3-Phase Motor FLA & Branch Circuit Calculator
Determine 3-phase AC motor full load current (FLA), 125% minimum wire sizing ampacity, and maximum overcurrent protection per NEC Article 430.
Motor Rating & Voltage
Branch Circuit Overcurrent Device
Motor Current & Sizing Results
Frequently Asked Questions
Why does the NEC require Table 430.250 values instead of motor nameplate FLA?
Per NEC 430.6(A)(1), conductors, switches, and branch-circuit overcurrent protection must be sized using NEC table values rather than actual motor nameplate amps. This guarantees that if a motor is replaced in the future with a lower-efficiency motor of the same horsepower, the wiring will not be undersized.
Why can a motor circuit breaker be sized up to 250% of FLA?
Standard 3-phase induction motors draw 600% to 800% of their full load current during across-the-line starting. To prevent nuisance tripping during rotor acceleration while still providing short-circuit protection, NEC 430.52 allows inverse-time breakers to be sized up to 250% of FLA (separate thermal overload relays protect against motor running overloads).
What is the 125% branch circuit conductor multiplier in NEC 430.22?
Conductors supplying a single continuous-duty motor must have an allowable ampacity of not less than 125% of the motor full-load current rating to accommodate sustained continuous heating under full load.