Motor Circuit Protector Multiple Feeder

[W@ttson]

Hello,

If I had a MCCB (Molded Case Circuit Breaker) and needed to size it for multiple motors I wouldn't have an issue. Get the OCPD of the largest motor and then add the FLA of the second. Each motor has its own Overloads. Done.

Now how about for an MCP? Do I still get the circuit breaker size for the largest motor and then add the FLA (i.e. 800% of the largest motor FLA + FLA of second)? MCPs can only come as combination controller and CB with overload. How do I accomplish having separate overloads for each motor to be NEC compliant?

The reasoning behind this is that there is an existing MCP for one existing motor and I want to put 2 motors in its place (each half as large as the existing). I don't want to reconfigure the MCC bucket into an MCCB. I just want to make adjustments on the MCP.

 

[W@ttson]

Hello,

If I had a MCCB (Molded Case Circuit Breaker) and needed to size it for multiple motors I wouldn't have an issue. Get the OCPD of the largest motor and then add the FLA of the second. Each motor has its own Overloads. Done.

Now how about for an MCP? Do I still get the circuit breaker size for the largest motor and then add the FLA (i.e. 800% of the largest motor FLA + FLA of second)? MCPs can only come as combination controller and CB with overload. How do I accomplish having separate overloads for each motor to be NEC compliant?

The reasoning behind this is that there is an existing MCP for one existing motor and I want to put 2 motors in its place (each half as large as the existing). I don't want to reconfigure the MCC bucket into an MCCB. I just want to make adjustments on the MCP.

Well this is an open and shut case. It helps to once in a while go back to the NEC articles that you end up using all the time because you start taking them for granted.

Second sentence of 430.53: "The branch-circuit protective device shall be fuses or inverse time circuit breakers."

My question basically explains why that must be so.

 

[Jraef]

MCPs cannot be used for ANYTHING other than as part of a listed factory assembled combination motor starter, you cannot use them on your own no matter what. So there is no point in contemplating this application.

 

[iceworm]

spraymax, Jraef -
You both, of course, are correct.

However, let us not forget the portion of 'da brudder-hood' that would use Mag-only CBs for other applications

forums.mikeholt.com/showthread.php?t=197931