Help With Generator Install

[Rickhe]

Hi Mike
​

I hope all is well. I wonder if you could help me with a generator question.
​

I am installing a optional standby generator system. I am installing a 400
​

amp 277/480 volt main supplying a 400 amp automatic transfer switch. Which
​

in turn will be supplying a 400 amp distribution panel. My actual calculated
​

load will be around 150 amps. Can I install a generator capable of 200 amp
​

with a main breaker over current protection to supply my 400 amp transfer
​

switch ? Trying to interpret NEC article 702.4 B 2
​

Thank you
​

 

[GoldDigger]

Unless your ATS includes a load shedding function the generator needs to be able to handle the calculated load, but not necessarily the POCO service size.

Sent from my XT1585 using Tapatalk

 

[Rickhe]

Thanks for your the response. So your interpretation of article 702 is the generator can be sized to my calculated load of 150 amps. Not the 400 amp service I have everything sized for. So using a generator with a 200 amp main would be allowed based on calculated load.

 

[publicgood]

Hi Mike
​

I hope all is well. I wonder if you could help me with a generator question.
​

I am installing a optional standby generator system. I am installing a 400
​

amp 277/480 volt main supplying a 400 amp automatic transfer switch. Which
​

in turn will be supplying a 400 amp distribution panel. My actual calculated
​

load will be around 150 amps. Can I install a generator capable of 200 amp
​

with a main breaker over current protection to supply my 400 amp transfer
​

switch ? Trying to interpret NEC article 702.4 B 2
​

Thank you
​

Yes. The frame size of the transfer switch is often larger than the feeder serving it in order to comply with UL 1008 (KAIC rating).

702.4 B 2 is only concerned that the generator is capable of carrying the transfer load and in your case calculated says it can.