Wye to delta labeling

[Volta]

Three old single phase transformers, 120 primary, 120/240 secondary. 25 kVA each. Wired as 208/120 wye primary, 240 high-leg delta secondary. They feed a 200(225) amp panel.

Wired wrong in a few different ways now. Among other problems, the primary and secondary ties are #4 and #3, respectively. Line and load are 3/0, which is ok. One tie for the primary neutral is severely overheated. I want to remove the entire bank. The transformers are too small to use the proper wire and lugs. The customer can live without the delta system.

The panel it feeds (circa 1969) is a SqD NQOB delta panel. It has 52 spaces, bottom feed, three phase only on the lower 18 or so spaces, then only phase A and C extending to the upper part. It has a regular SqD label that says 240 volt delta on it.

I would like to feed this directly from the 208/120 volt building system. I am ok with the voltage change, electrically [110.4, 240.83(E)].

Could it be that instructions exist(ed) for this panel that would require is use only on a delta system [110.3(B)]? It is obvious that is what it was made for, and is labeled that way.

Should it pass inspection as 208 wye?

 

[LarryFine]

Thoughts:

You should make sure the primary neutral point is floating, i.e., not tied to the supply neutral. It should be wired as though it was a Delta load.

The 3-ph loads, and any 1-ph line-to-line loads, in the Delta panel must be able to run on 208v.

The worst thing about using this panel is the inability to easily balance the loading.

As for passing, simply ask the pass-or-fail'er.

 

[Volta]

Thoughts:

You should make sure the primary neutral point is floating, i.e., not tied to the supply neutral. It should be wired as though it was a Delta load.

I know, but they are tied together now. That is one of the problems, ends-up being a autotransformer set-up. I didn't think that was the cause of the overheated #4 conductor at first, but do you think that is a large contributing factor?
View attachment 4284

The 3-ph loads, and any 1-ph line-to-line loads, in the Delta panel must be able to run on 208v.

So far everything should be ok. My customer is buying this existing building and the original equipment is gone. I had fed a new sub-panel already from this panel before I ever saw the problems in the trans, but only have two inductive loads fed from the new sub. Their machines have been running for years at 200 volts or so, but I wanted to get it closer to the nameplates while we had the chance.

The worst thing about using this panel is the inability to easily balance the loading.

Yeah, but that is true as it is too.

As for passing, simply ask the pass-or-fail'er.

I guess I'll need to, just looking for your opinions first!