Overhead power line clearance by voltage in California
Updated: Sep 21
California's enforceable minimum is GO 95 Table 1, Cases 13 and 14. Case 13 requires 18 inches for supply conductors of 750 to 22,500 volts, and Case 14 requires 48 inches for the same conductors inside the High Fire-Threat District. Above 22,500 volts both cases change with voltage. Below 750 volts the table gives no number at all.
Ask what clearance an overhead line needs from vegetation in California and the answer that comes back is usually 18 inches, or 4 feet, or 12 feet, depending on who is asked. All three are real numbers from the same rule, and none of them is the answer on its own. The enforceable minimum lives in one place, General Order 95, Table 1, Cases 13 and 14, and reading it by voltage means reading it by column first. Two of those columns answer with a formula rather than a distance.
Which column the conductor sits in
Table 1 is organized by facility class before it is organized by voltage. It has seven columns:
Column | What it covers |
A | Span wires other than trolley span wires, overhead guys and messengers |
B | Communication conductors, including open wire, cables and service drops, and supply service drops of 0 to 750 volts |
C | Trolley contact, feeder and span wires, 0 to 5,000 volts |
D | Supply conductors of 0 to 750 volts, and supply cables treated as in Rule 57.8 |
E | Supply conductors and supply cables, 750 to 22,500 volts |
F | Supply conductors and supply cables, 22.5 to 300 kV |
G | Supply conductors and supply cables, 300 to 550 kV |
Cases 13 and 14 run across those seven columns, and in both rows three cells are empty. Columns A, B and D carry a dash. Only C, E, F and G carry a value.
That is the first thing a by-voltage reading has to account for, because it is a facility question wearing a voltage costume. On a distribution pole carrying a 12 kV primary above a 120/240 volt service drop, the primary has a tabulated radial clearance and the drop below it does not. The drop is column B, the secondary is column D, and neither has a number in Case 13 or Case 14.
What voltage means in Table 1
Rule 24.1 settles it in one sentence: voltage "means the highest effective voltage between any two conductors of the circuit concerned except where, in certain rules, the term 'voltage (or volts) to ground' is used." Cases 13 and 14 do not use the "to ground" form, so a three-phase distribution circuit is read phase to phase. A 12 kV circuit and a 21 kV circuit are both column E. A 33 kV circuit is column F.
Rule 24.1 then adds a case that catches people out:
When one circuit is directly connected to another circuit of higher voltage (as in the case of an autotransformer) both are considered as of the higher voltage unless the circuit of the lower voltage is effectively grounded.
The lower circuit takes the higher circuit's column, and with it the higher circuit's clearance. For direct current, Table 1 footnote (nn) displaces Rule 24.1 entirely: "Voltage shown in the table shall mean line to ground voltage for direct current (DC) systems."
The column ranges are printed so that they touch. Column E ends at 22,500 volts and column F begins at 22.5 kV; column F ends at 300 kV and column G begins at 300 kV. A conductor at exactly those figures appears in two columns and the table prints no tie-break. At 22,500 volts nothing turns on it, since both columns produce 18 inches under Case 13 and 48 inches under Case 14. At 300 kV the choice is between 37.5 inches and 75.
Case 13, outside the fire-threat district
Case 13 is titled "Radial clearance of bare line conductors from tree branches or foliage." Four cells carry values:
Column | Voltage class | Case 13 |
C | Trolley contact, feeder and span wires, 0 to 5,000 V | 18 inches |
E | Supply conductors and cables, 750 to 22,500 V | 18 inches |
F | Supply conductors and cables, 22.5 to 300 kV | one quarter of the pin spacing in Table 2, Case 15, and not less than 18 inches from 22.5 kV to 105 kV |
G | Supply conductors and cables, 300 to 550 kV | one half of the pin spacing in Table 2, Case 15 |
The 18 inches in column E is the figure everyone quotes, and for distribution it is correct. Above 22,500 volts the table stops giving distances. Column F reads "1/4 pin spacing shown in Table 2, Case 15," and Table 2, Case 15 is the horizontal separation of conductors on the same crossarm, listed by voltage class:
Voltage class | Pin spacing |
20,000 to 35,000 volts | 24 inches |
35,000 to 75,000 volts | 48 inches |
75,000 to 150,000 volts | 60 inches, with 0.40 inch added for every kV above 75 |
150,000 to 300,000 volts | 90 inches, with 0.40 inch added for every kV above 150 |
Worked through, a 66 kV subtransmission line has a pin spacing of 48 inches, one quarter of which is 12 inches. Footnote (ccc) then puts a floor under it: "For 22.5 kV to 105 kV, minimum clearance shall be 18 inches." The answer is 18 inches, the same number as the 12 kV feeder underbuilt on the same poles.
