Can Residential Generator be Smaller than Service Size?

[JediMike]

I am an electrical designer in Mass, and I am seeing a lot of existing conditions at homes where, for example, a residential house has a main service of 400 amps, and the main disconnect is a service rated 400 amp ATS, but the generator is only a 200 amp generator with no generator panel. So basically it's a whole-house backup, but with only half the available amperage as the main service. I know that most residential houses do not use nearly as much amps as we have to design for, but is it a code violation to have a setup like I mentioned? I was brought on to a design/build project to review the installation where the EC is doing something similar. Where in the code does it say he can or can't? Any help would be appreciated.

 

[Electromatic]

Look at Article 702. The generator has to be capable of supplying the full load if there is an Automatic Transfer Switch or there has to be some kind of load-shedding system.

 

[Coppersmith]

To add to what @Electromatic said, a load calculation or study has to be performed to determine the actual load. If that load is less than or equal to what the generator can handle, then the situation is code compliant.