Forgot to ask the Original Poster ("OP") a few questions:
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[*] Are the Tenant Suites to be "Separately Metered"?,
[*] How many "Leasable" Square Feet are on each floor?,
[*] Does your location have any Energy Conservation Codes?,
[*] Did the PoCo (Power Company) Service Engineer quote that they would supply this project with a 2500 KVA Transformer, or is this what your client would like to have?
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The idea of 12 KV distribution on a 4 floor Office Structure, would be something done "Long Ago" in my areas.
I have seen older projects with Medium Voltage Distribution, but these were in old Downtown L.A. Buildings.
The Electrical Rooms were designed for >2000 VAC Systems, which contained 12,470 VAC to 480 VAC Transformers in one vaulted area, and the Low Voltage Gear, Panelboards + 480V x 240V & 480V x 208Y/120V Transformers in another area of the same Electrical Room(s).
Currently, I do not think the KVA requirements of your Project would be ample to warrant the use of anything above a 600 VAC Service Voltage; but that's judging from what is common in my area (Southern California).
If the Tenants' Suites will be separately metered, then you might be looking at a Service Voltage of 208Y/120V 3Ø 4 Wire.
If everything will be from a single meter, then the 480Y277V 3Ø 4 Wire Service is the best choice.
As to the possible Energy Conservation Codes, you will need to allow each tenant's space to have lighting controls dedicated to them only. Verify this with your local Building Department, to find out what is involved for compliance.
If this project is in California, let me know, and I will post the necessary links to obtain compliance manuals and sheets.
I will check back for your reply.
Scott35
