Size Free — Cable

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.

| 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 | cable size

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. Disclaimer: This guide is for informational purposes

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. | Gauge (AWG) | Max Amps (Breaker) |

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.

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.