ELECTRICAL SAFETY ON CONSTRUCTION SITES: A WORKER'S GUIDE

← Back to Blog

Electrocution is one of the "Fatal Four" — the four leading causes of death on construction sites across North America, alongside falls, struck-by incidents, and caught-in/between hazards. In Canada, electrical contact accounts for approximately 13% of construction fatalities. The Electrical Safety Authority (ESA) in Ontario investigates dozens of serious electrical incidents on construction sites every year, and many more go unreported as near-misses.

What makes electrical hazards particularly dangerous is that they are often invisible. You cannot see voltage. You cannot smell current. A wire that looks dead may be live. A puddle of water near a power tool can become a conductor. This guide covers the electrical hazards you are most likely to encounter on a construction site and how to protect yourself.

Overhead Powerline Clearances

Contact with overhead powerlines is one of the most common causes of electrocution on construction sites. Cranes, boom lifts, concrete pump trucks, excavator booms, scaffolding, ladders, and even long pieces of material like rebar, conduit, or aluminum siding can reach powerlines.

Ontario Regulation 213/91 (Construction Projects), Section 188 sets out minimum approach distances for overhead powerlines:

• 750 volts to 150,000 volts: No equipment, material, or worker may come within 3 metres (10 feet) of the powerline.
• 150,001 volts to 250,000 volts: Minimum clearance is 4.5 metres (15 feet).
• Over 250,000 volts: Minimum clearance is 6 metres (20 feet).
• If voltage is unknown: Treat it as over 250,000 volts and maintain 6 metres clearance until the utility confirms the actual voltage.

These distances apply to all parts of any equipment at full extension, including load lines, boom tips, and anything being hoisted. Wind, boom bounce, and cable swing must be factored in — the clearance distance must be maintained at all times, not just when the machine is stationary.

Before any work begins near overhead powerlines, the constructor must contact the utility company. Options include de-energizing and grounding the lines, installing protective barriers, or establishing a safe work zone with flagging, signage, and a dedicated signal person. Never assume a powerline is dead. Even lines that appear unused may be energized.

Ground Fault Circuit Interrupters (GFCIs)

A GFCI detects when electrical current is flowing through an unintended path — like through your body to ground — and cuts the circuit in milliseconds, before the current can cause serious injury or death. On construction sites, GFCIs are critical because the conditions that make electrocution more likely (wet surfaces, damaged cords, unfinished wiring, temporary power) are present every day.

Ontario Regulation 213/91, Section 195 requires that every temporary power receptacle on a construction project be protected by a GFCI. This applies to all cord-connected tools and equipment used by workers.

• Test GFCIs before each use: Press the test button. The GFCI should trip and cut power. Press the reset button to restore power. If the test button does not trip the GFCI, do not use that outlet — report it immediately.
• Use portable GFCIs: If the power source does not have built-in GFCI protection, plug a portable GFCI device into the outlet before connecting your tool. These are inexpensive and widely available.
• Never bypass a GFCI: If a GFCI keeps tripping, there is a reason — the tool or cord has a ground fault. Find and fix the problem. Do not defeat the safety device.

Never assume a circuit is dead. Even after you flip the breaker, use a voltage tester to confirm zero energy before touching any conductor. Assumptions about de-energized equipment kill electrically qualified workers every year.

Lockout/Tagout

Lockout/tagout (LOTO) is the procedure for ensuring that electrical equipment is completely de-energized and cannot be accidentally re-energized while workers are performing maintenance, repair, or construction work on or near it. LOTO failures are a leading cause of electrical injuries in construction.

• Identify all energy sources: Electrical equipment may have multiple sources of energy — main power, backup power, stored energy in capacitors, battery backup systems. All sources must be identified and controlled.
• De-energize at the source: Open the disconnect switch or circuit breaker that supplies power to the equipment. Verify that the equipment is de-energized using a voltage tester rated for the expected voltage. Never rely on simply flipping a switch — test to confirm zero energy.
• Lock and tag: Apply a personal lock to the disconnect so it cannot be closed. Attach a tag with your name, date, and reason for the lockout. Each worker in the danger zone applies their own lock — the equipment cannot be re-energized until every lock is removed by the person who placed it.
• Never remove someone else's lock: If a worker leaves the site with their lock still on, follow your company's documented procedure for lock removal. This typically involves the supervisor verifying the worker is clear and documenting the removal.

