Power Line Hazards in Tree Work

Electricity kills tree workers, and you do not have to touch a wire with your hands for it to happen. A branch swings into a line. A wet rope carries current. A ground worker leans on a truck whose boom has touched a conductor. The worst part of this hazard is that it gives no warning. Reading this does not make you qualified to work near energized lines. Only proper training, and an employer who documents that you are qualified, can do that. If you have not been trained for this work, your job is simple: recognize the hazard, stay back, and call for the right crew.

What You Will Be Able to Do

• Explain which OSHA rules and which ANSI Z133 levels apply to a job
• Work out the approach distance for an unqualified worker
• Name the ways current reaches a tree worker
• Plan a job near lines, including who to call
• Explain the special rules for line-clearance work and storm work
• Respond safely to an electrical contact

Which Rules Apply

Several sets of rules can cover the same tree.

• OSHA 29 CFR 1910.333 sets general rules for work near overhead lines, including the distance for unqualified workers.
• OSHA 29 CFR 1910.269 covers line-clearance tree trimming, which is work done to clear space around power lines.
• ANSI Z133 is the industry safety standard. OSHA's rules are the law. Z133 is a voluntary standard, but it is widely treated as accepted industry practice. The current edition is Z133-2026.
• State rules and utility rules can be stricter. Some states have overhead line laws that require you to notify the utility before you work near high-voltage lines.

Your employer has to know which ones apply and train you on them. Read the current Z133 text itself. Its approach distances and details are not reproduced here.

Who May Do What

Z133-2026 sorts arborists by their electrical qualification. The Tree Care Industry Association reports these four levels.

The new edition removed the old "incidental line clearance" qualification. TCIA also reports that a Level 3 arborist may work within 10 feet of lines above 35,000 volts only under an abatement plan made with the utility. A level is a training and employer decision, not a job title. A worker does not reach a level by being experienced around wires.

The 10-Foot Rule

For an unqualified person, OSHA sets a clear line. You, and any conductive object you are holding or using, must stay at least 10 feet from an unguarded energized overhead line up to 50,000 volts to ground. Above that, add 4 inches for each 10,000 volts over 50,000.

That rule covers the longest thing you can reach. A pole saw, a ladder, a rope, and a limb you are cutting all count. Vehicles and equipment that can raise a part of their structure near a line have their own 10-foot clearance.

Worked example. A distribution line is rated 12,470 volts between phases. That is about 7,200 volts to ground, so the distance is 10 feet. A transmission line is rated 230,000 volts between phases. That is about 133,000 volts to ground. It is 83,000 volts over the 50,000-volt mark, so you add 8.3 x 4 inches, or about 33 inches. The distance is about 12 feet 9 inches.

You do not work out the voltage from what a line looks like. The utility tells you. If you cannot get the voltage, treat it as the highest possible, and keep away.

How Current Reaches You

A green tree can conduct enough current to kill you. So can a dead one if it is wet. Bark and leather gloves do not protect you.

Step and Touch Potential

When current goes into the ground, the voltage falls off as it moves out from that point, like ripples in water. If your feet stand at two different voltages, current can flow up one leg and down the other. That is step potential. If you touch an energized object while standing on the ground, current can flow through your body. That is touch potential. This is why people near a downed line or a hot truck get hurt even when they never touch the wire.

Reading the Lines

Before anyone leaves the ground, look up and walk the site. Treat every line as energized.

• Primaries are the high-voltage lines, usually at the top of the pole.
• Secondaries and service drops carry lower voltage to buildings. They can still kill you. Do not count on the covering of a service drop as insulation, because it can be worn or damaged.
• Neutral and communication lines usually sit lower. They can become energized by a fault, so do not treat them as safe.
• Hidden lines run through the crown, and they are easy to miss in full leaf.

Lines and Limbs Both Move

The distance you measure on a calm morning can shrink without you touching anything.

• Lines sag in hot weather and when loaded with power.
• Wind swings both the wire and the branches.
• A limb lifts when weight comes off it. Cutting the end of a long limb can make the rest spring up into a line above it.
• Pieces rotate as they fall.
• Rope whips.

Plan the distance for the worst moment of the cut.

Planning the Job

If any part of the work, including what you cut, could come within the approach distance, stop and do this before you start.

1. Identify the lines and get the voltage from the utility.
2. Ask the utility what it can do. It may de-energize the line, install covers, or send its own line-clearance contractor. Asking early matters, because it takes time to schedule.
3. Confirm who is qualified. If nobody on the crew has the right qualification, the crew does not do that part of the job.
4. Get any notice or permit your state or city requires.
5. Add it to the job briefing, and mark the limit on site.
6. Plan each cut. Know which way it will fall, and how you will keep it clear of the line.

A covered line is not a safe line. Only the utility can tell you that a line is de-energized, and for how long. Until you have that word, it is energized.

Worked example. A homeowner wants a maple trimmed. One limb reaches within 6 feet of a service drop, and the rest of the tree is well clear. Your crew is Level 1. You trim the part of the tree that stays beyond 10 feet, including the reach of your tools and the limbs you cut. You stop short of the limb near the drop. You tell the homeowner why, and call the utility to arrange for the line to be disconnected or covered, or bring in a qualified crew. Nobody on your crew reaches in "just this once".

