Well, if they (PoCo) utilize the existing 25KVA Transformer for a new 3Ø setup, it could be used, in addition to 2 more 25KVA Transformers, for a 75KVA 208Y/120V 3Ø 4 Wire Wye system.
For a Delta (which is what used to be commonly setup for Residential / Commercial shared customer power), the 25KVA Transformer might become the "Kicker" Transformer on an Open Delta Vee 4 wire setup - with like a 75KVA Transformer used for the "Main" Transformer.
If a closed Delta, they may use the 25KVA on an "End", with an additional 25KVA on the "Other end" - and place maybe a 37.5 or 50KVA in the center.
Chances are they will setup a 4 wire Wye. They might do an Open Delta Vee (around here, this is only for special conditions).
The Electrical Service / Design Manuals from SCE, PG&E, SDG&E, LADWP + Anaheim Water & Power describe that anything in the "Delta Flavors" for non-industrial / heavy commercial, or coming close to a residential / light commercial shared system, is not going to happen.
They will only give 4 wire Wye systems - even though there will be 1Ø 3 Wire Residential customers using this system too.
There are only a few exceptions to this "rule", and they all cover replacements of existing systems.
So to sum things up, I would expect the PoCo to create a 4 wire Wye system, then connect everyone on the Residential side to this, give your shop a 4 wire Wye service drop + meter, and be done with everything.
They can use the existing 25KVA Transformer, and add two more, which will create a 75KVA 208Y/120V 3 Phase 4 Wire Wye system.
Question:
How much do they (the PoCo) want to do this upgrade?
Are there any poles close to your shop, which have a 3 Phase system currently setup?
Do your Load Calcs call for 75KVA or higher?
Scott35
P.S. Unless the Houses which will share the system are very large - all electric, and each one has a home wood working shop that is used a lot, don't worry too much about them effecting the total capacity of the new Polyphase setup.
S.E.T.
