Why use a delta tranformer in this case....why not a wye?

[GoldDigger]

Yes, but that's not a true wye configuration. The OP was asking why he couldn't just mount a 240V wye transformer and get three 120V sources, phase to neutral.

That is why the short designation was written 208YY instead of 208Y.

 

[ggunn]

That is why the short designation was written 208YY instead of 208Y.

I'm still wrestling with the concept of grounding all three of the center taps. It seems to me that they should have voltage potential between them.

 

[GoldDigger]

I'm still wrestling with the concept of grounding all three of the center taps. It seems to me that they should have voltage potential between them.

Not when each secondary is isolated to start with.
You could not do it with a single xformer with the winding ends connected internally.
(as either wye or delta )

 

[Duncan8943]

Transformer Load Balancing with a high leg in each panel

Transformer Load Balancing with a high leg in each panel

We have a 300 kva transformer--high leg delta 240/120 supplying power to this facility. There are 5 single phase generator ATS (2 pole switches) and 5 panelboards. It looks to me that in order to balance the load on the transformer and ensure that you don't ever backfeed into the utility that you would have to use 5 single phase panelboards each having the high leg and another phase on it. Is there anything reason why it can't be done this way?

 

[Smart $]

We have a 300 kva transformer--high leg delta 240/120 supplying power to this facility. There are 5 single phase generator ATS (2 pole switches) and 5 panelboards. It looks to me that in order to balance the load on the transformer and ensure that you don't ever backfeed into the utility that you would have to use 5 single phase panelboards each having the high leg and another phase on it. Is there anything reason why it can't be done this way?

I can't think of any compliance issues... but I'm not agreeing with each panel having a high leg. I would think there'd be at least one or two with A and C.

 

[templdl]

I've got an assisted living facility which is classified as residential. Their are five 200A panels servicing the facility. Everything is single phase 120/240 VAC. Why would the previous electricians have requested that the utility transformer be a delta with a 208 VAC high leg? My line of thinking is that now I have a high leg that if I really wanted to take advantage of it then I would have to purchase 3 phase panels and pull additional wire and for what benefit. Not to mention the unused spaces in the panel that I would have liked to use for 120VAC circuits but cant because they would be 208VAC. Why wouldn't you get a 120/240 VAC 3 phase wye transformer?

It could be because of a phase shift issue.

 

[Duncan8943]

I can't think of any compliance issues... but I'm not agreeing with each panel having a high leg. I would think there'd be at least one or two with A and C.

You're right. I would have to look at the 120VAC lighting load on A&C and determine what I can put on it to balance it out.

 

[Duncan8943]

To avoid all of the open spaces in the panel boards that can be created by having the high leg, How about this idea: Use a 120/208Y transformer. All of the neutral to phase voltages will be 120V. Use 208/230V equipment. I still have the 120/240VAC single phase generators. Each panelboard is still a single phase with the difference that I have 240V when operating under generator power versus 208 when not. Any issues this?

 

[Smart $]

To avoid all of the open spaces in the panel boards that can be created by having the high leg.

That's why you run A & C to the panel(s) with 120V loads. No open spaces. Use panels with high leg for line-to-line loads. You can still power line-to-line loads with the A&C panel(s).

How about this idea: Use a 120/208Y transformer. All of the neutral to phase voltages will be 120V. Use 208/230V equipment. I still have the 120/240VAC single phase generators. Each panelboard is still a single phase with the difference that I have 240V when operating under generator power versus 208 when not. Any issues this?

If you do this with a system that was previously 120/240 1?, you'll have to verify none of the circuits have an undersized neutral. The neutral current on a 120/208 1? 3W system does not balance out like 120/240. In fact it is typically as high as, possibly even higher than the line currents.