PRC 4293: radial clearance in State Responsibility Areas

On mountainous, forest, brush or grass covered land, PRC 4293 requires four feet between vegetation and conductors carrying current at 2,400 to 72,000 volts, six feet to 110,000, and ten feet above. 14 CCR 1256 measures it at a right angle to the conductor axis through a full 360 degree arc, at any position conductor or vegetation may move.

A 69 kV subtransmission circuit and the 12 kV feeder underbuilt on the same poles carry the same clearance obligation under the Public Resources Code: four feet, from every conductor carrying current, in every direction. The 115 kV line on the next alignment carries ten.

Fifty-one kilovolts of difference buys nothing, and five kilovolts of difference at the wrong edge of a band costs four feet. The statute's voltage bands are its own, they are not the ones any other rule uses, and everything else in the section turns on which of the three a conductor falls into.

The statute, in one paragraph and three lines

PRC 4293 sits in Chapter 3 of Part 2 of Division 4, alongside the pole firebreak in PRC 4292, and it reads:

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 trimmed 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.

The section has been in that form since it was amended by Stats. 1976, Ch. 1300, the same chapter that produced the current text of PRC 4292.

Read it once for shape rather than for numbers and four things fall out. The duty binds the person who owns, controls, operates or maintains the line, not the landowner. It is owed on land described by what grows on it. It is owed in all directions. And the trailing paragraph carries two more requirements that have nothing to do with the three distances above them: a temperature condition, and a felling duty for hazardous and leaning trees.

Three bands, and where the edges fall

The bands are written with inclusive floors and exclusive ceilings, so the edges are exact and they are worth reading as arithmetic rather than as categories.

Operating voltage	PRC 4293	Subdivision
750 volts or less	no requirement, by PRC 4296	none
More than 750 but less than 2,400 volts	no distance specified	none
2,400 up to but not including 72,000 volts	4 feet	(a)
72,000 up to but not including 110,000 volts	6 feet	(b)
110,000 volts and above	10 feet	(c)

A 69 kV line is in (a). A 72 kV line is in (b). A 110 kV line is in (c), not (b), because (c) begins at 110,000 and (b) stops short of it. The two steps in the ladder are therefore at 72,000 and 110,000 volts, and neither of them is a boundary that appears in GO 95 Table 1's own column structure, which breaks at 750 volts, 22,500 volts, 300 kV and 550 kV.

A crew working a subtransmission corridor from a Table 1 column heading will put a 69 kV circuit in the same bracket as a 115 kV circuit. The statute does not.

The band at the bottom is the one that produces arguments. PRC 4296 removes lines of 750 volts or less from Sections 4292 and 4293 entirely, and PRC 4293(a) starts at 2,400 volts. Between those two figures the statute imposes no clearance and grants no exemption. CAL FIRE's California Power Line Fire Prevention Field Guide, 2021 edition, addresses the gap from the other side.

It notes at page 22 that lines carrying up to 750 volts have been found to start fires, and that "it is therefore considered good practice to maintain some clearance on these lines." Good practice, in a guide, is not a distance in a statute.

On a 4 kV system stepped down to a 2.1 kV single phase lateral, the lateral is outside PRC 4293's bands and inside Table 1 Case 14's 48 inches. The record for that span has to say which standard was applied, because only one of them supplies a number.

Note also what the bands are indexed to. The statute says "operating at," not designed for, rated at, or nominally classed as. A 115 kV line energized and operated at 60 kV during a construction cutover is operating at 60 kV while it is in that condition, and the clearance owed is (a)'s four feet.

The reverse is the expensive case. A line built at 60 kV and later reconductored to operate at 115 kV moves from (a) to (c) on the day it is energized at the higher voltage. The four feet the corridor was cleared to on its last cycle is now six feet short.

What radial means, and where the distance is measured from

The statute says "in all directions." 14 CCR 1256, Minimum Clearance Provisions-PRC 4293, says how:

Minimum clearance required by PRC 4293 shall be maintained with the specified distances measured at a right angle to the conductor axis at any location outward throughout an arc of 360 degrees. (See Figure 3 this Article.)

Three phrases, and each one settles something a tape measure otherwise gets wrong.

At a right angle to the conductor axis. Not vertically, not horizontally, and not from the pole. The reference line is the wire itself, wherever it happens to be hanging, so on a span crossing a side slope the measurement plane tilts with the conductor and not with the ground. A limb four feet below a conductor at the pole and four feet below it at midspan is a different distance from the wire in each place, because the wire between those two points is not level.

At any location. Every point along the span, not the closest approach and not the point under the crossarm. The requirement is continuous down the length of the conductor.

