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I have120/208 at my Jobsite. I need 277/480 to supply a temp material hoist. My shop has a step down 480 primary to 208 secondary transformer. They want me to use this transformer and wire it reversed. My primary being my load for my hoist and my secondary being my line from my mdp. Voltages will still match the transformers rating. Just the line and load will be reversed. Any one installed a transformer this way? Any thoughts?
 

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You won't have a neutral on the (original) primary side, which will end up being your secondary.
 

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I have120/208 at my Jobsite. I need 277/480 to supply a temp material hoist. My shop has a step down 480 primary to 208 secondary transformer. They want me to use this transformer and wire it reversed. My primary being my load for my hoist and my secondary being my line from my mdp. Voltages will still match the transformers rating. Just the line and load will be reversed. Any one installed a transformer this way? Any thoughts?
All single phase?
 

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Discussion Starter #4
I understand that concept just wondering if i should be concerned with it going bad. Being wired differently
 

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1. You will only be able to feed 3 phase 480 VAC and single phase 480 VAC as Ken said no neutral.

Additionally you will need to corner ground the transformer or install ground alarms.

Higher inrush as noted, and a few other minor drawbacks

Or you could order a 208 delta to 480/277 wye.
 

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Don't bond "XO" if you choose to go this route. I removed these from 2 "back fed" xfmrs after a single phasing incident. The smoke from the melting insulation set off the F.A. in the building. Yes, the one on the left melted completely in two!


I am wondering why you wouldn't want to bond xo on the low side? I call it this for less confusion, but it still is wound as a wye. I always thought you still had to bond xo. Kinda confused now.
 

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brian john said:
1. You will only be able to feed 3 phase 480 VAC and single phase 480 VAC as Ken said no neutral.

Additionally you will need to corner ground the transformer or install ground alarms.

Higher inrush as noted, and a few other minor drawbacks

Or you could order a 208 delta to 480/277 wye.
Can you explain grounding the corner. What specific lugs get bonded to ground when this is done.
 

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I have120/208 at my Jobsite. I need 277/480 to supply a temp material hoist. My shop has a step down 480 primary to 208 secondary transformer. They want me to use this transformer and wire it reversed. My primary being my load for my hoist and my secondary being my line from my mdp. Voltages will still match the transformers rating. Just the line and load will be reversed. Any one installed a transformer this way? Any thoughts?
Never have done it but a transformer does not know if it is a step up...or a step down. Just wire it and if the current on your secondary is okay, all should be well.
 

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Don't bond "XO" if you choose to go this route. I removed these from 2 "back fed" xfmrs after a single phasing incident. The smoke from the melting insulation set off the F.A. in the building. Yes, the one on the left melted completely in two!


Yes, this is what can happen for sure.
 

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I am wondering why you wouldn't want to bond xo on the low side? I call it this for less confusion, but it still is wound as a wye. I always thought you still had to bond xo. Kinda confused now.
For one it is a code violation grounding a system down stream from the main neutral ground bond.

The current imbalance that can flow on this connection (I BELIEVE THIS IS WHY)exceeds the sizing requirements for the conductor.
 

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The current imbalance that can flow on this connection (I BELIEVE THIS IS WHY)exceeds the sizing requirements for the conductor.
I don't understand it fully but when you bond XO as long as the supply is either on or off things will be fine. But if the supply loses a phase the current starts to flow on the XO connection and yes at much higher current than that conductor is sized for. But even if it was sized larger you would not want (as you already know) current to be flowing on the bonding jumper to the GEC / EGCs.
 

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When hooking up a transformer backwards you do not bond the X0 or connect to the neutral. Some transformers have a label to remind you.
X1, X2 & X3 are your 208 inputs. H1, H2 & H3 are your 480 outputs.

Ground one output leg. You will have 0 volts, 480 volts & 480 volts to Ground. Will drive the lift repair man crazy unless he has seen a corner ground system.

You can order a 208 to 277/480 transformer to get your standard Y output.
 

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For one it is a code violation grounding a system down stream from the main neutral ground bond.

The current imbalance that can flow on this connection (I BELIEVE THIS IS WHY)exceeds the sizing requirements for the conductor.
But I am just set on thinking if you hook up a wye system and something happens to it, the only path is phase to phase. MAybe I should not have said to bond xo, but to bring neutral to it. Xfmers are not smart.they can deliver unlimited amps until they pretty much blow up or start on fire. I do agree on you with getting the right one for its intended use.
 

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But I am just set on thinking if you hook up a wye system and something happens to it, the only path is phase to phase. MAybe I should not have said to bond xo, but to bring neutral to it. Xfmers are not smart.they can deliver unlimited amps until they pretty much blow up or start on fire. I do agree on you with getting the right one for its intended use.
Transformers CANNOT deliver unlimited amps, they are limited on the primary by what the supply source can deliver and the impedance of the distribution system, they are limited on the secondary by the supply source and the impedance of the transformer.

I need to check this, but I am sure you do not need the neutral on the primary/input (208 VAC).

You really are not really back feeding/reverse feeding the transformer, you are supplying a transformer primary and obtaining a need distribution voltage on the secondary.


Nothing can deliver unlimited amps, we are limited by the source and what it can provide instantaneously during a fault.
 
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