Emergency power panel in a seperate building

[Paul Allen]

Hi all, I was approached by a customer about bidding a project to install a emergency power feeder to an office to feed computers, lights and associated equipment from generator power. Problem with the job is that the emergency power is fed off of an emergency generator in a separate building nearby. Both buildings are separate,with separate services, but under the same management.
My statement of work says to disconnect a 100 amp panel feeder off of the existing MDP and connect it to a junction box and feed it from the emergency panel located in a building next door. Provide new conduit wire, breaker etc. etc.
First question that comes to mind is a service disconnect for the emergency panel in the separate building.
I believe we will need to provide one at a minimum, grouped with the normal main disconnect for this building.

My main question though, and the point of my indecision is this. Is there any problems with installing a separate service for this panel with its own disconnect,labeled as being fed from another building on site. Or would good engineering practice require us to install a transfer switch and leave the loads on the existing building service, with emergency power available from the other building EDP to feed the switch in the event of a building outage. I have researched this and don't see any real NEC problems with doing it either way, but my gut is telling me the transfer switch install is the right way to do it. I am really not trying to over engineer the project, but I don't think the way the customer is requesting it to be done is the correct way to do it.
I would like to hear others opinions about how they would approach this

Thank in advance for your help!
Paul Allen

 

[iwire]

My first couple of points may seem petty but are important if we are to answer the questions.

First off you are referring to this as an emergency generator yet the loads being supplied from it indicate is an optional standby generator. We must determine which kind of generator it is as that determines if article 700 applies or if article 702 applies. The rules for each are different with article 700 emergency being much more restrictive.

Next issue is you keep calling it a service, it is not, it is a feeder. Services only come from a utility. See the definition of service in article 100. Because this will be a feeder supplying one building from another part II of article 225 applies. It is in that section you will find the requirements for the disconnecting means at the second building.

 

[luckylerado]

If there is capacity enough on building A to support building B, I would ditch the second service and replace the old meter at Bldg B with a new disconnect.

If building A and B are indeed separate services and fed from separate utility transformers, I would avoid putting them into the same ATS.

 

[Paul Allen]

Thanks guys for the inputs. To clarify my previous post, This would be considered a "optional standby" generator and not an "emergency" system, as there are no life safety type circuits being powered by this proposed panel. And yes, I misspoke, it is not a service by definition, because it is not fed by utility conductors, it is a feeder.
Thank you for the suggestion to apply article 225. This clarifies the requirements for the project. I was looking in articles 700 and 702, but had not reviewed article 225 yet before I posted. The requirements for this project are indeed there. I should have went there first. Thanks for the correction and direction.
I also agree about the two circuits in the ATS. That was another quandary of mine. I was trying to keep this panel feeder on the same building meter and just feed the emergency power from the separate source, but I think as I stated earlier I am over thinking this project. I should remove the panel from building A all together and connect it to building B(Emergency source supply), and provide a separate disconnect on switch on building A to allow it to be disconnected if needed to comply with 225.31.

Thanks for the help on this.

Paul

 

[iwire]

If building A and B are indeed separate services and fed from separate utility transformers, I would avoid putting them into the same ATS.

Why?

What would be the need of that?

 

[luckylerado]

What would be the need of that?

I could see someone installing an ATS on the building that currently does not have EM power (B) and using a feeder from building A as the EM source. So there could be some crazy phase angles and fault current potentials in the ATS, even though presumably limited by an OCP device and presumably an open transition.

This becomes critically important at higher voltages and with parallel gensets and or utility feeds.

 

[iwire]

I could see someone installing an ATS on the building that currently does not have EM power (B) and using a feeder from building A as the EM source. So there could be some crazy phase angles and fault current potentials in the ATS, even though presumably limited by an OCP device and presumably an open transition.

This becomes critically important at higher voltages and with parallel gensets and or utility feeds.

The addition of a seperate ATS has no impact on those issues.

The two services would not be connected together at anytime unless someone violates the code.

It is not unusual for one genertor to supply multiple buildings.

It is not unusual for one building to have two services, say 240 delta and 120/240 single phase from seperate transformers.