According to the 2005 NEC coordination of OC devices is required for Emergency Systems per 700.27. This would rule out the use of circuit breakers in these systems since you can't coordinate the instantaneous portion. It looks like fuses (or electronic CB's) are the only choice. Please provide your thoughts and comments.
overload coodination
- Thread starter bsh
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barbeer
Senior Member
- Location
- Pinellas County, FL
I don't understand why you think you can not use breakers? The short circuit ratings must all be in coordination.
davidr43229
Senior Member
- Location
- Columbus, Oh
You can use both Circuit breakers and fuses in a selctively coordinated system. The instantaneous region pertains to the shortcircuit region, where the problem lies. Some circuit breaker manufactures now publish tables for their breakers to achieve this selective coordination. You are however right they are electronic, when the settings are also listed. You can not achieve this with standard molded case circuit breakers.
Just my $.03, adjusted for inflation.
- Location
- Wisconsin
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- PE (Retired) - Power Systems
davidr43229 said:
It is possible to have thermal-magnetic breakers coordinated with upstream thermal magnetic breakers. It does absolutely depend on the available fault current at the downstream location. I know that Square D has tested and published the results of their LA-MC (mission critical) breaker with normal branch breakers, but, electronic breakers usually must be in the system eventually.
Barbeer - short circuit current ratings have absolutely nothing to do with selective coordination.
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