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Breaker Size Calculator

Find the breaker size for a load from its watts or amps, applying the 125% rule for continuous loads, and the minimum copper wire.

Load (watts)

Voltage

Continuous (3 h+)?

How to use it

Enter the load watts (nameplate).
Continuous loads (EV charging, water heaters, baseboard heat) use 125%.

How it works

Amps = W ÷ V; breaker ≥ amps × 1.25 for continuous loads, rounded up to the next standard size (15, 20, 25, 30, 35, 40, 45, 50, 60, 70, 80, 90, 100…).

FAQ

What size breaker for a 48 A EV charger?

48 A × 125% = 60 A breaker with 6 AWG copper (75 °C terminals).

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