Throughout an arc of 360 degrees. The full circle, including the sector directly above the wire. This is the part that field practice most often leaves out, because clearing above a conductor requires either an overhanging limb to be removed at its origin or a top to be reduced, and neither is what a side trim produces.

A span whose sides and underside are clear to four feet and whose canopy closes over the top at two is not four feet clear under 1256. It is four feet clear through roughly 300 of the 360 degrees the regulation names.

Put together, the three phrases describe a cylinder centered on the conductor and following it through its sag. On a 300 foot distribution span at 12 kV, the four foot radius makes that cylinder eight feet in diameter and about 15,000 cubic feet in volume, and the entire volume has to be free of vegetation.

CAL FIRE prints the geometry as Figure 12 in the 2021 Field Guide, at page 38, captioned as the PRC 4293 and 14 CCR 1256 conductor clearance example. That figure is the fastest way to settle a disagreement in the field about whether the space above the wire counts.

The clearance has to hold in positions nobody is standing in

A reading is taken at one moment, in one set of conditions. PRC 4293 and 14 CCR 1256 between them require the clearance to survive three sets of conditions that will not be the ones the inspector is standing in.

The statute supplies the first: the distance must be great enough to furnish the required clearance at any position of the conductor "when the adjacent air temperature is 120 degrees Fahrenheit, or less." Adjacent air temperature, not conductor temperature. That distinction matters because the other clearance regimes on a transmission span work the other way.

NERC's Minimum Vegetation Clearance Distance is derived at the conductor's own rated or operating temperature, which on a loaded line runs far above ambient. PRC 4293 fixes the air at 120 degrees and lets the conductor's position follow from it, which is a simpler test and a different one, and a span evaluated only against a conductor-temperature model has not been evaluated against this clause.

14 CCR 1256 supplies the other two, as the two things the minimum clearance shall include:

(1) any position through which the conductor may move, considering, among other things, the size and material of the conductor and its span length; (2) any position through which the vegetation may sway, considering, among other things, the climatic conditions, including such things as foreseeable wind velocities and temperature, and location, height and species of the vegetation.

The second clause is the one that changes what a measured number means, because it puts the tree's movement inside the clearance rather than outside it. Four feet to a rigid interior live oak trunk and four feet to the tip of a flexible bay laurel standing on the windward side of the same span are not the same compliance position. 14 CCR 1256(2) names the species and the foreseeable wind as things to consider in deciding that.

The practical consequence is a documentation one. A clearance figure recorded without the ambient temperature and the wind at the time of reading cannot be tested against either the statute's 120 degree clause or 1256's sway clause by anyone who was not there.

Two numbers beside the distance, taken from the same handheld the crew already carries, are what make the reading checkable a year later. What else a working clearance record holds is its own subject; the part PRC 4293 contributes is that the conditions are not context, they are part of the measurement.

Which conductors, and which hardware

GO 95's vegetation cases are written for bare line conductors. PRC 4293 uses a different phrase, and it is broader in one direction and narrower in another: the clearance runs between all vegetation and "all conductors which are carrying electric current."

Narrower, because a conductor not carrying current is outside the phrase on its face. A de-energized and grounded circuit awaiting reconductoring is not a conductor carrying electric current while it is in that state. The moment it is re-energized the clearance is owed again, and nothing in the statute gives a grace period for growth that accumulated while the line was out.

Broader, because "conductor" is a defined term and the definition is not limited to wire. 14 CCR 1251 defines it as "connector, a wire, or a combination of wires, and/or any other appliance designed and manufactured for use in the transmission and distribution of electrical current," and defines connector in turn as "a device approved for energized electrical connections."

Energy carrying hardware is inside the definition, which 14 CCR 1257(a)(3) confirms from the other direction when it describes primary distribution equipment as "conductor and energy carrying hardware, generally less than 35 kilovolts."

So the four feet is owed from the jumper looping around a fused cutout, from the cutout's own energized parts, and from the tap conductor leaving the connector, on the same terms as from the phase wire in the middle of the span. On a distribution tap, that is frequently the tightest point on the whole structure.

The jumpers hang lower than the phase, they sit closer to the pole, and the tree that was pruned back from the span was pruned to a line drawn along the conductor rather than around the hardware. It is also the point where a pole is likely to be a subject pole and to carry a ten foot firebreak at its base at the same time, measured from a different origin, to a different standard, in the same visit.

The other duty in the same section

The trailing paragraph of PRC 4293 carries an obligation with no distance in it, no voltage band, and no relationship to the three subdivisions above it:

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.

Four categories of tree, one of which is defined by lean rather than by condition, and a duty stated as shall. CAL FIRE's 2021 Field Guide is explicit at page 21 about how far it reaches: the requirement "is independent of the clearance distances identified above and in some cases, may even extend beyond the easements for the utility."

