Motor Current & Breaker Calculator
Estimate single-phase or three-phase motor full-load current from HP, voltage, efficiency and power factor, then calculate starting current and a preliminary standard breaker size from a user-selected protection multiplier.
Estimated full-load current
6.78 A
125% design current
8.48 A
Estimated starting current
40.7 A
Breaker calculation basis
8.48 A
Next standard breaker rating
10 A
Important: Motor breaker selection depends on the applicable code, breaker/fuse type, starter, overload relay, motor nameplate current, locked-rotor current, cable ampacity and available fault current. Use this result only as a preliminary calculation and verify the final protective-device settings with the governing standard and manufacturer data.
Motor current formulas
Single phase: I = HP × 746 / (V × η × PF). Three phase: I = HP × 746 / (√3 × VLL × η × PF). Starting current is estimated as full-load current multiplied by the entered starting-current multiple.
Why breaker size is not just 125% of current
The overload device protects the motor from sustained overcurrent while the branch short-circuit and ground-fault device must tolerate normal starting inrush and still clear faults safely. Different standards and protective-device types permit different sizing methods, so the multiplier above is deliberately user-controlled.