Delta Transformer- 3-Phase, 4-Wire

[faresos]

Hello everyone:

is it common that the utility can distribute 240/120V, single phase (for residential loads) from Delta 3-Ph, 4-Wire transformer? I have a situation where the utility wants to provide a 240V/120V single phase service to 5-trailers each will require (150A, 240/120V, 1-ph). Since the only way to get 120/240V service is from the A-C & neutral (center tap). I have additional questions:

1. Does the main service distribution panel needs to be 240V, 3-Ph, 4-wire, and we only use the C-A phase & neutral to serve all these loads? Or the main distribution panel service needs to be single phase since it will only utilize C-A phase & neutral?
2. My understanding for the 240/120V, 3Ph, 4-W system we can't have 120V loads more than 5% of the transformer rated KVA and I'm sure this will exceed that but the utility co saying they have no concerns of that. Is this accurate statement?

Thanks in advance!

 

[ActionDave]

I usually see this happen the other way around- it is easier for the utility to set somebody up with three phase power in an area that is predominantly single phase by using a delta system because all they need to do is add a transformer.

A to C phase on a delta is the same as a 120/240 single phase system so I would think the utility would be able to set you up with a single phase service and you would not even know that it is being fed from a delta transformer bank on their end.

 

[faresos]

I usually see this happen the other way around- it is easier for the utility to set somebody up with three phase power in an area that is predominantly single phase by using a delta system because all they need to do is add a transformer.

A to C phase on a delta is the same as a 120/240 single phase system so I would think the utility would be able to set you up with a single phase service and you would not even know that it is being fed from a delta transformer bank on their end.

so does my main service distribution panel (which will provide power to 5-trailers) will need to be a single phase?

 

[ActionDave]

I would say yes, but I am not seeing the whole picture.

 

[augie47]

Also, not seeing the whole picture, I agree with ActionDave.
Its certainly not too uncommon in this area to find a or several single phase loads connected to the A-C phase of a POCO 3 phase back where they have added a pot for a small 3 phase load.
You should be able to build your service(s) as if there is no 3rd phase.

As far as part (2). It is my understanding that the 5% neutral limit is not applicable to POCO design using individual transformers.

 

[Ingenieur]

Hello everyone:

is it common that the utility can distribute 240/120V, single phase (for residential loads) from Delta 3-Ph, 4-Wire transformer? I have a situation where the utility wants to provide a 240V/120V single phase service to 5-trailers each will require (150A, 240/120V, 1-ph). Since the only way to get 120/240V service is from the A-C & neutral (center tap). I have additional questions:

1. Does the main service distribution panel needs to be 240V, 3-Ph, 4-wire, and we only use the C-A phase & neutral to serve all these loads? Or the main distribution panel service needs to be single phase since it will only utilize C-A phase & neutral?
2. My understanding for the 240/120V, 3Ph, 4-W system we can't have 120V loads more than 5% of the transformer rated KVA and I'm sure this will exceed that but the utility co saying they have no concerns of that. Is this accurate statement?

Thanks in advance!

1 each trailer will have a pnl
are you saying you will have an mdp/meter bank feeding these
either way I would guess 120/240/1 ph

2 the majority of the loads will be 240
hvac, dryer, water heater, range
not sure the 120 will be less than 5% but should be low
if you use 1/3 of the xfmr and your 120 is 30% of your total it is only 10% of the total xfmr capacity
what does it matter anyways? If they say ok, it's ok lol

 

[meternerd]

More commonly done with 120/208 Wye. Used when an apartment complex may have 120/208 4WY and a next door neighbor needs 120/240 single phase. You just use a larger single phase 120/240 transformer to supply the neighbor and use a leg of the 120 to feed a third leg of the 120/208 load. Easier to see with a drawing, but I don't know how to attach drawings.

 

[kwired]

2. My understanding for the 240/120V, 3Ph, 4-W system we can't have 120V loads more than 5% of the transformer rated KVA and I'm sure this will exceed that but the utility co saying they have no concerns of that. Is this accurate statement?

Thanks in advance!

That mostly only applies to units where the coils are all on a single core. If you have a bank of individual single phase transformers, the 120/240 pot is sort of stand alone as it relates to your use, and should be able to deliver half it's kVA rating for a A or C to N load or it's full rating to A to C as well as balanced A-N-C loads.