Working in Wet Conditions

Water and electricity are a lethal combination. Construction sites are frequently wet — rain, snow, groundwater seepage, concrete pouring, pipe testing, and simple puddles create conditions where electrical hazards multiply.

• Never use electrical tools or equipment in standing water unless they are specifically rated for wet conditions and GFCI-protected.
• Inspect cords and plugs: Damaged insulation, cracked plugs, missing ground prongs, and taped-together extension cords are exponentially more dangerous in wet conditions. Remove damaged cords from service immediately.
• Keep connections elevated: Extension cord connections (where two cords join) should be raised off the ground and kept dry. Water pooling around a cord connection can create a ground fault.
• Wear appropriate PPE: Rubber-soled boots provide some insulation from ground faults. When working in wet electrical environments, rubber insulating gloves rated for the voltage may be required.
• Temporary power distribution: Temporary panels, spider boxes, and power distribution units on site must be rated for outdoor use (NEMA 3R or better) and positioned on stable, dry surfaces away from drainage paths.

Tool and Equipment Inspection

Damaged tools and cords are one of the most common causes of electrical injury on construction sites. A daily visual inspection takes seconds and can prevent a serious incident.

• Power cords: Check the entire length for cuts, abrasion, exposed conductors, kinks, and damage to the outer jacket. Check the plug — the ground prong must be intact. If the ground prong is missing or bent, take the cord out of service.
• Tool housings: Cracks in the housing of a power tool can expose internal wiring. If the housing is cracked or damaged, do not use the tool.
• Double-insulated tools: Tools marked with a double-insulated symbol (square within a square) have an extra layer of insulation and do not require a ground prong. But they still need intact housings and cords to maintain that protection.
• Extension cords: Use only cords rated for construction use — heavy-duty, with a ground conductor, and rated for the load. Indoor-rated extension cords are not acceptable on construction sites.

Arc Flash Awareness

An arc flash is an explosive release of energy caused by an electrical fault — a short circuit that ionizes the air and creates a plasma fireball. Arc flash temperatures can reach 19,000°C (four times the surface temperature of the sun). The blast wave can throw workers across a room. Arc flash is primarily a concern when working on or near energized electrical panels, switchgear, and distribution equipment.

• Stay out of the arc flash boundary: Energized electrical panels should have arc flash labels indicating the incident energy level and the minimum approach distance. Do not open energized panels unless you are a qualified electrical worker with appropriate arc-rated PPE.
• Never work on live equipment: The Ontario Electrical Safety Code and CSA Z462 (Workplace Electrical Safety) require that equipment be de-energized before work begins, with very limited exceptions that require specific training and PPE.
• Report damaged panels: If you see a panel with missing covers, burn marks, a burning smell, or buzzing sounds, stay away and report it immediately. These are signs of an impending arc flash.

What to Do if Someone Is Being Electrocuted

If you see a co-worker in contact with a live electrical source, your instinct will be to grab them and pull them away. Do not do this. If you touch someone who is in contact with live electricity, the current will flow through them and into you. Now there are two victims instead of one.

• Cut the power: If you can safely reach the disconnect switch, breaker, or plug without touching the victim or the energized source, de-energize the circuit immediately.
• Separate without touching: If you cannot cut the power, use a dry, non-conductive object — a dry wooden board, a rubber mat, a dry rope — to push or pull the victim away from the source. Do not use anything metal, wet, or made of carbon fibre.
• Call 911: Electrical injuries cause internal damage that is not visible. Even if the victim appears fine after being separated from the source, they need immediate medical evaluation. Electrical current can disrupt heart rhythm, damage internal organs, and cause burns deep inside the body.
• Begin CPR if needed: If the victim is not breathing or has no pulse after being separated from the electrical source, begin CPR immediately and continue until paramedics arrive.

The Bottom Line

Electricity does not give warnings and it does not give second chances. Respect the clearance distances around powerlines. Test your GFCIs. Lock out before you work. Inspect your cords and tools every day. Stay aware of wet conditions. And know what to do if something goes wrong. These are not complicated procedures — they are the basics that keep you alive on the job.