Jump to content

Overcurrent relay circuit position and variable settings in star and delta connected induction motor.

Recommended Posts

Good evening, 

I have a few questions requiring your expertise:


For a motor with a nameplate FLC of 44A:

The overload relay trip setting should be set to 44A when connected in Delta and set to 44/(root 3)=25.4A when connected in Star. 

Is this statement correct?


Does the position of where the overcurrent relay is connected in the power circuit have any effect what the trip setting is set to?

For example, if the OCR is connected in series AFTER the main contactor, would it have the same trip setting is it was connected before the contactor? In this case, my understanding is the OCR is monitoring the line current as it is connected to the supply line in series with the contactor and the motor which is why the OCR is different as per my 1st statement. 

There are cases where there is no individua  OCR in some motor starter circuits  but instead a motor circuit breaker GV-2 with both thermal overload and short circuit protection, so in essence, it acts as a combined circuit breaker and OCR. 

Would the GV2 have a different thermal overload setting than an individual OCR because it is connected before the contactor?

Thanks very much,


Link to comment
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
  • Create New...