That last clause is the one to think about before a cycle is scoped, because it means the strike zone for this half of the statute is set by tree height and lean, not by the width of the right of way.

Take a 90 foot gray pine standing 60 feet off the centerline of a 12 kV span, sound at the base, with a pronounced lean toward the line and a dead top. Under the clearance half of PRC 4293 the tree raises nothing at all: it is 60 feet from the conductor and the requirement is four.

Under the trailing paragraph it is squarely in scope on two independent grounds, the dead portion and the lean, and the required action is felling, cutting or trimming to remove the hazard rather than a trim to a distance.

Two features of the paragraph are worth marking against the clearance duty beside it. It is not conditioned on the utility's knowledge, where the Commission's overhang provision begins on actual knowledge and is written as should. And it survives the covered conductor relief in PRC 4294.

That section's first sentence removes the clearing requirement where self-supporting aerial cable is used. Its second sentence separately requires the removal of forked trees, leaning trees and any other growth which may fall across the line and break it. What makes a tree a hazard tree in the first place, and what authority exists to take one down without waiting, are separate questions with their own answers.

When it applies, and to which structures

Three limits sit outside the statute's text, and one regulation decides something the statute leaves entirely open.

14 CCR 1252 makes the standing area determination for State Responsibility Areas, and 14 CCR 1253 supplies the fire season limit, county by county, on the Director's posted declaration.

Both reach PRC 4292 through 4296 together, so the same area and season tests that gate the pole firebreak gate the conductor clearance, and what a reading taken outside the declared season is worth is the same question on both halves. Outside the State Responsibility Area the statute still binds on its face and the necessary determination belongs to the agency with primary fire protection responsibility for the area, which 1252 does not make for them.

Where the boundary itself is the question, two short regulations answer it, and they answer it in the utility's disfavor. 14 CCR 1252.2 puts the boundary at the center line where it follows roads, highways, streets, railroads, streams, canals or rivers. 14 CCR 1252.3 goes further:

Where the boundaries of the area described in 14 CAC 1252 are on section, township or range lines, or on powerline rights-of-way, the poles, towers and conductors located thereon are within the area described.

A right of way that forms the State Responsibility Area boundary is inside the area, along with everything standing on it. A boundary drawn along a section line puts the poles on that line inside as well. So the answer to "is this span in the SRA" is not resolved by looking at which side of the line the structure sits on when the line runs through the structure.

14 CCR 1252.1 adds the corresponding duty running the other way: when the Board revises State Responsibility Area boundaries under PRC 4125 to 4128, the Director forwards a legal description of the change to the electric utilities serving the affected areas. That legal description is a dated document arriving at a named utility, which makes it evidence of when a corridor entered the area. Which land sits in which responsibility area is its own subject and a prerequisite to any finding here.

Finally, 14 CCR 1258 answers what the statute does not say about structures. Where conductors and subordinate elements are fastened to living, sound trees, commonly called tree lines, the requirements of PRC 4292 and 4293 apply the same as to a pole or tower line. The tree carrying the conductor is the structure, and the clearance is still owed from the conductor outward through 360 degrees.

The exits the statute names

PRC 4293 opens by excepting Sections 4294 to 4296, and 14 CCR 1257 adds more. Every one of them is a claim the file has to be able to prove, not a category the span falls into by looking at it.

PRC 4294 removes the clearing requirement where self-supporting aerial cable is used, and keeps the removal duty for growth that may fall across the line and break it. PRC 4295 relieves a person who lacks the legal right to maintain the clearing, and does not require entry onto or damage to another's property without consent, which is a test of legal right rather than of effort. Where a refusal ends and the obligation resumes is worth settling before the file is built. PRC 4295.5, added by Stats.

2018, Ch. 641 (AB 2911), effective January 1, 2019, runs in the other direction. It permits traverse of land after notice and an opportunity to be heard, in order to prune to Section 4293 clearances and to abate hazardous, dead, rotten, diseased or structurally defective live trees.

Its clearance language points back here: the clearances obtained are at the utility's full discretion "but shall be no less than what is required in Section 4293," which makes this statute the floor under a discretionary pruning specification. What that right of entry does and does not authorize is its own page. PRC 4296 sets the 750 volt floor.

14 CCR 1257 carries the rest:

• Intact insulated tree wire.

• Intact insulated self-supporting aerial cable.

• Conductors supported by sound and living tree trunks stripped of dead or decadent branches.

• The agricultural and non-propagating areas listed in 1255(c).

• The Exempt Trees regime, with its arborist confirmation, annual inspection, and July 1 database report to CAL FIRE.

What each of those costs to hold belongs to that section's own page.

One caution about which text of 1257 is being read. The 2021 Field Guide reprints 1257 at page 35 in a form that carries only the conductor and area exemptions, without the Exempt Trees subsection at (a)(3) and without subsection (b).

