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Current Flowing in a star delta motor cables

Current Flowing in a star delta motor cables

Current Flowing in a star delta motor cables

(OP)
People,
Can someone explain the mathematics behind the current that flows in one of the legs of a motor in star delta configuration.  There are six connections - one from each end of the six coil terminals.

I believe that if the motor full load current is 100%, then the current magnitude in each leg is 58% (=1/sq root of 3).

Much Thanks

RE: Current Flowing in a star delta motor cables

If you connect star then the phase voltage is 0.577 line voltage.  If you connect delta then phase voltage is line voltage.

RE: Current Flowing in a star delta motor cables

Adding to previous post:
There are three circuits in the motor.  Phase A is T1 and T4.  Phase B is T2 and T5.  Phase C is T3 and T6.  The motor you have may have different markings such as U1-U2, V1-V2, W1-W2.  Same thing.  When the motor is connected star, or wye, the voltage that is applied to the winding is 1/1.732 times phase voltage.  When the connection is changed to delta then phase voltage is line voltage.
If you have a nameplate rated 460 volt motor rated star start and delta run then the motor will be connected for 796 volts on start but will only get 460 volts applied; so it starts a little slower.  When the contactors connect it to delta then the motor attains full power. Acceleration time is dependent on the load.  Hope this helps.

RE: Current Flowing in a star delta motor cables

Yes, the current in each of six leads is 0.577 per-unit of nameplate.  Remember to apply (99)NEC310-15(b)(2)(a) ampacity-adjustment factors if the six leads are in a raceway or cable.

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