Motor Control Center Circuit Breakers with Current Limiters
Motor Control Center Circuit Breakers with Current Limiters
(OP)
Is it common practice to use current limiters with circuit breakers to limit short circuit current in power circuits for smaller loads fed from Motor Control Centers (MCCs)? I am finding that when sizing cables for available short-circuit currents per ICEA P-32-382-2007 that I have to upsize cables frequently for smaller loads like Motor Operated Valves (MOVs) and smaller pumps. I understand that ICEA P-32-382-2007 is generally conservative to account for faults at any point in a circuit, and this leads to the results that I am getting. Is there any additional guidance that would allow me to justify a smaller cable size for this application?






RE: Motor Control Center Circuit Breakers with Current Limiters
RE: Motor Control Center Circuit Breakers with Current Limiters
The only time I use current limiters or CL breakers in MCCs is if the Available Fault Current ahead of the MCC is greater than 65kA. My experience is that this is exceedingly rare.
"Will work for (the memory of) salami"
RE: Motor Control Center Circuit Breakers with Current Limiters
RE: Motor Control Center Circuit Breakers with Current Limiters
RE: Motor Control Center Circuit Breakers with Current Limiters
"Will work for (the memory of) salami"
RE: Motor Control Center Circuit Breakers with Current Limiters
Check if the calculation is really required by the code.
Check if you're using the correct fault current (i.e., at the correct location).
RE: Motor Control Center Circuit Breakers with Current Limiters
But current limiting is not needed to protect the cable if the maximum short circuit at the end of the wire run is within the wire's short circuit withstand for the breaker's tripping time. If the fault is in the middle of the wire run, the wire is already damaged and needs to be replaced anyway.
Also, it doesn't take very much wire length to drop the short circuit to acceptable levels. The first 10 meters of wire may be the only portion that is not protected against melting during a short circuit. Any fault beyond that is usually within the wire's capability.