Series rating and selective coordination

[peter d]

Please excuse this basic question but I do mostly residential/small commercial work. This is not a test question.

So, can anyone give a "beginner's guide" to "series ratings" and "selective coordination?"

Where is this critical, and is it mandated by the NEC?

Thank you in advance.

 

[ryan_618]

Re: Series rating and selective coordination

Selective coordination is required for elevators under the 2002, and it will be required for emergancy and legally required standby systems in the 2005. Selective coordination can not be provided with series ratings.

I think I'll pipe down now and let one of the engineer's deal with it from here

 

[rbalex]

Re: Series rating and selective coordination

"Selective Coordination" simply means the overcurrent protective device (OCPD) closest to whatever is causing the overcurrent trips before any other device. In that since, overcurrent could be overload, short circuit, or ground fault.(O/L, SC, GF)

"Series Rating" is only relevant to SC/GF. It means the ..."(OCPD) closest to whatever is causing the overcurrent..." is not capable by itself to clear the fault(SC or GF)current available in the part of the circuit it is protecting and needs the assistance of an upstream device. For now, this is a tested combination of OCPDs. Beginning in 2005, in theory at least, an engineer could select a current limiting device to protect a downstream OCPD. In either case, the result is both devices would clear in most cases and they cannot be "selectively coordinated."

 

[rbalex]

Re: Series rating and selective coordination

I should have said "clears;" trips implies a circuit breaker.

[ November 15, 2004, 06:21 PM: Message edited by: rbalex ]