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Old 10-25-2012, 03:00 PM   #1
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208 volt delta transformer or 208V Y


is 208 a volt delta transformer used , if the service is going to be 280/120V-3P-4W and would like 480/277V-3P4W or will you need a 208 Y to 480/277 WYE transformer?

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Old 10-25-2012, 06:41 PM   #2
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208 volt delta transformer or 208V Y


If you want 277/480 and you have 120/208, the best transformer would have a 208 delta primary and a 277/480 wye secondary.

With this transformer, you'd need only the 3 phase wires from the 208 system, not the neutral. The 480 side would have 3 phase wires plus the neutral. Do not connect the neutral from the 208 system to the neutral of the 480 system. The ground is the only connection between the two.

Rob

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Old 10-25-2012, 06:47 PM   #3
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208 volt delta transformer or 208V Y


Quote:
Originally Posted by micromind View Post
If you want 277/480 and you have 120/208, the best transformer would have a 208 delta primary and a 277/480 wye secondary.

With this transformer, you'd need only the 3 phase wires from the 208 system, not the neutral. The 480 side would have 3 phase wires plus the neutral. Do not connect the neutral from the 208 system to the neutral of the 480 system. The ground is the only connection between the two.
The NEC (and safety) requires that the secondary neutral be bonded to ground. Thus, the primary and secondary neutrals will be connected to each other through their respective bonds to ground.

It's generally considered best to use a delta primary and wye secondary. If you use a wye primary though, you must connect the neutral - you can't leave it floating.
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