Laws and Regulations
Pacific Gas and Electric Company, is a California-based utility, regulated by the California Public Utilities Commission (CPUC). Pacific Gas and Electric Company will obtain a reasonable amount of clearance beyond the minimum requirements to allow for a several years worth of growth, potential wind sway and other environmental factors. Distance obtained from the line after a pruning cycle may be more than 20 feet for fast growing species such as a mulberry or eucalyptus trees along distribution lines and for high voltage transmission lines 4 years or 40 feet of clearance is required.
There are rules and regulations designed to ensure public safety and electric service reliability. Major regulations covering vegetation management include:
- Public Resource Code 4292: Firebreak Clearing
Utilities are required to maintain firebreaks around poles located in wild land areas during fire season that have certain equipment with the potential to emit sparks when operating properly.
- Public Resource Code 4293: State Responsibility
Utilities are required to maintain clearance between vegetation and high voltage power lines during fire season in wild land areas to prevent wild fires. Also requires removal of dead, diseased or dying trees that could fall into power lines.
- General Order 95: Utility Vegetation Management Requirements
Utilities are required to maintain clearance between vegetation and high voltage power lines at all times in all areas for public safety and electric system reliability.
- North American Electric Reliability Council (NERC) Standard FAC-003-1: Transmission Vegetation Management Standard
FAC-003-1 is a Federal Energy Regulatory Commission (FERC) mandated standard, enforced by NERC which requires utilities to take preventative action to reduce widespread outages caused by vegetation conflicts on critical electric transmission lines over 60,000 volts. Utilities must have a formal vegetation management program that meets specific standards and maintains required clearances between vegetation and transmission electric facilities at all times in all conditions.
Public Resource Code, Section 4292: Power Line Hazard Reduction
Except as otherwise provided in Section 4296, any person that owns, controls, operates, or maintains any electrical transmission or distribution line upon any mountainous land, or forest-covered land, brush-covered land, or grass-covered land shall, during such times and in such areas as are determined to be necessary by the director or the agency which has primary responsibility for fire protection of such areas, 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. This section does not, however, apply to any line which is used exclusively as telephone, telegraph, telephone or telegraph messenger call, fire or alarm line, or other line which is classed as a communication circuit by the Public Utilities Commission. The director or the agency which has primary fire protection responsibility for the protection of such areas may permit exceptions from the requirements of this section which are based upon the specific circumstances involved.
Section 1254 - Minimum Clearance Provisions
The firebreak clearances required by PRC 4292 are applicable within an imaginary cylindrical space surrounding each pole or tower on which a switch, fuse, transformer or lightning arrester is attached and surrounding each dead-end or corner pole, unless such pole or tower is exempt from minimum clearance requirements by provisions of 14, CCR, 1255 or PRC 4296. The radius of the cylindroid is 3.1 m (10 feet) measured horizontally from the outer circumference of the specified pole or tower with height equal to the distance from the intersection of the imaginary vertical exterior surface of the cylindroid with the ground to an intersection with a horizontal plane passing through the highest point at which a conductor is attached to such pole or tower. Flammable vegetation and materials located wholly or partially within the firebreak space shall be treated as follows:
- (a) At ground level - remove flammable materials, including but not limited to, ground litter, duff and dead or desiccated vegetation that will propagate fire, and;
- (b) From 0 - 2.4 m (0-8 feet) above ground level remove flammable trash, debris or other materials, grass, herbaceous and brush vegetation. All limbs and foliage of living trees shall be removed up to a height of 2.4 m (8 feet).
- (c) From 2.4 m (8 feet) to horizontal plane of highest point of conductor attachment remove dead, diseased or dying limbs and foliage from living sound trees and any dead, diseased or dying trees in their entirety.
Figure 1: Graphical representation of Section 1254 showing the minimum clearances required around a utility pole.
Public Resource Code, Section 4293: Line Clearance Guidelines
Except as otherwise provided in Sections 4294 to 4296, inclusive, any person that owns, controls, operates, or maintains any electrical transmission or distribution line upon any mountainous land, or in forest-covered land, brush-covered land, or grass-covered land shall, during such times and in such areas as are determined to be necessary by the director or the agency which has primary responsibility for the fire protection of such areas, maintain a clearance of the respective distances which are specified in this section in all directions between all vegetation and all conductors which are carrying electric current:
- (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 pruned so as to remove such hazard. The director or the agency which has primary responsibility for the fire protection of such areas may permit exceptions from the requirements of this section which are based upon the specific circumstances involved.
General Order 95, Rule 35: Tree Pruning
Where overhead conductors traverse trees and vegetation, safety and reliability of service demand that certain vegetation management activities be performed in order to establish necessary and reasonable clearances the minimum clearances set forth in Table 1, Cases 13 and 14, measured between line conductors and vegetation under normal conditions, shall be maintained. (Also see Appendix E for tree trimming guidelines.) These requirements apply to all overhead electrical supply and communication facilities that are covered by this General Order, including facilities on lands owned and maintained by California state and local agencies.
When a supply or communication company has actual knowledge, obtained either through normal operating practices or notification to the company, that dead, rotten or diseased trees or dead, rotten or diseased portions of otherwise healthy trees overhang or lean toward and may fall into a span of supply or communication lines, said trees or portions thereof should be removed.
