5 Things to Know About Hot Extension Cords and Current Capacity

Ambient temperature directly affects ampacity Extension cords are rated for a standard temperature of 30°C (86°F). In hotter conditions, the cord cannot shed heat effectively and must carry less current to avoid overheating.

Derate by about 10% for every 10°C above 30°C For common cords rated 60°C or 75°C, this rule of thumb applies. A 15-amp cord in direct sun or a hot attic may only safely handle 12 amps.

Hot environments create a fire hazard Running a cord near its limit in high heat is not a theoretical risk. It can melt insulation and cause a fire.

Keep cords out of hot environments when possible If you are pushing a cord near its rated limit, avoid placing it on black roofs, in attics, or in direct sunlight.

Go up one gauge thicker if you must use a cord in heat If you need to run a cord across a hot surface, choose a thicker gauge than you think you need. Do not gamble on “probably fine.”