240 to 208

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dvcraven0522

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St. Louis, Missouri
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Working on a restaurant project that currently has 120/240. Project was designed for 120/208. I assume the 240V is a grounded B which has its own set of issues for some loads. I would like to suggest the contractor install a 240 delta-208/120 wye transformer. I would appreciate your thoughts and thanks.

Dan Craven
 
Are you sure you have a corner grounded B phase or do you have a high leg delta?

If you do have a high leg then anything 120V will work as long as you're careful to stay away from line to neutral on the high leg and anything using line to line loads would likely work on 240V or 208V.
 
I would suggest looking at the specific equipment. Some equipment might work on either 240 or 208 and you already have adequate 120.
The equipment that requires 208 might be adapted to a buck-n-boost transformer at less expense.
 
I would say first thing is to determine what your voltage configuration is before you do anything. Don’t assume. You order a transformer, or connect something and have the configuration wrong you could end up buying some expensive equipment.
 
dvcraven0522 said:
Working on a restaurant project that currently has 120/240. Project was designed for 120/208. I assume the 240V is a grounded B which has its own set of issues for some loads. I would like to suggest the contractor install a 240 delta-208/120 wye transformer. I would appreciate your thoughts and thanks.

Dan Craven
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I think that is probably the simplest if not the cheapest solution. It might even be the most cost effective solution.
 
As others have said, it’s probably not a corner grounded delta, most likely a delta with the center tap on one of the transformers grounded. If two transformers, it is an open delta, if three, it is a full delta. If the restaurant is the only load on that bank of transformers, it may be cheaper, and definitely more efficient to have the poco change the bank to a wye. (Unless there is only two of three phases coming onto the property, which it will be an open delta)
 
What will it take to have POCO change the supply to 208/120? Might be easier to bite the bullet on that if necessary than to have a transformer?
Will be a one time fee and POCO will maintain or replace transformer when necessary where owner will need to otherwise replace transformer if needed someday, plus it will give off heat which is real kW loss and will also increase AC load because of it.

This may be easier if the restaurant is only customer on the transformer. If transformer is serving multiple customers they may not be as willing to make such a change or it will cost if you really want to do so.

Or if limited number of items really need 208 maybe just use buck/boost transformers for those items?
 
kwired said:
What will it take to have POCO change the supply to 208/120? Might be easier to bite the bullet on that if necessary than to have a transformer?
Will be a one time fee and POCO will maintain or replace transformer when necessary where owner will need to otherwise replace transformer if needed someday, plus it will give off heat which is real kW loss and will also increase AC load because of it.

This may be easier if the restaurant is only customer on the transformer. If transformer is serving multiple customers they may not be as willing to make such a change or it will cost if you really want to do so.

Or if limited number of items really need 208 maybe just use buck/boost transformers for those items?
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That’s what I was thinking in an earlier post, usually restaurants have at least a 400 amp service, so it would be a large transformer.
 
hillbilly1 said:
That’s what I was thinking in an earlier post, usually restaurants have at least a 400 amp service, so it would be a large transformer.
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Might also want to watch out for situation where majority of load was single phase 120/240 with maybe somewhat limited three phase loads and supply is open delta with smaller pot for high leg.
 
I would just keep the 240 and roll with it, happens to me all the time.
you can really use 240 for lots of things without changing equipment, including LED lighting.
I have had to change elements on a fryer before, must most other equipment does not care.
 
tortuga said:
I would just keep the 240 and roll with it, happens to me all the time.
you can really use 240 for lots of things without changing equipment, including LED lighting.
I have had to change elements on a fryer before, must most other equipment does not care.
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Depending on the equipment, might cost same or even less to install buck boost there.

But I agree a lot of said equipment will operate at either 208 or 240 just fine.
 
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