The floor stops exactly where the formula catches up with it. At 105 kV the pin spacing is 60 plus 0.40 times 30, which is 72 inches, and one quarter of 72 is 18. Above 105 kV the formula runs alone: 19 inches at 115 kV, 30.5 inches at 230 kV, 37.5 inches at 300 kV.
Column G doubles the fraction to one half, so a 500 kV line, whose Table 2 pin spacing is 150 inches plus 0.40 inch for every kV above 300, or 230 inches, carries 115 inches. Above 550 kV Table 1 gives out: footnote (mm) requires proposed clearances to be filed with the Commission before construction.
Case 14, inside the district
Case 14 is titled "Radial clearance of bare line conductors from vegetation in Extreme and Very High Fire Threat Zones in Southern California." Footnote (hhh) has since overtaken that caption, defining the case against the High Fire-Threat District in GO 95 Rule 21.2-D. Footnote (jjj) then lifts plowed or cultivated orchards of fruit, nut or citrus trees back out and returns them to Case 13.
Voltage | Case 14 |
Less than 2,400 volts (column E) | 48 inches, which footnote (iii) permits to be reduced to 18 inches |
2,400 to 22,500 volts (column E) | 48 inches |
22.5 kV to 72 kV (column F) | 48 inches |
72 kV to 110 kV (column F) | 72 inches, by footnote (fff) |
Above 110 kV to 300 kV (column F) | 120 inches, by footnote (fff) |
300 to 550 kV (column G) | 120 inches, plus 0.40 inch per kV above 500 kV, by footnote (ggg) |
Column C does not move. A trolley contact wire carries 18 inches inside the district exactly as it does outside.
Two steps in that table are worth marking before a cycle is planned. The first is at 2,400 volts. Footnote (iii) reads "May be reduced to 18 inches for conductors operating less than 2.4 kV," and the operative word is may. It is a permission, not a lower requirement.
A span held to 18 inches has to be identifiable in the record as a span the reduction was taken on. The second step is at 110 kV, where footnote (fff) moves the clearance from 72 inches to 120. A 115 kV line in Tier 2 carries a 10 foot minimum and the 110 kV line on the next alignment carries 6 feet. Five kV of operating voltage, four feet of clearance.
Where the two cases nearly meet
At distribution voltage, being inside the High Fire-Threat District is expensive: 48 inches against 18, a ratio of nearly three to one. At the top of the transmission range it costs almost nothing. A 500 kV line outside the district needs 115 inches under Case 13. Inside the district it needs 120 under Case 14. Five inches separate them.
The convergence is arithmetic rather than policy. Case 13 above 300 kV is a fraction of a pin spacing that is itself indexed to voltage, so it climbs on its own, while Case 14 sits flat at 120 inches until 500 kV. In the middle of the range the two have not converged at all: at 230 kV, Case 13 asks 30.5 inches and Case 14 asks 120.
Both cases say bare line conductors
Cases 13 and 14 are each titled for the radial clearance of bare line conductors, and that word does work. Covered conductor is not bare. It is not suitably insulated either, because Rule 20.9-G states that "a weather-resistant covering of a supply conductor does not meet the requirements of this rule as to suitable insulation."
The only place Rule 35 gives a covering any weight is Exception 1. It reaches conductors and Rule 57.4-C aerial cable energized at less than 60,000 volts, and only where trimming or removal is not practicable and the conductor is separated from the tree by suitable materials or devices.
That exception turns on impracticability, not on the covering, and it is conditioned in ways that cost something to satisfy. Whether a covered 12 kV conductor in Tier 3 sits inside Case 14 is not a question Table 1 answers. Until it is answered, the defensible position is a record that states which clearance was applied to that span and on what basis.
Below 750 volts there is no number
The blank cells in columns B and D are not an omission. Footnote (aaa) is attached to both Case 13 and Case 14 and reads "Special requirements for communication and supply circuits energized at 0 - 750 volts - Rule 35." It sends the reader out of the table and into the rule's third paragraph, which sets a condition instead of a distance.
A secondary or a service drop has to be kept clear where practicable when it is built, reconstructed or repaired, and has to be corrected once the company knows vegetation is straining or abrading it. What strain and abrasion mean there, and why contact alone is not a nonconformance, the rule defines for itself.
Column C is the one place voltage stops mattering in the usual way. A trolley contact wire at 600 volts carries 18 inches in both cases, while a 600 volt supply conductor on the pole beside it carries nothing tabulated at all. The difference is the facility class, not the volts.
So the honest answer to "how far does a service drop have to be from that limb" is that Table 1 does not set a distance. What was measured, and from what surface, still belongs in the record. There is simply no tabular value to compare it against.