Line-Clearance Work

OSHA defines line-clearance tree trimming as pruning, repairing, removing, or clearing trees within 10 feet of electric supply lines and equipment, for voltages to ground of 50,000 volts or less, plus the same 4 inches per 10,000 volts above that. A line-clearance tree trimmer is someone who, through training or experience, knows the special methods and hazards of this work.

Under 1910.269, the employer has to make sure line-clearance trimmers who are not qualified electrical workers follow these rules:

• Find the voltage first. Before anyone climbs, enters, or works around a tree, the employer finds the nominal voltage of lines that pose a hazard. Or it treats all lines as being at the highest voltage present.
• Have a second trimmer. A second line-clearance trimmer must be within normal, unassisted voice range when a trimmer will come within 10 feet of a conductor over 750 volts, when branches being cut are closer to those lines than the distances in OSHA's tables, or when roping is needed to remove branches from those lines.
• Keep the distances. Trimmers keep to the minimum approach distances in OSHA's tables.
• Use insulated tools. Branches touching lines, or inside those distances, may be removed only with insulating equipment. A tool counts as insulated only if it meets the rule and is clean and dry.
• Keep gear back. Ladders, platforms, and aerial devices may not be brought closer than the table distances.

Line-clearance work takes its own training, with a documented qualification. It is not something you pick up on the job by watching.

Aerial Lifts

Insulated booms are tested for specific uses. They only work if they are clean, dry, and inside their test dates. Metal tools, a dirty boom, or a wet rope can bypass them. The lift also does nothing for the person on the ground. Ground crew stay off a truck while the boom is near a line. OSHA's rule also warns workers on the ground to keep clear of the grounding point of equipment that could touch a line.

Storm Work

Storm work is some of the most dangerous tree work there is. Lines are down or tangled in trees. The trees are loaded and twisted. Crews are tired. Under OSHA's line-clearance rule, tree trimming may not go on when weather makes it hazardous in spite of safe work practices, and OSHA's note names thunderstorms in the immediate area, high winds, snow storms, and ice storms. Workers doing storm cleanup must be trained in the special hazards involved.

• A line on the ground may be live, even if it is quiet.
• Lines that look dead can be re-energized without warning by the utility's equipment.
• A home generator can feed power back into a line that the utility thought was off.
• A tree that is lying on a line may be holding that line down under tension.

Do not touch any tree in contact with a line until the utility says it is de-energized and grounded.

Radio Frequency Hazards

Antennas on poles, towers, and rooftops can give off radio frequency energy. Z133-2026 adds awareness training on this. Treat an antenna the way you treat a wire: ask who owns it, and do not work close to it without knowing it is safe.

If Someone Is in Contact

Warning: Rescuers die at electrical contacts. Do not touch the person, the tree, the rope, or the truck. Current may still be flowing through all of them.

1. Stop. Shout for everyone to stay back, and keep them well clear. The ground itself may be energized.
2. Call 911 and the utility. Give the exact location and the pole number if you can see it.
3. Stay clear until the utility confirms the line is de-energized. Do not guess.
4. Then give care. Once it is safe, start CPR and use an AED if needed, and treat burns. A person who has had a shock needs medical care, even if they seem fine.
5. Aerial rescue happens only after the electrical hazard is gone, and only by a trained rescuer.

Vehicles in Contact

If a truck touches a line and you are in it, stay in it. Warn others to keep away. Call for help. Leave only if there is a fire or another danger you cannot stay with. Then jump clear so that you never touch the truck and the ground at the same moment, land with your feet together, and move away with your feet close together, using short shuffles or small hops. Do not go back.

Common Mistakes

Check Your Understanding

1. Nobody can reach the utility, and you do not know the voltage of a wire behind a house. The owner says it is only a house feed, so 10 feet is plenty. What do you do?

You do not take voltage from how a line looks, or from what an owner says. Treat it as the highest voltage it could be, and keep away until the utility tells you.

2. At 7 AM on a cool, calm day, you measure 11 feet between a branch and a wire. By 2 PM it is hot and windy. Your crew is not qualified for work near lines. Can you rely on that measurement?

No. Lines sag in heat, and wind swings both the wire and the branch, so the gap may have shrunk. Plan for the worst moment. If anything could come inside 10 feet, stop and call the utility.

3. A ground worker wants to feed a limb that was resting on a service drop into the chipper. What do you tell them?

Stop. That limb may be energized, and the chipper can carry current to the person touching it. Do not touch it until the utility deals with the line.

4. You are the second person on a line-clearance job. Your partner is about to rope a branch off a 7,200-volt line. Why must you stay within voice range?

OSHA requires it for roping branches from lines above 750 volts. You are there to help and to call for help at once.

5. An aerial lift's boom touches a wire. The driver is in the cab, and a coworker runs over to help. What do you do?

Stop the coworker and keep everyone well back, because the truck and the ground may be energized. Tell the driver to stay in the cab, and call 911 and the utility. The driver leaves only for a fire or another danger they cannot stay with, and jumps clear without touching the truck and the ground together.

Key Takeaways

• Treat every line as energized until the utility says otherwise.
• Unqualified workers stay 10 feet back, and that includes tools and limbs.
• Current reaches you through trees, ropes, tools, trucks, and the ground.
• Only qualified people do work inside the approach distances.
• Lines and limbs move, so plan for the worst moment.
• At a contact, stay back, call, and wait.