CT sizing
CT sizing
(OP)
What are the standards or criteria for selection of CT primary rating for a motor feeder? If motor full load current is 40A, can I use a 40/1 CT OR the CT has to be rated higher say 50/1 or 60/1?? Let me know the guidelines please. If 40/1 CT cannot or should not be used, what are the disadvantages?






RE: CT sizing
Regards
Marmite
RE: CT sizing
Usually, motor are protected by contactor and by fuse, so the relay doesn't have to work under large short-circuit current. If it does, more precaution should be taken for saturation of CT.
If you choose a CT with the same nominal current as the motor, the ct will heat more. You should check the ct datasheet to validate it's ok.