I am reviewing a set of drawings where a 300-amp main circuit breaker panel is fed from a 250-amp circuit breaker at the swbd upstream of the panel. The designer claims that in this instance the 300-amp main circuit breaker would serve as a disconnect only since the 250-amp circuit breaker would trip in an overload situation. I know this would be acceptable for a main lugs only panel, but it does not seem intuitive for a main circuit breaker panel. The panel is existing, which is why it is a question. Does this sound correct and NEC compliant? I have my doubts.
Feeder overcurrent protection smaller than panel MCB
- Thread starter cdw238
- Start date
- Status
- Location
- Connecticut
- Occupation
- Engineer
Sounds NEC compliant to me...can't think of any section that it would violate.
texie
Senior Member
- Location
- Fort Collins, Colorado
- Occupation
- Electrician, Contractor, Inspector
In general it is not a violation and I see this from time to time for various reasons. The only exception would be if this is an environment where selective coordination is required.
- Location
- Connecticut
- Occupation
- Engineer
I don't see where coordination would be an issue either...It shouldn't matter which breaker opens first...see, for instance, 700.27 Exception.
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