Serving a building with 480/277V & 208/120V

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faresos

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We have an existing facility (small air port) that is served from 2000A, 208/120V service. The user wants to expand the building. There are many large loads to be added and served from 480V system such as Jet Bridge (total of 175KVA), 5 Ground Power units and HVAC equipment. Can we provide a 480v service for the expansion part? In another word, this building will be served from 208/120V (existing service) and new 480/277V service. Thanks,
 
You can. See 230.2(D) for the allowance & 230.2(E) for some requirments
 
would it really be an additional service?

does the airport own the existing 208V transformer?

if all you are doing is setting another transformer off the same service you won't have another service, but another feeder.
 
petersonra said:
would it really be an additional service?

does the airport own the existing 208V transformer?

if all you are doing is setting another transformer off the same service you won't have another service, but another feeder.
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The transformer is owned by the utility.

Why you don't think this is not another service? We will be setting a second utility transformer to feed the expansion part of the airport. Which most likely we will have another meter (total of two, one for each transformer).


When you said "the same service" did you mean the primary feed for the transformers?
 
faresos said:
The transformer is owned by the utility.

Why you don't think this is not another service? We will be setting a second utility transformer to feed the expansion part of the airport. Which most likely we will have another meter (total of two, one for each transformer).


When you said "the same service" did you mean the primary feed for the transformers?
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When talking in NEC terminology the service starts at the point where utility ownership and maintenance changes over to customer ownership and maintenance.

See "Service Point" in art 100 definitions. If service point is on load side of both transformers then both systems are services and two services are allowed if they have different characteristics like these do.

If the transformers are customer owned then the service point is likely somewhere in the primary wiring to the transformers and that means the service actually is the medium voltage system, and the transformer secondaries are separately derived systems.
 
I haven't looked in a while, but code did allow an exception when the other service is a different voltage or configuration, since the new service meets this criteria, I would believe it to be legal.
 
faresos said:
We have an existing facility (small air port) that is served from 2000A, 208/120V service. The user wants to expand the building. There are many large loads to be added and served from 480V system such as Jet Bridge (total of 175KVA), 5 Ground Power units and HVAC equipment. Can we provide a 480v service for the expansion part? In another word, this building will be served from 208/120V (existing service) and new 480/277V service. Thanks,
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Just slightly off subject - what is the code section that requires plaque indicating 2 different voltage systems in the bldg [i.e. color code the 2 voltage systems]....I'm drawing a blank and can't find the section.
 
mistermudd said:
NEC 210.5 (C) Identification for Branch Circuits....Ungrounded conductors
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That section applies when there is more than one voltage system no matter what the sources are.

The question here is whether or not it is permitted to supply each system via services, or must you supply one service and separately derive the other system.
 
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