Motor Current

Supply current and starting currents of a three- or single-phase induction motor from its nameplate data — the first step in sizing breakers, fuses and cables.

ElectricalMotorStarting

Rated current I_N14.5A

Active power drawn: 8.43 kW
Apparent power S: 10.03 kVA
Reactive power Q: 5.44 kVAr
Direct-on-line starting current: 101 A
Star-delta starting current (≈ 1/3): 34 A
Rated torque T_N: 49.1 N·m

METHOD

How it is calculated

I_N = P / (√3 · U · cos φ · η)      (three-phase)
S = P / (η · cos φ)      Q = S · sin φ
I_start ≈ (5…8) · I_N   ·   star-delta ≈ 1/3

ASSUMPTIONS & NOTES

P is the nameplate shaft power.
Soft starters and drives can limit starting current to about 2–4·I_N.

Results are for preliminary design and checking; base the final design on the governing standard and safety factors.

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