The current drawn by a motor during ‘starting’ is often specified on the motor nameplate specifications as locked rotor amps (LRA). This current is typically five to six times the full load amps (FLA) of the motor, and as high as ten times FLA for high efficiency motors. This inrush current lasts only until the motor shaft has reached its rated speed, so it is typically of very short duration, perhaps less than one second. To work out KVA required use start current times this by 3 (3 phases) then divide by 2, then divide by 4.2
Example: 42a x 3 = 126
126 ÷ 2 = 63
63 ÷ 4.2 = 15KVA
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