How do I calculate Three-Phase Motor Current & Protection?

To calculate Three-Phase Motor Current & Protection: Enter Shaft power Pa, Line voltage (L-L), Motor efficiency η and other values. Click Calculate. INDUGRID computes the result instantly using the formula: IN = Pa / (η × √3 × U × cos φ) [A] | I_start = IN × (IA/IN). No registration required.

What units does the Three-Phase Motor Current & Protection calculator use?

The Three-Phase Motor Current & Protection calculator uses the following units: kW, V, %. SI units are used by default.

Electrical Engineering

Three-Phase Motor Current & Protection

Calculate nominal current, start-up current and thermal protection settings for three-phase induction motors.

Units:

in LinkedIn

💡At direct-on-line start, an induction motor draws 5–8× nominal current for 1–10 seconds. Always use gL/gG (slow-blow) fuses for motor protection. Overload relay must be set to nominal current IN. Star-delta reduces starting current to 1/3.

IN = Pa / (η × √3 × U × cos φ) [A] | I_start = IN × (IA/IN)

Input

Shaft power Pa iNominal shaft power from the motor nameplate in kW. This is the mechanical output power, NOT the electrical input.

Line voltage (L-L) iLine-to-line supply voltage in Volts.

Motor efficiency η iMotor efficiency in %. IE2: 85–92%, IE3: 87–95%, IE4: 90–97%.

Power factor cos φ iMotor power factor from nameplate. Typically 0.78–0.92.

IA/IN ratio iStarting current as multiple of nominal current. Squirrel-cage motors: typically 5–8.

Result

Electrical input power [kW] —

Nominal current IN [A] —

Starting current (DOL) [A] —

Overload relay setting (DOL) [A] —

Overload relay setting (star-delta) [A] —

Minimum fuse rating (gL, DOL) [A] —