3 Phase Service Balancing

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Samuel Petrie

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Location
Abbotsford WI
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Electrician
We are currently working on an existing 600-amp 1 phase service; we are installing a new 600 amp 3-phase 480-volt service.
The utility doesn't know what the required maximum phase imbalance % is.
I'm trying to determine the number of transformers to install at the service point, as we are not being tasked with a complete rewiring of the facility at this time.
I'm curious if anyone has any good information to share on this subject.
 
What kind of service are you seeking WYE or DELTA? Or is this what you are trying to figure out.
 
No I’m trying to figure out if I need to use 6 transformers or I can use 3 transformers. I have a 600 amp single phase panel board that’s existing with 6-200 amp branch breakers. These branch circuits will be very lightly used once we have the 480 volt 3 phase installed. Just trying to determine if we need 3 transformers (each feeding 2-200 amp circuits) or I have to do 6 1 for each.
 
This is confusing without a lot more info.

Are we to assume the existing service and panel is 120/240?

Do you have 240V loads that can't operate at 208V?

What is the purpose of switching to a 480V 3-phase service? Is it a wye service? Why not get a 208V service?

If your goal is to transform the 480V back to 120/240V for the existing panels, then there's no reason you need 6 transformers. It sounds like you could have 3 of double the rating, and balance the feeder breakers as best you can.

Also on terminology:
It doesn't sound like you are installing transformers at the service point. And it sounds like the 6 200A breakers are feeders, not branch circuits.
 
jaggedben said:
This is confusing without a lot more info.

Are we to assume the existing service and panel is 120/240?

Do you have 240V loads that can't operate at 208V?

What is the purpose of switching to a 480V 3-phase service? Is it a wye service? Why not get a 208V service?

If your goal is to transform the 480V back to 120/240V for the existing panels, then there's no reason you need 6 transformers. It sounds like you could have 3 of double the rating, and balance the feeder breakers as best you can.

Also on terminology:
It doesn't sound like you are installing transformers at the service point. And it sounds like the 6 200A breakers are feeders, not branch circuits.
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My mistake on terminology, your correct that the branch breakers would actually be feeder breakers. The main reason to not use 120/208 volts is the fact any 240 volt 1-phase existing circuits would then not be the correct size depending on each circuit. We are attempting to make this as clean as possible.

The reason to make it 480 3-phase is the utility required it be switched out in order to add a new service for a different building at the same location.
When we ordered all the gear (minus transformers), there was to be a fair amount of load still on this old service (all 240 1-phase).
As the project has progressed along for various reasons all the major loads have been moved to a j
 
If your goal is to maximally balance your 6 circuits of 120/240V single phase loads on your new 480V 3 phase service, then you would need 3 single phase 480:120/240 transformers.

I don't see how using 6 separate transformers for each of your single phase loads would improve balance.

However keep in mind that the various 200A single phase loads may not be equivalent.

Jon
 
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