The operative regulation has both: (a)(3) was repealed and re-adopted in its current form on February 8, 2012, and (b) withholds every exemption from Hazard Trees as identified on pages 1-20 through 1-24 of the Department's November 2008 Field Guide. A utility that built its exempt conductor argument from the guide's reprint has built it from a superseded text, and the annual reporting obligation attached to (a)(3) does not appear in that reprint at all.

The last exit is the one in the statute's own final sentence: the Director, or the agency with primary fire protection responsibility, may permit exceptions "based upon the specific circumstances involved." That is a decision by a named official on stated facts, and the artifact it produces is a letter. Absent the letter, the exception has not been permitted.

What the record has to name

A PRC 4293 span record has to close two obligations, not one, and they are found by different methods.

The clearance entry needs the subdivision, not just the distance: 12 kV, subdivision (a), four feet required. Add the measured radial clearance at the closest approach, the location along the span, the ambient temperature and wind at the reading, the date, and the county's fire season status on that date. Every one of those is checkable against the statute's 120 degree clause, 14 CCR 1256's movement and sway clauses, and the seasonal limit by someone reading the file later. A distance standing alone is checkable against none of them.

The hazard tree entry is a separate line and it does not carry a distance at all. It names the tree, its position relative to the line, the ground it is in scope on, dead or decadent or rotten or weakened or leaning, and the action taken: felled, cut or trimmed. A span whose file records a clearance and is silent on the trees leaning toward it has answered the first sentence of the trailing paragraph and not the second.

The inspection method is worth recording alongside, because CAL FIRE's own guide says the two halves are not equally visible from the same platform. The 2021 Field Guide observes at page 16 that aerial inspection is particularly effective at spotting leaning or dead trees that are not immediately adjacent to the line.

From the air, though, "it is rather difficult to identify small items of hardware, conductor clearances or less obvious tree defects." An overflight is a reasonable way to find the trailing paragraph's trees and a poor way to close a radial clearance finding. Which inspection type can actually close which finding is the question that record answers.

Where an exemption is claimed, the file holds the artifact rather than the label.

Exemption claimed	The artifact the file holds
1257(a)(1)	the photograph of the covering intact at the point of contact
1255(c)	the cultivation status
an Exempt Tree	the arborist's or forester's confirmation and the database coordinate
a specific-circumstances exception	the Director's letter
PRC 4295	the parcel-level evidence of withheld consent

An exemption asserted without its artifact reads to an evaluator as an open finding under a different name. On this statute an open finding is exposure under PRC 4021. That section makes the negligent or willful omission of an act required by Chapter 2 through Chapter 6 of Part 2 of Division 4 a misdemeanor. Which body will look at it, and what each one can do is worth knowing before the audit rather than during it.

Further reading

• PRC 4292: the ten-foot firebreak around a pole, and what counts: The other half of the same statute, measured from the pole instead of the conductor.

• GO 95 Rule 35 and PRC 4293: two rules, two different clearances: What happens on a span the Commission and CAL FIRE both reach.

• Title 14 CCR sections 1250 to 1258: the implementing rules: The regulations that operate PRC 4292 through 4296, section by section.

Frequently asked questions

What clearance does PRC 4293 require?

Four feet for a line operating at 2,400 or more volts but less than 72,000, six feet at 72,000 or more but less than 110,000, and ten feet at 110,000 or more. The bands are the statute's own, and they do not match the voltage classes GO 95 Table 1 uses. A 69 kV subtransmission circuit sits in the four foot band alongside a 12 kV feeder.

Is the four feet measured sideways, or in every direction?

In every direction. 14 CCR 1256 requires the distance to be measured at a right angle to the conductor axis at any location outward through an arc of 360 degrees, which includes the space directly above the wire. The statute's own phrase is 'in all directions.' Clearing the sides and the underside of a span leaves the top of the cylinder uncleared and the span noncompliant.

Does PRC 4293 require anything besides a clearance distance?

Yes, and it carries no distance. The same section requires that dead trees, old decadent or rotten trees, trees weakened by decay or disease, and trees or portions of trees leaning toward the line that may contact it from the side or fall on it be felled, cut, or trimmed. CAL FIRE's 2021 Power Line Fire Prevention Field Guide states at page 21 that this requirement is independent of the clearance distances and may extend beyond the utility's easements.

Does a clearance measured on a cool, still morning satisfy PRC 4293?

Not by itself. The statute requires the distance to hold at any position of the conductor when the adjacent air temperature is 120 degrees Fahrenheit or less, and 14 CCR 1256 adds any position through which the vegetation may sway under foreseeable wind velocities. A reading with no ambient temperature and no wind condition recorded beside it cannot be tested against either clause.