Communication and electric supply circuits, energized at 750 volts or less, including their service drops, should be kept clear of vegetation in new construction and when circuits are reconstructed or repaired, whenever practicable. When a supply or communication company has actual knowledge, obtained either through normal operating practices or notification to the company, that its circuit energized at 750 volts or less shows strain or evidences abrasion from vegetation contact, the condition shall be corrected by reducing conductor tension, rearranging or replacing the conductor, pruning the vegetation, or placing mechanical protection on the conductor(s). For the purpose of this rule, abrasion is defined as damage to the insulation resulting from the friction between the vegetation and conductor. Scuffing or polishing of the insulation or covering is not considered abrasion. Strain on a conductor is present when vegetation contact significantly compromises the structural integrity of supply or communication facilities. Contact between vegetation and conductors, in and of itself, does not constitute a nonconformance with the rule.
Note: Revised January 13, 2006 by Decision No. 05-01-030, August 20, 2009 by Decision No. 09-08-029 and January 12, 2012 by Decision No. 12-01-032
- (1) Rule 35 requirements do not apply to conductors, or aerial cable that complies with Rule 57.4-C, energized at less than 60,000 volts, where trimming or removal is not practicable and the conductor is separated from the tree with suitable materials or devices to avoid conductor damage by abrasion and grounding of the circuit through the tree.
- (2) Rule 35 requirements do not apply where the supply or communication company has made a "good faith" effort to obtain permission to trim or remove vegetation but permission was refused or unobtainable. A "good faith" effort shall consist of current documentation of a minimum of an attempted personal contact and a written communication, including documentation of mailing or delivery. The written communication may include a statement that the company may seek to recover any costs and liabilities incurred by the company due to its inability to trim or remove vegetation. However, this does not preclude other action or actions from demonstrating "good faith". If permission to trim or remove vegetation is unobtainable and requirements of exception 2 are met, the company is not compelled to comply with the requirements of exception 1.
- (3) The Commission recognizes that unusual circumstances beyond the control of the utility may result in nonconformance with the rules. In such cases, the utility may be directed by the Commission to take prompt remedial action to come into conformance, whether or not the nonconformance gives rise to penalties or is alleged to fall within permitted exceptions or phase–in requirements.
Note: Revised November 6,1992 by Resolution No. SU–15, September 20, 1996 by Decision No. 96–09–097 and January 23, 1997 by Decision No. 97–01–044.
- (4) Mature trees whose trunks and major limbs are located more than six inches, but less than the clearance required by Table 1, Cases 13E and 14E, from primary distribution conductors are exempt from the minimum clearance requirement under this rule. The trunks and limbs to which this exemption applies shall only be those of sufficient strength and rigidity to prevent the trunk or limb from encroaching upon the six-inch minimum clearance under reasonably foreseeable local wind and weather conditions. The utility shall bear the risk of determining whether this exemption applies, and the Commission shall have final authority to determine whether the exemption applies in any specific instance, and to order that corrective action be taken in accordance with this rule, if it determines that the exemption does not apply.
Note: Added October 22, 1997 by Decision No. 97–10–056
The following are guidelines to Rule 35.
The radial clearances shown below are minimum clearances that should be established, at time of pruning, between the vegetation and the energized conductors and associated live parts where practicable.
Vegetation management practices may make it advantageous to obtain greater clearances than those listed below:
A. Radial clearances for any conductor of a line operating at 2,400 or more volts, but less than 72,000 volts 4 feet
B. Radial clearances for any conductor of a line operating at 72,000 or more volts, but less than 110,000 volts 6 feet
C. Radial clearances for any conductor of a line operating at 110,000 or more volts, but less than 300,000 volts 10 feet
D. Radial clearances for any conductor of a line operating at 300,000 or more 15 feet
|Case No.||Nature of Clearance||Wire or Conductor Concerned|
|Span Wires (Other than Trolley Span Wires) Overhead Guys and Messengers||Communication Conductors (Including Open Wire, Cables and Service Drops), Supply Service Drops of 0 - 750 Volts||Tolley Contact, Feeder and Span wires, 0 - 5,000 Volts|
|13||Radial clearance of bare line conductors from tree branches or foliage (aaa)(ddd)||--||--||18 inches (bbb)|
|Case No.||Nature of Clearance||Wire or Conductor Concerned|
|Supply Conductors of 0 - 750 Volts and Supply Cables Treated as in Rule 57.8||Supply Conductors and Supply Cables, 750 - 22,500 Volts||Supply Conductors and Supply Cables, 22.5 - 300 kV||Supply Conductors and Supply Cables, 300 - 550 kV(mm)|
|13||Radial clearance of bare line conductors from tree branches or foliage (aaa) (ddd)||--||18 inches (bbb)||1/4 pin spacing shown in table 2, Case 15 (bbb) (ccc)||1/2 pin spacing shown in table 2, Case 15|
(aaa) Special requirements for communication and supply circuits energized at 0 - 750 volt
(bbb) May be Reduced for conductor of less than 60,000 volts when protected from abrasion and grounding by contact with tree.
(ccc) For 22.5 kV to 105 kV, minimum clearance shall be 18 inches.
(ddd) Clearances in this case shall be maintained for normal annual weather variations, rather than at 60 degrees, no wind.