Extension Cords & Temporary Cords

Extension cords on jobsites get run over, pinched in doors, dragged over sharp edges and soaked in water. A damaged cord is one of the most common causes of jobsite shocks.

• Construction
• General Industry

Use the right cord

• Hard-service or extra-hard-service cords. Look for jacket markings like S, SO, ST, SJ, SJO, SJT, SJOOW or SOOW.
• Three-wire, grounded cords with a ground pin.
• Heavy enough gauge for the tool and the length. Long runs and big tools need a lower gauge number (thicker wire), such as 12 or 10 AWG.
• Rated for outdoor use (“W”) when used outside or in wet areas.

Reading the jacket

The letters printed on the cord jacket tell you how tough it is:

Example: SJOOW is a hard-service, oil-resistant, outdoor-rated cord. Light-duty household cords (like SPT “lamp cord”) don’t belong on a jobsite.

Size matters

A cord that’s too thin for the tool or too long overheats and starves the tool of voltage. Check the tool’s amp rating and the manual. A common guide for 120-volt tools:

Lower numbers mean thicker wire. A cord that feels warm in use is a warning sign. Uncoil cords fully before running high loads, since coiled cords can overheat.

Inspect before each use

• Outer jacket not cut, cracked, crushed or worn through (no inner wires showing)
• Ground pin present and not bent
• Plug and connector not cracked, melted or loose
• No splices except those done properly, and no electrical tape “repairs” on the jacket
• Strain relief at both ends holds the jacket in place

Remove damaged cords from service immediately. Cut the plug off or tag it if your company policy says so.

Protect cords on site

• Run cords overhead or along walls, out of walkways and traffic.
• Use cord ramps where vehicles or carts must cross them.
• Plug into GFCI protection.
• Unplug by the plug, not the cord.

• Don’t run cords through doorways, windows or holes where they can be pinched, unless protected.
• Don’t fasten cords with staples or nails, or hang them from nails.
• Don’t daisy-chain cords or power strips.
• Don’t use cords as a substitute for permanent wiring.
• Don’t lift or lower tools by the cord.

Assured grounding programs and color codes

Some construction employers use an assured equipment grounding conductor program instead of, or along with, GFCIs. Under that program, a competent person tests every cord, receptacle and cord-connected tool for ground continuity and correct wiring:

• Before first use
• Before returning to service after any repair
• After any incident that could have damaged it
• At least every 3 months (6 months for fixed cords not exposed to damage)

Many sites mark tested cords with a colored tape for each quarter. If your cord’s tape color is out of date, don’t use it. See GFCI Protection.

Storing cords

• Coil loosely in an over-under loop or on a reel; don’t wrap tightly around your arm.
• Keep cords out of the sun, away from oil and chemicals, and off the ground of a wet trailer.
• Don’t store cords in a heap where they get kinked or crushed.

Last updated: October 1, 2026