Delta high leg, or single phase 3 wire transformer for residential?

[BeeBrave]

In a commercial building with available 480V 3ph/4w, we are adding a single phase residential mock up area. What should the transformer configuration be?

Should it be: 240/120V, 3ph, 4w delta high leg transformer, with 480V 3 wire input?
Or, single phase 240/120V, 1ph, 3w transformer, with 240V 2 wire input?

Please explain the reasoning. Thanks.

 

[tom baker]

Not high leg for sure. You have to use full rated breakers (not slash), ie expensive, can't use the B phase, panel will be more expensive, requires additional labeling.
If resi, go with 120/240 single phase.

 

[LarryFine]

In a commercial building with available 480V 3ph/4w, we are adding a single phase residential mock up area. What should the transformer configuration be?

Should it be: 240/120V, 3ph, 4w delta high leg transformer, with 480V 3 wire input?
Or, single phase 240/120V, 1ph, 3w transformer, with 240V 2 wire input?

Please explain the reasoning. Thanks.

Welcome to the forum.

A single-phase unit with a 480v 2-wire primary (to suit the source) and a 120/240v 3-wire secondary (to suit the load.)

You only need a transformer that supplies what you need. Anything more is a waste of material and electricity.

 

[infinity]

In a commercial building with available 480V 3ph/4w, we are adding a single phase residential mock up area. What should the transformer configuration be?

Should it be: 240/120V, 3ph, 4w delta high leg transformer, with 480V 3 wire input?
Or, single phase 240/120V, 1ph, 3w transformer, with 240V 2 wire input?

Please explain the reasoning. Thanks.

For the residential mock up what is the voltage that you need? Is it 1Ø,120/240? Your primary should be 480 volts.

 

[BeeBrave]

For the residential mock up what is the voltage that you need? Is it 1Ø,120/240? Your primary should be 480 volts.

Rob,
The loads are 240/120V 1ph.
I meant to say:
"Or, single phase 240/120V, 1ph, 3w transformer, with 480V 2 wire input?"

I think a few people already answered this. If there are no 3 phase loads, there's no need for a delta transformer.
Thanks.

 

[BeeBrave]

Welcome to the forum.

A single-phase unit with a 480v 2-wire primary (to suit the source) and a 120/240v 3-wire secondary (to suit the load.)

You only need a transformer that supplies what you need. Anything more is a waste of material and electricity.

Larry,
Is there any merit to use delta 3 phase transformer, to balance the load upstream across 3 phases? Thanks.

 

[kwired]

208/120Y might be a reasonable option. More load details would make a difference in knowing if you should even consider three phase vs single phase. If pretty lightly loaded dwelling probably best to just go with the single phase 120/240.

 

[texie]

Larry,
Is there any merit to use delta 3 phase transformer, to balance the load upstream across 3 phases? Thanks.

Just keep it simple and use 480 single phase on the primary as Larry suggested. Remember, you will need the 120/240 side to have a GES and bonded neutral.

 

[LarryFine]

Larry,
Is there any merit to use delta 3 phase transformer, to balance the load upstream across 3 phases? Thanks.

Not really. A delta-delta transformer would simply pass the one loaded secondary's load to the single corresponding primary.

 

[winnie]

Short of something actually storing energy, you can't create balanced 3 phase loading from a single phase load.

If you have such a large residential mock up area that you need to be concerned about 3 phase balance (eg you are mocking up an entire block of houses running their HVAC equipment) then you should consider multiple 480:120/240 V single phase transformers on different primary phase sets.

If you are mocking up a huge electrical system for an apartment building or a billionaire's mansion, then use 3 phase 208/120.

Jon

 

[kwired]

Short of something actually storing energy, you can't create balanced 3 phase loading from a single phase load.

If you have such a large residential mock up area that you need to be concerned about 3 phase balance (eg you are mocking up an entire block of houses running their HVAC equipment) then you should consider multiple 480:120/240 V single phase transformers on different primary phase sets.

If you are mocking up a huge electrical system for an apartment building or a billionaire's mansion, then use 3 phase 208/120.

Jon

Yes, outside of HVAC equipment and/or common systems that are not part of individual units, the high leg will have little or no load that can be connected to it within individual units so won't do much for load balancing on the 480 volt supply to use a high leg delta anyway. But those systems not part of individual units possibly can be directly connected to the 480 system anyway.

 

[wildcat greg]

In a commercial building with available 480V 3ph/4w, we are adding a single phase residential mock up area. What should the transformer configuration be?

Should it be: 240/120V, 3ph, 4w delta high leg transformer, with 480V 3 wire input?
Or, single phase 240/120V, 1ph, 3w transformer, with 240V 2 wire input?

Please explain the reasoning. Thanks.

I would provide a three phase primary wye 480/277 volt transformer kva per load and a secondary wye 120/208 volt three phase for area to keep load balanced and reduce load on grounded conductor

 

[kwired]

I would provide a three phase primary wye 480/277 volt transformer kva per load and a secondary wye 120/208 volt three phase for area to keep load balanced and reduce load on grounded conductor

If you are using 480 volt two wire primary single phase transformers there isn't any load on the 277 neutral anyway.

 

[winnie]

A wye primary transformer is not appropriate in this application. Even when fed from a wye supply, a delta primary is almost always the correct choice for a three phase transformer not on the utility side of things.

As far as using a 208/120 wye secondary, that will provide better load balance on the 480V system, but will be a poorer 'mockup' of most residential single phase systems. The choice of 1 or 3 phase will depend upon the specific requirements of this 'mockup'.

Jon

 

[LarryFine]

As with any service, you start with the load to be served, and work your way back to the source.

In this case, "a single phase residential mock up area," so a 1ph, 120/240v panel is appropriate.