Sharing Electrical service between 2 existing buildings

[micpat]

I am working on a UPS project. The ups is being fed by a 480 volt substation in building A and will be the source of critical power in building B. Both buildings have multiple substations fed by 2 ea. 12.4kv feeders.(Double ended subs) The buildings are joined by egress bridges and common hall ways, essentially 2 separate buildings. Grounding of the 2 buildings has been addressed, My question is a code concern about the 480 volt substation in building A feeding the critical power in building B. I cannot find any specific code section that would address this, yet I am concerned about the gray area of the building attachment: bridge and hallway as claim that the buildings are treated as one building.
Can anyone help me with my code/safety concerns of this design?
Thank you,
Michael

 

[dpc]

If you are in the US, a basic NEC rule is that you cannot serve one building from another or through another building. There are some exceptions to this for campus type installations, etc.

For your installation, I'd strongly recommend discussing this with the local electrical inspector and working it out ahead of time.

It can probably be handled by appropriate signage, location of disconnecting means and interlocking.

 

[SteveWag]

Feeding an outlying building is not prohibited by the NEC. The feed to the “second” building should be treated as a service with one difference, the neutral and grounding conductors will be individual conductors, not a single conductor as in a utility service. The grounding conductor may (should) be connected to a local ground in the second building as well as any structural steel, piping etc. These connections will be secondary or additional grounds; the grounding conductor in the second building must be continuous back to the utility service and/or separately derived service in the first building.
Steve Wagner

 

[micpat]

I apologize for any misconception about the installation, the UPS is in building A next to the substation, it will be feeding a transformer in building B the feeder is a Delta connection to the transformer. The transformer is a 480V Delta to 208V/120V Y
The distance of the feeder is 400 feet, 100 ft. in building A and the rest in building B. There is an OCPD upstream at the UPS and a disconnect on the primary of the transformer.
The buildings have been bonded together, but I was concerned about the substation Xformer in building A and the possibility of a potential difference in building B due to the different HV feeders. This issue of mixing 2 individually / separately derived systems is my concern, however if someone else has additional information with respect to this design please chime in!

 

[EEJaime]

If your concern as stated in your OP is regarding the code restriction to a single service, you are ok as your installation is one of the specific exceptions noted in 230-2(a) as allowing multiple services.

If on the other hand your concern as stated in your last post is in regards to potential differences, (on the grounded conductor?), I still feel you are ok. Since the second feed is to the critical loads in building B, I do not see where you would have both power systems present at any single piece of equipment.

In keeping with what DPC noted, it would still be a good idea and your AHJ would probably require that all circuits fed from the critical power system be properly identified including the location of the Main and downstream overcurrent protective devices and disconnects so that someone servicing these circuits does not assume that power has been disconnected if the building B main is opened.