thermal protection for motor (49) 1

[center104]

for motor protection circuit, we have two scheme. Scheme A is fuse/CB + contactor + thermal over load, Scheme B is fuse/CB + contactor + relay. I find Scheme B is popular right now ( I am not sure I am right). Please give me your suggestions based on your experience.

thanks

 

[dpc]

A motor protection relay can provide thermal overload protection as good as, or better than a bi-metallic or solid-state motor overload relay, and allows for greater flexibility in adjustment of the thermal replica for the motor. In addition, the relay can provide many other protective and metering functions. The relay will generally be much more expensive and is normally reserved for larger motors, especially medium-voltage.

Thermal overload protection of some type is required.

 

[sslobodan]

But can be found for smaller motors also. And i don't think that price is so different because it is more like standard now

 

[electricpete]

At our plant for smaller motors powered from MCC's we use scheme A (molded case circuit breaker, contactor, and thermal overload heater associated with the contactor)

For larger motors powered from load centers we use a metal frame breaker and a relay... no contactor.

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