The recommended numbers use different bands
Rule 35 also points to Appendix E, whose guidelines are what most crews actually cut to, and Appendix E does not use Table 1's voltage bands. It breaks at 2,400 volts, 72,000 volts, 110,000 volts and 300,000 volts. Table 1 breaks at 750 volts, 22,500 volts, 300 kV and 550 kV. Only the 300 kV boundary is shared, and Appendix E says nothing at all below 2,400 volts.
The gap that opens is widest through the transmission range. A 115 kV line inside the High Fire-Threat District falls in Appendix E's 110,000 to 300,000 volt band, where the recommendation is 30 feet at time of trim. The same line is column F above 110 kV in Table 1, where the enforceable minimum is 120 inches. Thirty feet is the target and ten feet is the line. Outside the district the ratio is wider still: 10 feet recommended against 19 inches enforced.
Appendix E is explicit about its own status. Its distances are "recommended minimum clearances that should be established, at time of trimming, between the vegetation and the energized conductors and associated live parts where practicable." Should, and where practicable. Which of the two numbers a crew works to and which one an inspector measures against is worth settling before a cycle starts.
What the record has to name
A measured distance is not a finding until it carries the case and the column that produced the number it was measured against. "Span cleared to 51 inches" is not auditable by anyone. "12 kV, Case 14, column E, 51 inches at the closest approach on the west phase, measured August 14, 2026" is, because every element can be checked back to the table by someone who was not there.
The date is not decoration. These two cases are the only rows in Table 1 that footnote (ddd) reaches, which takes them off the still-air benchmark the rest of the table is measured on and puts them on a condition that has to hold through the year. A distance recorded without the conditions it was taken under cannot be tested against that standard at all.
What a working clearance record contains and how the growth between cycles is accounted for are their own subjects; the table's own contribution is that it makes the case and column checkable, and an evaluator will look for both.
Table 1 was last revised on December 21, 2017 by Decision 17-12-024, the same decision that adopted the statewide fire-threat map. The numbers above are that version.
Where the table stops
Table 1 is the Commission's number and it is rarely the only one on a span. On mountainous, forest-covered, brush-covered or grass-covered land, PRC 4293 sets its own distances on its own voltage bands. It requires them at any position of the conductor "when the adjacent air temperature is 120 degrees Fahrenheit, or less." That is a different measurement condition from footnote (ddd). Where the two rules' numbers diverge and what PRC 4293 requires radially are separate pages, as is which agency enforces which of them.
At 200 kV and above, a third number arrives from a different direction. NERC FAC-003 works from a Minimum Vegetation Clearance Distance derived from a flashover calculation at the conductor's own operating conditions, not from a table of voltage classes, and which lines it reaches is a question about the transmission system rather than about voltage alone. On a 230 kV line crossing brush-covered land inside the High Fire-Threat District, all three regimes can be live at once, and they do not produce the same figure.
Further reading
CPUC GO 95 Rule 35: the vegetation clearance rule, explained: The rule these numbers sit inside, and the four exceptions that move them.
Time-of-trim clearance versus maintained clearance: Why a crew cuts to Appendix E and an inspector measures against Table 1.
GO 95 Rule 35 and PRC 4293: two rules, two different clearances: The second set of distances that lands on the same span in an SRA.
Frequently asked questions
What is the minimum vegetation clearance for a 12 kV line in California?
Eighteen inches, under GO 95 Table 1, Case 13, column E, which covers supply conductors and supply cables of 750 to 22,500 volts. Inside the High Fire-Threat District, Case 14 raises the same column to 48 inches. Appendix E's larger figures are time-of-trim guidelines, not the enforceable minimum.
Does Table 1 give a clearance for a 115 kV line?
Not as a distance. Case 13 column F reads one quarter of the pin spacing shown in Table 2, Case 15. At 115 kV that pin spacing is 60 inches plus 0.40 inch for each kV above 75, or 76 inches, so the Case 13 clearance works out at 19 inches. Case 14 sets 120 inches at that voltage by footnote (fff).
Is there a required clearance between vegetation and a service drop?
No tabulated one. Cases 13 and 14 leave columns B and D blank, and footnote (aaa) sends circuits energized at 0 to 750 volts to Rule 35 itself. The rule sets a condition rather than a distance: the circuit must be corrected once the company has actual knowledge that it shows strain or evidences abrasion from vegetation contact.
Which voltage figure decides the column?
The highest effective voltage between any two conductors of the circuit concerned, under GO 95 Rule 24.1, so a three-phase distribution circuit is read phase to phase rather than to ground. Table 1 footnote (nn) overrides that for direct current systems, where the table's voltage means line-to-ground voltage.
