Stepping down to 208V

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stuartdmc said:
I need to step down from a 400A 120/240V 3 phase system to a 400A a 120/208V 3 phase system.
Any suggestions on what type of equipment will step this down?
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Wait a minute I thought we cleared this up the other day that ther are no such thing as 120/240volt 3 phase services exept for the ones with a high leg delta. Is that what this one is?
 
I believe Marc is right. 208 is the phase to phase voltage of a Y-connected three phase transformer, usualy stepped down from a 480 primary, and not usualy seen in residential stuff.
 
iaov said:
I believe Marc is right. 208 is the phase to phase voltage of a Y-connected three phase transformer, usualy stepped down from a 480 primary, and not usualy seen in residential stuff.
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who said anything about residential? I haven't seen that word so far on this thread.
 
WaMu has vary stringent engineered specifications and has refused to except the 240 volt system that is currently in the building. They want me to bring in a new 208v service which if brought in would cause a delay in the project. If I have to bring in a new service from the street, LA DWP won?t be able to install it until after the first of the year , moreover, WaMu wants to be opened by Dec.1st.
 
stuartdmc said:
I need to step down from a 400A 120/240V 3 phase system to a 400A a 120/208V 3 phase system.
Any suggestions on what type of equipment will step this down?
Click to expand...

No step down is involved. You need to change from a 240/120V delta system to a 208Y/120V wye system. Purchase a new full size transformer.
 
lets see if there is still a WaMu by the time the transformer comes in. This might be one of those self correcting problems.....
 
I presume that the supply transformer is owned by the power company, so that Jim's solution (replace the transformer with the correct one) gets translated to 'Wait for the power company to provide the correct service.'

I would not attempt to use 'buck-boost' or autotransformers, because the necessary symmetry around the grounded neutral renders standard buck-boost approaches useless.

Barring getting the POCO to provide the proper service, the only way you can get the specified 208/120V is with a suitable 'isolation' transformer. By 'isolation' I don't mean a special transformer, just one that has separate primary and secondary circuits.

Is it possible that the transformer bank feeding the current service could be re-configured to provide the desired 208/120V service? My understanding (not from direct experience) is that some standard POCO 120/240V single phase transformers can be reconnected as 120V transformers, and that a bank of three such transformers could be connected to provide a 240/120V high leg delta _or_ a 208/120V wye system. Perhaps the POCO can 'convert' the current service faster than they can provide a new service.

-Jon
 
winnie said:
I presume that the supply transformer is owned by the power company, so that Jim's solution (replace the transformer with the correct one) gets translated to 'Wait for the power company to provide the correct service.'
Click to expand...

You could purchase your very own 240 delta - 208Y/120 transformer if you cannot get it from the POCO, anything except a buck-boost.
 
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