using an 600 generator in an 800 service

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dannyrzk

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tulsa, OK
We are designing a city building, and I have a problem I would like to know an opinion:
We designed for a 600 amp generator feeding a 600 amp Main IN-Line panel, but later noticed there is not much room for future expansion or load. We then decided to increase the main service panel to 800 amp instead and the city accepted the cost difference to be added to the project. And here comes the problem, due to allocated fund there is no more money to increase the generator to 800 amp as happened to main service entrance panel. Since generator are smart enough to load shedding, we can control what loads are permitted and through relays turn off what exceed over 600 amp limit of the generator.

But what about the feeder from the generator to the main service entrance panel? should it be rate to the generator limits of 600 amp,or the panel 800 amp? Is this a code violation?

please see attachment.

Thank you all
 

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If the calculated load was less than 600A, how would the load on the generator exceed 600A? so why would you need load shedding at all?

i don't see how the conductors from the generator would change any based on the rating of the service panel.
 
dannyrzk said:
Bob, we are increasing the main distribution panel to 800amp, base on future load, not calculated load
Click to expand...

I am not a fan of making design decisions on what might happen down the road, and there is no NEC requirement to make such wild guesses.

As long as the wires from the generator are properly protected, I don't see a problem.

Go look at the utility transformer and see what size transformer they installed. that is what they think the real load will be. probably 300A or so.
 
petersonra said:
I am not a fan of making design decisions on what might happen down the road, and there is no NEC requirement to make such wild guesses.

As long as the wires from the generator are properly protected, I don't see a problem.

Go look at the utility transformer and see what size transformer they installed. that is what they think the real load will be. probably 300A or so.
Click to expand...

I agree. As long as the conductors from the generator are properly protected should be fine.

Think about situations where at times in computer installs a 200 amp 30 circuit panel might be fed by a 60 amp UPS or circuit where there is a request for many dedicated circuits
 
The only thing that the code cares about, besides protection, is that if there is an automatic transfer switch without any provision for load shedding the generator rating must be greater than or equal to the calculated load.
 
thank you all those are really great point, and helping to go on the right track.

How about the wire sizes from the generator to the main service?
 
Where is the overcurrent protection?

I assume the generator has a main breaker, but where is the main disconnect/OCP for the utility service? After the ATS, or is it a service entrance rated ATS?
 
steve66 said:
Where is the overcurrent protection?

I assume the generator has a main breaker, but where is the main disconnect/OCP for the utility service? After the ATS, or is it a service entrance rated ATS?
Click to expand...


you brought a good point, the OCP will be BEFORE the ATS, it won;t be a service entrance rated ATS (cost more). Thanks
 
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