| Gauge (AWG) | Max Amps (Breaker) | Typical Use | | :--- | :--- | :--- | | | 15 Amps | Lighting circuits, general outlets (bedrooms) | | 12 | 20 Amps | Kitchen small appliances, bathroom outlets, garages | | 10 | 30 Amps | Water heaters, window AC units, RV hookups | | 8 | 40 Amps | Small sub-panels, oven ranges | | 6 | 55 Amps | Large sub-panels, EV chargers, central AC |
Disclaimer: This guide is for informational purposes. Electrical work can be lethal. Always consult a licensed electrician and check your local building codes before beginning any electrical project. cable size
Your extension cord must be as thick as the wall wire feeding the outlet. If your tool draws 15 amps, you need a 14 AWG cord (or thicker). How to Calculate the Right Size If you’re installing a new circuit, use the 80% rule (Continuous Load Rule). If a device runs for more than 3 hours (lights, EV charger, heaters), you can only load the breaker to 80% of its rating. | Gauge (AWG) | Max Amps (Breaker) |
Note: Aluminum wire (common for service entrances) needs to be 1-2 sizes LARGER than copper to carry the same load. We see it all the time: A homeowner buys a massive 10,000-watt space heater and plugs it into an extension cord that looks like a lamp cord. The heater tries to draw 40 amps. The 18-gauge cord is rated for 7 amps. Your extension cord must be as thick as
The result? The cord becomes a toaster element. It doesn't always trip the breaker (because the short isn't happening yet), but the rubber melts, the wires touch, and then the breaker trips—often too late.
If your cable is too small for the load, that heat doesn’t just dissipate—it builds up, melts the insulation, and starts a fire. In fact, undersized wiring is one of the leading causes of electrical house fires.
When you flip a light switch or plug in a space heater, you expect the electricity to just work . But behind your drywall, a silent battle is taking place. The copper (or aluminum) inside your cables is resisting the flow of current, and that resistance creates heat .