Does a motor overload relay open when NOT using the N/C aux in line with the contactor coil

[emiller233]

Does a motor overload relay still protect the circuit at all when NOT using the aux in front of the contactor coil (customer requested).
They're trying to tell me that it does...?

 

[Jraef]

A standard "traditional" OL relay, no. The OL relay is just a current sensing device that only acts on the aux contacts, so it's up to you to use those aux contacts appropriately.

But some people are now using what are called "Motor Protection Circuit Breakers" in lieu of traditional Overload Relays. An MPCB has its own set of contacts that would open (think Manual Motor Starter), then you would also use an aux contact to drop out the contactor. The MPCB also then provides you with a way to disconnect the motor manually. The thing it can't do however (compared to a traditional OL relay) is be capable of setting to automatically reset itself when it cools down. You have to manually re-close the contacts.