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Old 10-09-2007, 08:48 PM   #1
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Default transformer reverse wiring

This concerns delta corner grounding
I have a 480 - 120/208 transformer.
I want to derive 480 volts.
I will feed a 30 kva with a 90 amp breaker and feed the L 123 lugs
I then will take H 123 for my load.
My question is do I corner ground one of the 3 H legs to produce stable voltage readings?

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Old 10-10-2007, 05:48 PM   #2
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[quote]I will feed a 30 kva with a 90 amp breaker and feed the L 123 lugs
I then will take H 123 for my load. [quote]

I assume you mean X1, X2. X3 are 208 (no neutral/grounded conductor)and H1, H2, H3 480 VAC?

That is up to you the NEC does not require it.

BUT IMO, this is a bad installation. I speak from a multitude of experience, where contractors call my shop to check out WIERD voltages at a facility we get there, and we find this connection. In addition some transformer manufactures do not list their transformer for reverse feeding. Lastly there is a higher inrush on the 208 VAC side then there would be on a 208 delta to 480/277 Wye due to winding design They make the right transformer for the application, why not use it? 208 Delta to 480/277 Wye.

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