[DollhouseDoc]

I wish to switch from delta to star (Y) 3 phase so I can eliminate 110v transformers. Motor capacity isn't an issue. Is there any wiring or code issue to consider?

[hfcarson]

Doc,
Your question is still a bit vague...
Are you going to have the utility make these changes or is this transformer
Under your ownership?
Does the existing Delta set-up have a high leg, (B phase)? Or do you have a grounded phase?

Depending on your existing set-up there are a few things that will require adjustment...

[DollhouseDoc]

What I have right now is three wires that can deliver 240 nom between each lead, but each lead to ground is an unpredictable and un-usable condition. So I can get single phase 240, but not 110 (I have a transformer to generate the 110 that is being used, which draws 3.9A when not loaded... that is what I want to change).

The utility owns the line transformers.

Thanks for answering

[hfcarson]

What you are describing is an "ungrounded" delta...
I assume you are not in the US? This type of service is rare and usually only
Found in industrial environments.

So, if the utility can rewire their existing equipment or otherwise provide you with a 208/120V, grounded Wye, it is likely that you will end up 208 volts phase to phase. For the most part this should not be an issue although some more sensitive and possibly older equipment may not operate as efficiently on the lower voltage so buck-boost transformers may be necessary.

Do your existing panels have neutral conductors? I assume not and therefor you will need to install grounded conductors into your distribution system...

Are you hiring a professional? If so, I would expect all the above be fairly well known.

[DollhouseDoc]

This is a very old industrial shed in the US. The single phase in the building is all in a grounded panel that is run by an old and humming transformer that is drawing 3.9A @240 24/7 and, as the facility is only used for warehousing with intermittant lighting any more, the 800A delta 3phase service isn't of much use. We will be switching it to Wye 3 phase or to single phase for our own use, but (all things being equal) would like to be able to retain the main for future possabilities.

Thanks for your answer. I surmise from it that the 3 hot legs of Wye 3 phase can be used for the 3 hot legs of delta with the only consideration being loss of horsepower in motors, and that no re-wiring will be necessary for the 3 phase items. I also expect that one leg to ground can feed one side of the single phase panel, and another leg to ground can feed the other side.

I am an industrial engineer with considerable wiring experience, but am at the edge of my experience with the big-wire stuff. And, If I can't intelligently oversee the process I won't know if it is done right. So, thanks again!

[hfcarson]

Hi Doc...
Yes, now I see where you are...
If the system is a "true" ungrounded delta system there should be "ground fault" detectors connected to the main distribution...
Either way, I do strongly recommend altering your incoming distribution. With 208V Wye you will get three phases each 208V between phases and each 120V to ground... far safer than what I think you might have now.

You wouldn't happen to be in the Phila Pa area?. just curious...