Relationship between 700 and 517

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charlie b

charlie b

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For this health care project, NEC 2008 applies. Article 700.9(B)(5)(b)'s exception allows a breaker at the backup source (diesel generator), provided that it selectively coordinates with downstream devices. Article 517 uses the term "emergency" for both the life safety and critical branches. I infer that that would bring article 700 into play. So if I have a generator that has its own breaker and that supplies life safety, critical, and equipment branches from a common board, and if the common board has separate breakers serving separate transfer switches, I believe that the breaker at the source must selectively coordinate with each of the three breakers that feed the three ATS's. Comments? Agree/disagree?
 
I was thinking essential electrical system was the term that describes the type of branches.
I also believe that critical circuits should not share any type of raceway or enclosure other than with critical circuits.
If the required back up generator is 150 kw or less then it can feed the EES. 150 or more would need 2 ATS s.
So u have a distribution panel that has critical , equipment and life safety branches as well as feeds 3 ATS s , then the generator is taped 3x to each ATS ,and theres no 480v circuits for VAV s or med gas etc?

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517.30 says that the break point is
"with a maximum demand on the essential electrical system of 150 kVA". The generator could be larger.
 
I found my answer in 517.26. Thanks for the assistance.

I am doing a peer review of a project designed by one of our other offices. They selected a 750 KVA generator. I am going to include, as one of my comments, that they are going to have to show selective coordination between the generator breaker and the three breakers that serve the three ATS's.
 
517.26 2014 has been revised to require Article 700 compliance only on the life safety branch.

517.26 Application of Other Articles. The life safety branch
of the essential electrical system shall meet the requirements
of Article 700, except as amended by Article 517.
 
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