Article 700 Selectivity requirement

[mshields]

Does this controversial requirement (700.27) to have full selectivity (including in the instantaneous range) apply to the normal side of the Article 700 ATS?

Mike

 

[ryan_618]

Reading the scope of 700.1, Article 700 applies all the way to the equipment. With that said, yes, it applies to the normal side as well.
...I hope you have stock in Bussmann fuse...

 

[mshields]

I don't see that

I don't see that

Here is 700.1

"The provisions of this article apply to the electrical safety of the installation, operation, and maintenance of emergency systems consisting of circuits and equipment intended to supply, distribute, and control electricity for illumination, power, or both, to required facilities when the normal electrical supply or system is interrupted.

Emergency systems are those systems legally required and classed as emergency by municipal, state, federal, or other codes, or by any governmental agency having jurisdiction. These systems are intended to automatically supply illumination, power, or both, to designated areas and equipment in the event of failure of the normal supply or in the event of accident to elements of a system intended to supply, distribute, and control power and illumination essential for safety to human life."

Paragragh 1 would indicate to me that we are not talking about the normal side of the ATS. Paragragh 2 seems to further support this. i.e. the statement "These systems are intended to automatically supply illumination, power or both" seem to me to make clear that we are not talking about the normal side of the ATS, i.e. the side that would have to be lost in order for the "emergency system" to kick in.

Mike

 

[ryan_618]

Mike: I apologize, I misread what you were asking. I agree with you, the normal side of the transfer switch doesn't need to meet this requirement. When I read your question initially, somehow I read into it that you were talking about the load side of the ATS, not the line side (service).

 

[mshields]

No problem

No problem

Thanks for the input as always!!!

 

[dbpe]

I'm afraid I have to partially disagree with Ryan on this. Although the distribution on the line side of the transfer switch is not part of the clasification described by Article 700, the requirement for selective coordination from an Article 700 load (and 701 and 508) absolutely extends into the distribution system on the line side of the ATS. The code text states that the emergency system overcurrent devices must selectively coordinate with "..all supply side overcurrent devices". Although inconvenient, how can it be interpreted that the selective coordination of the supply side devices feeding emergency circuits stops at the ATS? IMO "all supply side devices" means exactly that - every upstream device including the generator output breaker on the emergency source side (assuming it feeds more than the one branch device) and the service entrance overcurrent device on the normal side.

 

[don_resqcapt19]

The OCPDS on the normal side of the ATS are on the "supply side" of the emergency system OCPDs and must be selectively coordinated.

700.27 Coordination
Emergency system(s) overcurrent devices shall be selectively coordinated with all supply side overcurrent protective devices.

Don