Safety
The Wrong Extension Cord Gauge Gets Hot Enough to Start a Fire
Running a space heater on a light-duty extension cord is one of the most common preventable causes of house fires in cold months.
Measurements in this article
Wire gauge determines resistance, and resistance under load generates heat. A cord rated for 13 amps asked to carry the 15 amps a space heater draws will run measurably hotter than one properly rated, especially over long runs where resistance adds up.
Coiling a cord that's still under load compounds the problem: the tightly wound loops trap heat against each other instead of letting it radiate away, which is why a coiled cord can get noticeably warmer than the same cord run flat.
| Amp draw | Minimum cord gauge (25 ft) |
|---|---|
| 7 amps | 16 AWG |
| 10 amps | 14 AWG |
| 15 amps | 12 AWG |
| 20 amps | 10 AWG |
Written and reviewed by Jim Vernon, editor of Home & Garden Answers · Last updated
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