Separate ATS for Article 700 loads... OK to feed from load side of service ATS?

jtrezon

Member
Interested in a more learned opinion on this topic.... distribution designs where an entire service is backed up via a standby generator and SE rated ATS.

I understand a separate ATS is always required for Article 700 loads (Emergency lighting), but I have a question on where the NORMAL supply to the "Article 700 - EM Lighting" ATS typically connected? I have see (and installed) instances where it was connected somewhere on the load side of the main SE ATS, but tend to think that would defeat the purpose of switching these loads separately....the downstream ATS would react to the ATS upstream.

Would a better option be to have a separate service disconnect tapped ahead of the main SE ATS?.. typical to just have two mains on the building in this instance? I would love to hear some more experienced opinions on how this is typically designed and the reasoning / advantages.

FYI....the standby generator would have two separate load breakers....one for each ATS.

Much appreciated in advance
 

texie

Senior Member
Location
Fort Collins, Colorado
Occupation
Electrician, Contractor, Inspector
Interested in a more learned opinion on this topic.... distribution designs where an entire service is backed up via a standby generator and SE rated ATS.

I understand a separate ATS is always required for Article 700 loads (Emergency lighting), but I have a question on where the NORMAL supply to the "Article 700 - EM Lighting" ATS typically connected? I have see (and installed) instances where it was connected somewhere on the load side of the main SE ATS, but tend to think that would defeat the purpose of switching these loads separately....the downstream ATS would react to the ATS upstream.

Would a better option be to have a separate service disconnect tapped ahead of the main SE ATS?.. typical to just have two mains on the building in this instance? I would love to hear some more experienced opinions on how this is typically designed and the reasoning / advantages.

FYI....the standby generator would have two separate load breakers....one for each ATS.

Much appreciated in advance
Well, If I came across a setup that you describe in your 2nd paragraph, I'd say it was done by somebody that does not understand good design practice. I would work and even be compliant but a very poor design choice.
I would also question the use of SE rated switches for most applications for various reasons.
Most installs I've done where the entire service has optional standby (Art. 702), and has a requirement for Art 700 loads as well, would have a service main for the normal load feeding an ATS and another service main feeding the art. 700 ATS for the emergency load.
For something like, say, a small office building that has minimal emergency lighting load and the owner wants to spend the money for an entire service optional standby, sometimes it is advantageous to use battery emergency lights. That way you get the benefit of backup power with normal lights on during a power failure and still are code compliant without an extra ATS and a completely separate emergency wiring system.
 

jtrezon

Member
Thank you for the comments...
I agree with the separate service disconnect.

Owner is furnishing generator and ATS equipment so the contractor in me will overlook the SE switches. I also typically find it a cost advantage to find a way not to use SE rated equipment.... Also helps with lockout/tag out

I also agree with your comment about using batteries in smaller buildings... in this particular case, the facility is a large warehouse and that many batteries would be more of a maintenance headache.
 
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