 10 feet.
In every case, such distance shall be sufficiently great to furnish the required clearance at any position of the wire, or conductor when the adjacent air temperature is 120 degrees Fahrenheit, or less. Dead trees, old decadent or rotten trees, trees weakened by decay or disease and trees or portions thereof that are leaning toward the line which may contact the line from the side or may fall on the line shall be felled, cut, or trimmed so as to remove such hazard.2

Public Resources Code section 4292 also orders utilities to maintain "around and adjacent to any pole or tower which supports a switch, fuse, transformer, lightning arrester, line junction, or dead end or corner pole, a firebreak which consists of a clearing of not less than 10 feet in each direction from the outer circumference of such pole or tower" in "any mountainous land, or in forest-covered land, brush-covered land, or grass-covered land" within "state responsibility areas."3

In contrast to such specific requirements, the Commission's clearance rule formerly only required utilities to maintain "a reasonable amount of tree trimming . . . in order that the wires may clear branches and foliage."4 The Commission approved changes to that standard in 1997. According to the amended Rule 35 of G.O. 95 and Table 1 referred therein, a minimum clearance of 18 inches must be maintained "between line conductors and vegetation under normal conditions."5 The Commission's 18 inch standard is clearly more lenient than the clearance requirements of the Public Resources Code. Utilities would need to trim more trees to obey the Public Resources Code. Thus, the question arises whether more severe clearance requirements can be imposed upon utilities when the Commission requires clearance of only 18 inches.