Transfomer 208-480

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pakidiez

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Miami, FL US
Hello, I have a transformer that reads primary voltage is 208Y and secondary voltage is 480D.
The power I have in the building is 240D High Leg.
Does anybody know if I can input 240D into the 208Y or I need to buy one specifically designed for 240/480?
The electrician that service my building says it is still OK but he never did it before.
 
1. The 240V might drive the 208 winding into core saturation. Not likely, but possible.
2. Your output will be 553V. Not good!

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electrofelon said:
I am guessing the primary is actually the 480 side, as a wye-delta is an odd ball in the low voltage world. Transformers can usually be reverse fed, but if the voltage is wrong it's a moot point anyway.
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Ever since the NEC added the rule that you can't reverse feed a transformer unless it's listed for it I think some manufacturers have just been re labeling some of their transformers.
 
ActionDave said:
Ever since the NEC added the rule that you can't reverse feed a transformer unless it's listed for it I think some manufacturers have just been re labeling some of their transformers.
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450.11(B) stops well short of requiring that the transformer be listed for reverse feed. It only requires that the manufacturer's instructions permit reverse feed. A number of manufacturers have blanket instructions in their transformer catalog that permit a reverse feed.
 
don_resqcapt19 said:
450.11(B) stops well short of requiring that the transformer be listed for reverse feed. It only requires that the manufacturer's instructions permit reverse feed. A number of manufacturers have blanket instructions in their transformer catalog that permit a reverse feed.
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And a lot of them do not. We just installed a PV system that is 1000' from the service using a pair if 240V/2000V transformers. They came from the manufacturer with specific instructions as to which was the step up and which was the step down tranny.
 
GoldDigger said:
1. The 240V might drive the 208 winding into core saturation. Not likely, but possible.
2. Your output will be 553V. Not good!

Sent from my XT1585 using Tapatalk
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Around here typical no load voltage of a 240 volt service will be 247-252 volts driving the output even higher.
 
Aside from the voltage issue, having a 480V delta system presents a new set of potential problems as well; it needs to be corner gounded OR if left ungrounded, you have to add a ground fault monitoring system, all breakers and any other components must be rated for straight 480V, not "slash rated" as 480/277, anything with VFDs may not be capable of being connected and/or may not survive if they are.

If you need 480V and you have 240V, go hire a licensed electrician and have them buy you the correct transformer: 240V Delta to 480Y277, with factory documentation indicating that it is suitable for step-up. Skimping and trying to cobble together something from scrap parts will get everyone in trouble.

That said, I am closing this thread in accordance with the Forum Rules.

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