Emergency Generator

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rich000

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Here is the situation. The customer has an emergency generator with plenty of capacity to add a UPS for backup to the computer room.

The generator backs up an existing emergency panel (via an ATS) that supplies lighting and elevators.

I cannot find the code (700?) that would prevent them from putting the UPS on the existing E-panel.

I thought that if there was one generator and they were using it to supply emergency circuits for life safety (lighting, elevators, exit signs), then they would have to add a second ATS off the generator and power non-critical loads that way.

Article 700.5 (B) I thought might apply, but this is a "shall be" article.

Any help please.

Thank you.
 
Re: Emergency Generator

700.6 (D) and 700.9(B).

I think you only need separate transfer switches. Others think you need separate feeders clear back to the generator, including not sharing a "main" breaker on the generator.

This only applies for "legally required systems". It doesn't apply if only article 701 applies (which I think is unlikely).

Steve
 
Re: Emergency Generator

700.5(B) does apply too. How would you get automatic selective load shedding without separate transfer switches? I guess it would be possible, but hard to to.

Steve
 
Re: Emergency Generator

But if the generator is adequately sized, why the extra transfer switch? 700.5(B) looks more like a recommendation. It does not specify that SEPERATE transfer switches are needed, just AS NEEDED.
 
Re: Emergency Generator

According to chapter 27 of the IBC, egress lighting must be emergancy(700), whereas elevators must be standby(701). In my opinion, this would require 2 transfer switches, as per 700.6(D).
 
Re: Emergency Generator

OK. Thanks all. I wanted a good clarification and the code reference. I think this will work. I just was not sure this was the right way to explain the code issue.
 
Re: Emergency Generator

Can you have an Emergency/Stand-By generator by adding a second ATS ??
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I think so. Some people here have expressed the opinion that the generator would have to have separate "main" breakers to keep the wiring "totally independent". But if that were the case, the generator windings would still be common, so you still have some interconnection.

I think you have to keep the systems separate at least to the transfer switch, and maybe even back to the essential panelboard.

Steve
 
Re: Emergency Generator

I just finished a project involving this issue and I had a 600A main (optional stand-by power) and a 100A main (emergency power) both located at the gen-set, 2 separate xfer switches, and 2 separate panels, 1 for critical process and 1 for emergency and egress lighting. This is what is required in Cincinnati.
 
Re: Emergency Generator

The computers would need a 3rd transfer switch because they are an optional standby load.

The requirement for load shedding applies to situations where the generator could be overloaded. If your generator is big enough and the sum of main breakers for emergency, legally required standby, and optional standby loads do not exceed the rating of the generator then you only need to add load shedding if the system is modified at a later date.
 
Re: Emergency Generator

I thought you could have optional and legally required on the same transfer switch, just not emergancy. I see nothing in 701.7 that mirrors the requirement of 700.6(D).
 
Re: Emergency Generator

I'll second that Ryan. One transfer switch for Article 700 emergency systems, one for everything else.

I'll also agree to no load shedding if the generator is large enough to run everything.

Steve
 
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