Underground Power Lines

Buried power lines can’t be seen, and a shovel, backhoe tooth or drill bit that hits one can cause an explosion of electricity. Digging into an energized cable has killed excavators and operators. Finding the line first, and digging carefully, prevents most strikes.

• Electrical
• Excavation
• Utilities

What’s underground

• Primary lines carry thousands of volts from the utility to transformers. They are deadly on contact and can arc over short distances.
• Secondary and service lines run to buildings at lower voltage, but still enough to kill.
• Street lighting, traffic signal and private feeder cables may not be on utility maps.
• Cables may be in conduit, duct banks or direct-buried, sometimes wrapped with concrete or warning tape above.
• Depth varies. Cables can be shallower than expected after grading or erosion.

Before you dig

1. Call 811 at least a few working days before digging, as your state law requires. The utilities mark their lines for free. See Call 811.
2. Wait for all utilities to respond and look at all marks. Check that every utility has replied.
3. Know the marks. Red paint or flags mean electric power lines, cables, conduit and lighting cables. Yellow is gas, orange is communications, blue is water and green is sewer. See Utility Locators.
4. Check for private lines. Utilities don’t mark lines on private property beyond the meter. Hire a private locator for those. See Private Utility Locating.
5. Look for clues: pad-mounted transformers, pole risers, meters, street lights and ground patches that suggest buried power.
6. Plan the work around the marks. Discuss them with the crew and operator.

Digging near a marked line

• Every state has a tolerance zone around each mark (often about 18 to 24 inches on each side, but the width varies). Check your state law. Inside it, you must expose the line carefully, usually by hand digging or vacuum excavation.
• Hand dig or use vacuum excavation (potholing) to see the line before machines dig nearby. See Hydro-Vacuum Excavation.
• Use a spotter with machines, and slow down near marks.
• Never use a metal probe or bar to find a cable. It can hit and energize.
• Protect the exposed line: keep it supported, don’t strike or pull it, and don’t put weight on it. See Supporting Exposed Utilities.
• Keep marks visible. If they’re erased, stop and call 811 again.

Drilling and boring

Horizontal drilling can hit a line where you can’t see it. Pothole and expose existing lines at crossings and along the path before drilling, and use locators and the tracking equipment. Drill rigs and rods can become energized when they hit a line, and the operator and crew nearby are at risk. See Directional Drilling.

If you hit a power line

1. Stop work. Don’t try to back out or pull the line free.
2. If you’re on a machine, stay in the cab and warn everyone to stay back at least 35 feet. Wait for the utility to say it’s safe. If fire forces you out, jump clear with feet together and shuffle or hop away. See Step & Touch Potential and When Equipment Contacts a Power Line.
3. Call 911 and the utility. Tell them exactly what happened and where.
4. Keep everyone away from the equipment, the load, the hole and anything wet near it.
5. Report every strike, even a minor nick or damage to the coating, because damaged insulation can fail later. Never cover or backfill damaged cable.

Employer duties

OSHA requires employers to find the location of underground utilities before excavating, and to protect workers from them (29 CFR 1926.651(b)). The employer must also train workers and make sure a competent person is in charge. See Utility Strikes.

Before digging, check

• 811 ticket current, and all utilities have responded
• Red marks and other colors identified and discussed with the crew
• Private lines located by a private locator if needed
• Hand digging or vacuum excavation inside the tolerance zone
• No metal probes; spotter assigned for machines
• Strike plan and utility emergency numbers posted

Last updated: October 4, 2026