Enter Values
Formula
Single-phase A = hp × 746 ÷ (V × efficiency × PF)
Three-phase A = hp × 746 ÷ (√3 × V × efficiency × PF)
This is an engineering estimate. Use the motor nameplate and applicable electrical code tables for equipment and conductor sizing.
Example
A 10 hp, 460 V three-phase motor at 90% efficiency and 0.85 PF has an estimated full-load current of 12.24 A.
What This Estimate Represents
Horsepower is converted to mechanical watts, then divided by efficiency to estimate electrical real power. Voltage, power factor, and phase determine the corresponding running current.
Use the motor's rated voltage, full-load efficiency, and full-load power factor when those values are available.
Nameplate Current vs. Code-Table Current
The motor nameplate current can differ from both this formula estimate and electrical code table values. Different rules may use different currents for overload protection, branch-circuit conductors, short-circuit protection, and disconnect sizing.
Use the applicable code edition, manufacturer instructions, motor nameplate, and equipment listings for an installation. Starting current is much higher than calculated running current.