Does a remote motor starter overload protect line side conductors?

[abdalton]

Imagine we have an MCC that feeds a remote motor starter that is 100 ft away from the MCC. Does the overload at the remote starter provide sufficient overload protection for the cable from the MCC to the remote starter?

Is it possible to somehow have an overload condition caused by the cable itself or a loose termination that the overload at the remote starter would never see?

 

[augie47]

IMO, if the MCC had only SCGF protection, it is possible but quite rare.

 

[petersonra]

Imagine we have an MCC that feeds a remote motor starter that is 100 ft away from the MCC. Does the overload at the remote starter provide sufficient overload protection for the cable from the MCC to the remote starter?

Is it possible to somehow have an overload condition caused by the cable itself or a loose termination that the overload at the remote starter would never see?

It does not matter where the overload is physically located in the conductors going to the motor. It is there to open the load to the motor if the current exceeds the ol setpoint.

The wiring has to also be protected from short circuits but that is a separate function presumably located at the mcc

I suppose you could come up with some crazy condition where you could create an overload upstream of the overload device but that would be pretty rare and the code does not require you to protect against such a rare occurrence.

I've actually had overloads fail and not open a circuit when a motor was overloaded. Would you have to have two overloads in series to prevent such a thing? There are all kinds of crazy things that might happen but the code does not require you to protect against this particular kind of craziness.

 

[abdalton]

I agree that an overload condition caused by something other than the motor itself is unlikely. I was having a debate with a coworker who thought this would be something to be concerned about. Good to hear it's not just me who thinks this is not a problem. Thanks!

 

[kwired]

I agree that an overload condition caused by something other than the motor itself is unlikely. I was having a debate with a coworker who thought this would be something to be concerned about. Good to hear it's not just me who thinks this is not a problem. Thanks!

Unless you supplied some other load ahead of the motor overload, but if you have a situation where you are even allowed to do so, you may need to reevaluate what size the conductors should be.

Motor overloads inherently protect the motor circuit conductors from overload, the branch circuit OCPD however is usually only for short circuits and ground fault protection as it usually needs higher setting than it would for a general purpose circuit supplying same amount of load to allow for motor starting current.

 

[winnie]

To overload conductors without it being a hard short circuit, you need some sort of impedance to limit the current.

In any sort of reasonable situation, if you have a resistive fault that causes overload current without tripping the breaker, you would get lots of heat and the fault would quickly develop into a solid short.