Emergency Generator feeding two buildings

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ka4koe

Member
I have a design quandry. There is an existing generator / ATS feeding an existing building. The building has a dedicated service drop from the power utility. The genset has a lot of spare capacity. A new building with a separate service lateral also needs to be on emergency power. The new building will have its own ATS. The configuration will be such that each ATS will be interlocked and operate simultaneously.

Is it permissable to run a lateral from the existing genset to the new ATS?

This is an oddball situation and I want to avoid any gotchas.

Thanks.

Philip Neidlinger
KA4KOE
 

petersonra

Senior Member
Location
Northern illinois
Occupation
engineer
I have a design quandry. There is an existing generator / ATS feeding an existing building. The building has a dedicated service drop from the power utility. The genset has a lot of spare capacity. A new building with a separate service lateral also needs to be on emergency power. The new building will have its own ATS. The configuration will be such that each ATS will be interlocked and operate simultaneously.

Is it permissable to run a lateral from the existing genset to the new ATS?

This is an oddball situation and I want to avoid any gotchas.

Thanks.

Philip Neidlinger
KA4KOE
Is there any rule that says each building that requires an emergency power source has to have its own generator? The hospitals around here would be in trouble if that was the case. I think they all have a single large emergency generator for the entire complex.
 

malachi constant

Senior Member
Location
Minneapolis
The configuration will be such that each ATS will be interlocked and operate simultaneously.

I don't get that. You mean that if power to building A fails, the generator fires up, and the transfer switch goes to EM power.... that the building B transfer switch will also flip to EM power, even if power hasn't failed in building B?

Does the generator have a spare output breaker? Can one be added? I assume this would be a prerequisite for being able to use the existing generator.

Otherwise, I agree with peterson's response - one generator serves multiple buildings all the time. I haven't done enough of them to say what the "gotcha" issues are, but generally speaking it's common.
 

steve66

Senior Member
Location
Illinois
Occupation
Engineer
I would suggest you consider the neutral-ground bonding locations. I think you will find you should provide 4 pole transfer switches.

I don't see any need to interlock the two ATS's. Usually the ATS generator starting contacts are just paralleled for two ATS's.

Codewise, I believe that each building should have a generator disconnenct at the building. Not sure if these need to be located near the main utility disconnect for each building. But I think each disconnect should be labeled "Service Main 1 of 1" and "Service Main 2 of 2".
 
I would speak to an electrical engineer at the budgeting stage whether or not the existing generator should be configured as "seperately derived". This comes to mind when using 4 Pole ATS. Additionally, you could discuss installing new Panel EMDP with one circuit breaker for each ATS and/or Building. The AHJ may want signage for physical location of generator, and remote shutdown capability. Also, by adding load of the new building your fuel consumption will also increase. Should review if run time is acceptable when generator is powering both buildings based on current max fuel capacity.

Just my 2 cents.

Good luck with project!
 

ceb58

Senior Member
Location
Raeford, NC
I think the question that needs answering is. Is this a real emergency generator or is it an optional stand by system.
The reason being is people will call a generator an "emergency generator" when in fact it is by definition a stand by system. And there are different code requirements.
 
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