Getting 1ph from a 3ph transformer

J

JoeNorm

Senior Member
Location
WA
I don't deal with 3ph much because I do mostly rural residential work.

I am working on a residence that has a 480/277v transformer on the property(not common around here) and the owner would like to get a single phase panel installed. Is this possible?

Don't worry, I don't plan on doing the work until I gather a lot more info. And even then I may end up calling in someone with more experience to handle this end of things. Just trying to figure out what is possible. Thanks, let me know what other info is needed to answer this question.
 
Yes, easy. Get either a 1ph 277-to-120/240v or a 1ph 480-to-120/240v transformer.

The former would add more load to one phase, while the latter less to two phases.
 
There is a large 480V panel fed from said transformer. There is a 100amp breaker in large panel that feeds a 120/240v 1ph panel next to it. Does that mean there must be a transformer somewhere?
 
Is this a utility owned transformer that provides 480/277V from the primary distribution, or is the utility bringing in something like 208/120 (or even 120/208) and a customer owned transformer that steps this up to 480/277V?

If the utility is providing 480/277V, then the choice is to use a 480V to 120/240V single phase transformer (or 277V primary), _or_ to have the utility drop a second 120/240V service. The first means the customer has to buy a transformer and pay for transformer losses, the second means the customer will have to pay the fees for two services. Which approach makes the most sense depends on the utility charges.

If the utility is providing 208/120V, then you probably want to just use that directly unless the customer really needs 120/240V single phase (rather than 208V); most residential loads can use either 120/240V or 120/208V.

-Jonathan
 
JoeNorm said:
Sounding more and more like the client will need a new 240/120 transformer installed by the POCO
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It’s unlikely that the PoCo will willingly install another transformer to a service drop that already has one, it’s typically the user responsibility to transform a 480V service down to 120/240 single phase (or 208Y120 3 phase) for lights and outlets.

But really, it’s no big deal. Almost EVERY 480V service has a step-down transformer on site for this purpose.
 
Why is there 480/277 to begin with? Something being converted from industrial/commercial to residential? Something that still is industrial/commercial yet adding a dwelling to it?

You can supply a 480 x 120/240 single phase transformer from it, whether you have capacity for the added load is hard to tell you without a bunch of additional information. Calculating size of that transformer would need to know details of what the dwelling has for loads.

There might already be some 120/240 single phase there, but would need to know what it's capacity is, the existing loads to be served as well as added load to be served to know if you can add on to it.

If a change of occupancy type and there is no longer going to be any need for 480 volt loads, you might be better off having POCO change the service 120/240 single phase or if still going to be somewhat significant load maybe to 208/120 three phase.
 
If you already have three phase, why would you want to install a single phase panel? I understand the need for the lower voltage, but my choice would be a 3 phase 480 to 208Y/120 volt transformer feeding a 3 phase panel.
 
don_resqcapt19 said:
If you already have three phase, why would you want to install a single phase panel? I understand the need for the lower voltage, but my choice would be a 3 phase 480 to 208Y/120 volt transformer feeding a 3 phase panel.
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Can depend on the load served? If this is a pretty small dwelling with no electric heat or water heating and gas cooking appliances as well, it may very well be capable of being served by a 5 to 10 kVA transformer, or even sub fed from 208/120 source that was mentioned that may already be present?

If going to be multiple dwellings 208/120 very well can be the smart way to go, maybe only send single phase feeder to each dwelling though.
 
kwired said:
Can depend on the load served? If this is a pretty small dwelling with no electric heat or water heating and gas cooking appliances as well, it may very well be capable of being served by a 5 to 10 kVA transformer, or even sub fed from 208/120 source that was mentioned that may already be present?

If going to be multiple dwellings 208/120 very well can be the smart way to go, maybe only send single phase feeder to each dwelling though.
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3, 6, and 9 kVA are standard 3 phase transformer sizes
 
don_resqcapt19 said:
3, 6, and 9 kVA are standard 3 phase transformer sizes
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3 kVA @208/120 probably wouldn't handle a 1500 120 volt watt appliance so well which you kind of need at least two SABC's that can handle that sort of load. Is kind of technically going to be undersized if supplied by 120/240 single phase as well though it maybe actually has a better chance of successfully handling it should you use one of those and there is literally very minimal load to this dwelling.
 
ptonsparky said:
How big is his single phase requirement?

Large panel means very little. You are not giving out pertinent information.
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True, I just haven't been back to the site to gather more details

Customer would like a 400amp service to serve two new areas of the property with options of adding dwellings
 
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