3 Phase service question, need some expert advice

[Frank Walker]

I was designing an upgrade to the service at a local boat building plant (probably about 15 years back). Existing service was 120/240 3 phase closed delta (three phase primary with three transformers). The plant manager asked if we could shift over to 120/208. I told him probably not but I would call a few equipment mfgs and see what they had to say. Some said no problem, some said no, Ingersoll Rand (100 HP air compressors) said not only no but He** no. Only your equipment supplier can answer your question with any confidence.

We just upgraded the original delta service and it operated fine until they closed during the financial crisis. Utility was Gulf Power (Southern Co.). Don't think they would install a new closed delta system today, but I suspect they still use the open delta for the specific case I mentioned (one/ two 3 phase HVAC systems and the rest single phase).


L F Walker PER (professional engineer retired)

[Joe Jensen]

I bit more info. The lot is 132 wide by 253 deep. The utility says they have "3-phase lines" running under the east property line, North to south, on the 253 foot long side. If I do the 208V version I would need to pay to run wire 132 feet west to east and then maybe 200 feet south to the wall towards the front of the property to a meter, and then back north 50 feet to the shop. With the 240V option I would only have to pay to run 75 ft of wire. I am waiting for quotes from the utility for the 208V option. The 400A on the 240V version I would pay for 2 transformers and installation for a total of $3400.

[Rollie Meyers]

What voltage is the equipment that is going to be used? Motors rated for 230V cannot be supplied w/ 208V, & be code compliant, although buck/boost transformer(s) take care of that issue, older vintage motors rated 220/440V, 208-220/440V, will do fine on either 208V, or 240V, more modern 208-230/460V or current rated 200-230/460V will do fine on 208V or 240V also. This will dictate what is needed but my preference would be 208Y/120V, but having a lot of 230/240V equipment could make it rather expensive installing transformers to buck the voltage down to accommodate the 208V supply.

[Chris Hachet]

Can you get 480/277y service instead? It makes everything so much easier. I have 480 service, transformer to get 240v 3phase, transformer from 480 to my 240/120 single phase. I hate boosting voltage if I don't have to.

I would agree with Darcy.

[Joe Jensen]

Can you get 480/277y service instead? It makes everything so much easier. I have 480 service, transformer to get 240v 3phase, transformer from 480 to my 240/120 single phase. I hate boosting voltage if I don't have to.

I can only get 208 or 240 unfortunately