Residential standby generator ATS

E

Eliaso

New User
Location
Albuquerque NM
Occupation
Electrician
I’ve been doing quite a few Resi standby generators. Most I’ve used a service rated 200 amp ATS installed right after the utility meter. Recently a inspector questioned the size of the generator that services the ATS. It’s a 26kw with a 110 amp breaker. So I ran #3 copper from the ATS to the Gen. He’s trying to say that generator need to provide 200 amps since is feeding a 200a ATS. I’m trying to find an article that explains if this 26kw is acceptable. I’m in Albuquerque NM. Thanks for the help.
 
Seemingly we are looking at two different issues.
As to the 26kw being large enough that would be dependent on the connected load.
As to the wire size, the conductor normally should be protected no greater than it's ampacity. There is some debate as to 310.15(B)(7) being allowed in this case. Locally it is not so the #3 would be undersized based on the 110 amp breaker but a 200 amp conductor would not be necessary simply one based on the generator OCP device in this case a #2 cu
 
Aside from wrong conductor size, I think the op is saying the inspector wants a generator large enough to run the full 200 amps, which is not required if the calculated load is not. If the calculated load is larger than what the generator can provide, then load shedding must be used.
 
The code section is 702.4(B).

The issue is the AHJs definition of "Full Load". I would start by proving that the generator can handle the load if the automatic transfer is used. The AHJ might require that "Full Load" be the size of the service's main breaker.

The enhanced content (not code, but good guidance) says the generator, "must have the capacity to supply all the loads connected to it" (NEC 2020 Handbook from NFPA Link).
 
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