How to use the AC Inrush Current Limit Calculator
The Formula
Motors, transformers, and SMPS draw brief startup current many times higher than running amps. Thermal breaker curves allow short magnetic overload—if inrush exceeds the magnetic trip band, the breaker opens even though steady-state amps are fine.
Practical Example
I_run = P ÷ V. I_peak = I_run × inrush factor. Breaker ≥ max(1.25 × I_run, I_peak ÷ magnetic multiple for curve type). Type B ~5×, Type C ~7.5×, Type D ~12.5× rated current for instantaneous region (planning).