Why your extension cord might be a fire hazard
Extension cords have a gauge — a wire thickness rating — and most people never look at it. The wrong cord for the wrong load generates heat in the wire, and enough heat starts fires. This is one of the most common causes of residential electrical fires.
How AWG works (backwards)
AWG stands for American Wire Gauge. The number and the thickness have an inverse relationship:
- Lower number = thicker wire = more capacity
- Higher number = thinner wire = less capacity
A 10 AWG cord can handle more current than a 16 AWG cord. This is counterintuitive and people get it wrong constantly.
| AWG | Max Amperage | Common Use |
|---|---|---|
| 10 | 30A | Heavy shop tools, large appliances |
| 12 | 20A | Power tools, high-draw appliances |
| 14 | 15A | General use, most household items |
| 16 | 13A | Lamps, electronics, light loads |
| 18 | 10A | Small electronics, phone chargers |
Why thin cords + high loads = fire
Wire has resistance. Current through resistance generates heat. The thinner the wire, the higher the resistance, the more heat generated per amp flowing through it.
A space heater draws 12–15 amps. A hair dryer draws 12–16 amps. If you run either through a 16 AWG cord designed for 13A, the cord becomes a resistive heater. The insulation melts. The heat transfers to carpet, furniture, or wall. The cord may look fine on the outside while the insulation inside is already failing.
Undersized cords also cause voltage drop — your device doesn't get the voltage it needs, runs inefficiently, draws more current, and the problem compounds.
Length matters too
Longer cords have more total resistance. As cords get longer, they need to be thicker to carry the same load safely. The rating on the label is usually for a specific length:
- A 25-foot 16 AWG cord: safe for light loads
- A 100-foot 16 AWG cord: dangerous for the same load the 25-foot handled fine
If you need a long cord for a high-draw tool or appliance, go up in gauge (down in number).
The cords that come with appliances
The power cord attached to a space heater, hair dryer, or shop vac is rated for that appliance. When you plug it into an extension cord, you're adding a length of wire that may not be rated for the same load. The appliance cord is fine — the extension cord is the weak link.
General rules:
- Don't run space heaters or hair dryers through extension cords if you can avoid it
- If you must, use at minimum 14 AWG, preferably 12 AWG
- Never run an extension cord under a rug (you can't see it heating up)
- Never coil an extension cord while it's under load (coiling concentrates heat)
- Don't staple or nail extension cords to walls — that damages the insulation
Reading the label
Look for the AWG number on the cord itself. It's usually printed or molded into the jacket. Also check for UL or ETL listing marks — these confirm it was tested to safety standards. Cheap unrated cords from discount bins may have no safety certification at all.
For outdoor use, cords must be marked for outdoor use (usually orange, marked "W" or "W-A" in the designation).
Quick reference
- Lower AWG = thicker = more capacity
- 16 AWG max for lamps and light electronics
- 14 AWG minimum for general household use
- 12 AWG for power tools, space heaters, high-draw loads
- Never under rugs. Never coiled under load. Never daisy-chained.