Can you use a wye transformer but not connect the neutral?

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cppoly

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To step up a 3 phase 208V to a 3 phase 480V, can you use a 208V delta to 480V wye transformer and just not connect the neutral? Is this allowed?
 
cppoly said:
To step up a 3 phase 208V to a 3 phase 480V, can you use a 208V delta to 480V wye transformer and just not connect the neutral? Is this allowed?
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If by not connect the neutral you mean not ground the neutral on the secondary side, the answer is probably yes short of the Transformer manufacturer requiring it for some reason. I can't think of a good reason to do it this way as you would have to add ground detectors on the secondary which would add cost and nuisance, but I think it would be legal code wise.
 
If you use the neutral (supply 277 volt loads) I think it is clear you must ground the neutral.

If not using the neutral for a circuit conductor, the rule isn't quite as clear.

It has been asked here before if you could ground a phase of a wye connected generator as a standyby system for a corner grounded delta. Not the same thing yet very similar.
 
Let me explain what I'm trying to do.

We have a 3 phase 208V supply and need 480V for a motor. Would it make sense to do 208V delta to 480V delta? Or do 208V delta to 480V wye (and just not connect the neutral since it is not needed for a motor load).
 
cppoly said:
Let me explain what I'm trying to do.

We have a 3 phase 208V supply and need 480V for a motor. Would it make sense to do 208V delta to 480V delta? Or do 208V delta to 480V wye (and just not connect the neutral since it is not needed for a motor load).
Click to expand...

If you haven't purchased the transformer get a 208 delta to 480 delta.
Then your electrician wont be calling asking what to do with XO.
 
cppoly said:
.... Or do 208V delta to 480V wye (and just not connect the neutral since it is not needed for a motor load).
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Yes. Do this.

A delta, wye step up transformer gets wired the same as a step down transformer. You bond the XO at the transformer or first disconnect and don't bring it to the motor, but you will have 277V to ground in case of a ground fault instead of 480V.
 
qcroanoke said:
If you haven't purchased the transformer get a 208 delta to 480 delta.
Then your electrician wont be calling asking what to do with XO.
Click to expand...

True, he won't be asking what to do with X0 but it will create a whole host of other code issues to consider that are far more complex than using a 208 delta X 480Y.
 
ActionDave said:
Yes. Do this.

A delta, wye step up transformer gets wired the same as a step down transformer. You bond the XO at the transformer or first disconnect and don't bring it to the motor, but you will have 277V to ground in case of a ground fault instead of 480V.
Click to expand...

And gotta attach XO to the GES, 250.30(A)(4) and (5) right?

Same place the bonding jumper for XO is connected.
 
Elevated voltage

Elevated voltage

You MUST ground the tranny and extend the SSBJ to your first switch.
If you do not, WHEN a fault occurs, there will be no path for the current to clear the fault, and you will have now a voltage on every grounded object in the building.
Sketch out the circuit diagram with a main bonding jumper and see what happens when you erase the SSBJ.
 
texie said:
True, he won't be asking what to do with X0 but it will create a whole host of other code issues to consider that are far more complex than using a 208 delta X 480Y.
Click to expand...

Thanks for the reality check...... Not gonna say I knew better but I do now.
 
texie said:
True, he won't be asking what to do with X0 but it will create a whole host of other code issues to consider that are far more complex than using a 208 delta X 480Y.
Click to expand...
I don't see what is so complex. The secondary needs to have a conductor grounded. Since the neutral isn't used as a circuit conductor you possibly may be able to ground a phase conductor, but why not bond the neutral and have 277 volts to ground instead of 480 - you won't use any more or less copper either way?

If you don't solidly ground one secondary conductor then you need a ground fault detection system, so unless it is a process that you want an orderly shut down if a fault occurs, you are going to spend less by grounding that system. High impedance ground is one other option if you do have a wye secondary, but has similar costs and issues as the ungrounded system.
 
texie said:
kwired said:
True, he won't be asking what to do with X0 but it will create a whole host of other code issues to consider that are far more complex than using a 208 delta X 480Y.
Click to expand...

I don't see what is so complex. The secondary needs to have a conductor grounded. Since the neutral isn't used as a circuit conductor you possibly may be able to ground a phase conductor, but why not bond the neutral and have 277 volts to ground instead of 480 - you won't use any more or less copper either way?

If you don't solidly ground one secondary conductor then you need a ground fault detection system, so unless it is a process that you want an orderly shut down if a fault occurs, you are going to spend less by grounding that system. High impedance ground is one other option if you do have a wye secondary, but has similar costs and issues as the ungrounded system.
Click to expand...
You are making texie's point that is simpler to ground the neutral of a wye secondary.
 
208 delta

208 delta

I never heard of a 208 volt delta transformer. could someone draw a diagram ?
 
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