Adding Generator to Existing Home Feeder Size

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Npstewart

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Hello everyone. We are adding a generator to a existing home. The existing service is 600A which is over sized because the original engineer used the optional calculation to size the service but took the pool panel at 100% and didnt bother taking advantage of the 40% reduction at the service level after the first 10 kVA.

We are now adding a generator to the house. Our demand load is 310 Amps. Rather then typing my whole question, I just drew a diagram. Please see attached. My thinking is that the feeder will need to be rated for 600A, not 400A but I would like some input. Thanks in advance.
 

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GoldDigger

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Npstewart said:
Hello everyone. We are adding a generator to a existing home. The existing service is 600A which is over sized because the original engineer used the optional calculation to size the service but took the pool panel at 100% and didnt bother taking advantage of the 40% reduction at the service level after the first 10 kVA.

We are now adding a generator to the house. Our demand load is 310 Amps. Rather then typing my whole question, I just drew a diagram. Please see attached. My thinking is that the feeder will need to be rated for 600A, not 400A but I would like some input. Thanks in advance.
Click to expand...
Unless you change the overcurrent protection at some point to 400A, I think both feeder sections need to be 600A rated. And since there is no disconnect on the meter side of the ATS, the ATS will need to be service rated at 600A also.
The generator itself does not have to be sized to the service, but when you have an automatic TS it has to be sized to the calculated load or else needs to include load shedding relays downstream.
Or you can downsize everything to 400A. :)
 
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Volta

Senior Member
Location
Columbus, Ohio
I agree. Assuming the ATS has an 600 amp OCPD, the load-side feeder would have to be 600 amps, unless the MPD has a main that can be replaced with a 400 amp unit under a tap rule. Probably cheaper to run the larger feeder.
 
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Npstewart

Senior Member
I think I am going to replace the 600A ATS with a 400A ATS which I have on my real riser as service entrance rated. The 600A main breaker in the MDP isnt actually required anymore and it doesent serve any purpose.

Thanks Guys!
 
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