Main breaker+contactor+thermal overload for star delta starter

The main breaker should be sized ad 150% of the motor Full load current, the overload should be sized at 115% or 125% of the Full load current that depends on the service factor. You conductors can be sized at 125% of the motor full load current, and the contactors can be sized at 58% of the motor full load current for the main and delta contactors and 38% for the star contactor.

Normally I would just use contactors of the same value but some engineers use that calculation. Reason the using a smaller contactor then the motor for delta and main is because when the motor makes the change to delta the current splits in half between both contactors.


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