Electrical
Breaker Size Calculator
Work out the overcurrent protection a load needs, using the 125% continuous-load rule.
Result
Electrical work is life-safety work governed by the NEC or your local code, and must be designed and installed by a licensed electrician. Conductor and overcurrent sizing depends on ambient temperature, conductor bundling, termination ratings, continuous-load rules and more. This is an educational estimate and must never be used as the basis for an installation. The breaker must also be matched to conductor ampacity. A breaker larger than the wire it protects is a fire risk. Motors, welders, air conditioners and transformers have their own sizing rules that override this.
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About this calculator
Why 125% for continuous loads?
Breakers are calibrated at a temperature that assumes intermittent operation. Loads running three hours or more heat the device and its terminations, so the NEC requires 25% extra capacity.
Can I just fit a bigger breaker if it keeps tripping?
No. This is genuinely dangerous. The breaker protects the wire. Fitting a larger one lets the conductor overheat before the breaker trips, which is how electrical fires start. Find the cause instead.
The formula
design current = load current × 1.25 for continuous loads; round up to the next standard device
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