Grounding Single Phase Transformer

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ActionDave said:
Is this a trick question?
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Well seeing as how your not going to buck 480 down to 277 and you don't have a neutral in the panel to begin with, if you stick a 1p breaker in a delta panel,,
what voltage are you starting with to be able to boost it to 277 ?

JAP>
 
shespuzzling said:
Thanks!

Yes 480V panel is a delta, no neutral which is why we need to add this little transformer.

The 277V winding does not have a center tap, we're literally taking the 480V phase conductors, transforming them down to 277V, and then would ground one end of the secondary and viola we have a neutral!

I just attempted to attach the cut sheet which should hopefully clarify what we're trying to do.
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You don't have a center tap on this transformer because the secondary output is a single voltage, not a dual voltage secondary where you'd find the "center tap" that your referring to.

JAP>
 
jap said:
Well seeing as how your not going to buck 480 down to 277 and you don't have a neutral in the panel to begin with, if you stick a 1p breaker in a delta panel,,
what voltage are you starting with to be able to boost it to 277 ?

JAP>
Click to expand...

Why would you stick a 1p breaker in a 3 wire delta panel?
 
ActionDave said:
Would the PTAC care if there is a neutral as long as the voltage is within spec? Seems like a buck/boost aka autotransformer would be fine.
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Likely not, then there is NEC requirements, I fairly certain the "common" conductor of the autotransformer needs to be a grounded conductor, though I have boosted 240 to 277 before for some HID lights that did not have multivolt taps and they worked fine.

jap said:
With a 480v delta panel, what voltage would you start with to be bucking or boosting from?

Jap>
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Corner grounded or ungrounded - 480 volts - not going to find a buck boost that will change the voltage that much, but if it were a high leg secondary - you do have two phases to neutral that are 240 volts and a 416 volt high leg. You could easily boost one of those 240 volt legs to 277 and even have a grounded common conductor.
 
kwired said:
Likely not, then there is NEC requirements, I fairly certain the "common" conductor of the autotransformer needs to be a grounded conductor, though I have boosted 240 to 277 before for some HID lights that did not have multivolt taps and they worked fine.

Corner grounded or ungrounded - 480 volts - not going to find a buck boost that will change the voltage that much, but if it were a high leg secondary - you do have two phases to neutral that are 240 volts and a 416 volt high leg. You could easily boost one of those 240 volt legs to 277 and even have a grounded common conductor.
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I don't disagree, it's just that producing that 277v voltage that way on a lighting load that is fixed may not be much of an issue.

I have found anyway, that the voltage floats a lot depending on the load with a buck/boost and in the OP"s scenario would feel that the grounded secondary would be the way to go but that's just me.

JAP>
 
jap said:
I don't disagree, it's just that producing that 277v voltage that way on a lighting load that is fixed may not be much of an issue.

I have found anyway, that the voltage floats a lot depending on the load with a buck/boost and in the OP"s scenario would feel that the grounded secondary would be the way to go but that's just me.

JAP>
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Voltage fluctuates with load in every kind of circuit.
 
ActionDave said:
If you wanted to buck 480V down to approximately 277V you would use a two pole breaker the same way you feed from a two pole breaker when you boost 208V up to approximately 240V.
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You don't end up with a true solid 277v circuit with a grounded neutral that way.
To me that's just a crappy way of doing things.

The transformer the OP posted is the ticket.
I just don't see why one wouldn't want to use it.

Oh well, to each his own.

JAP>
 
ActionDave said:
If you wanted to buck 480V down to approximately 277V you would use a two pole breaker the same way you feed from a two pole breaker when you boost 208V up to approximately 240V.
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Can you give me the part number of a buck/boost transformer that will buck 203 volts down from 480v 1ph to get to 277?

I'm interested.


JAP>
 
jap said:
You don't end up with a true solid 277v circuit with a grounded neutral that way.
To me that's just a crappy way of doing things.

The transformer the OP posted is the ticket.
I just don't see why one wouldn't want to use it.

Oh well, to each his own.

JAP>
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I agree the xformer in the op is a perfectly fine install, I'm just not seeing the issue with a buck boost other than it's not as conventional. You don't have a true grounded neutral in any straight 208V, 240V or 480V single phase circuit.
 
ActionDave said:
I agree the xformer in the op is a perfectly fine install, I'm just not seeing the issue with a buck boost other than it's not as conventional. You don't have a true grounded neutral in any straight 208V, 240V or 480V single phase circuit.
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A 277v circuit is not the same as a 208,240 or 480v circuit.

JAP>
 
jap said:
You don't end up with a true solid 277v circuit with a grounded neutral that way.
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You don't end up with a grounded neutral with either type of transformer.

You could end up with a grounded circuit conductor with both types of transformers. Or you could end up with an ungrounded circuit with both types of transformers.
 
ActionDave said:
I agree the xformer in the op is a perfectly fine install, I'm just not seeing the issue with a buck boost other than it's not as conventional.
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The problem with the buck boost isn't that it's not conventional, it's that it's not practical. If you got a transformer with custom winding voltages to buck 480 to 277, the transformer would be a larger kVA than the 1kVA isolation transformer in the OP.
 
david luchini said:
You don't end up with a grounded neutral with either type of transformer.

You could end up with a grounded circuit conductor with both types of transformers. Or you could end up with an ungrounded circuit with both types of transformers.
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There's no need to confuse the issue.

A buck boost transformer would not be the ideal choice in this instance.

JAP>
 
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