transformer installation

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gary hoffman

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bellaire ,ohio usa
i am a residential electrician . i also have commercial experience. i own a building and i am installing a new elevator. the old elevator ran on 3 phase 3 wire 208, the new motor runs on 3 phase 4 wire 480, i need a step up transformer to achieve the necessary voltage .. the 208 is going to be on my primary side , the 480 volts will be on the secondary side... the elevator company said that ithey need 4 wires to feed their breaker for for the elevator. i am only feeding the step up transformer with 3 phase208 3wire how do i obtain the 4th wire on the secondary side?? the maximum load will be around 46 amps. i figure that a 1 kva transformer
rated at 100 amps will be enough.. can you please help me out???
 
You will need a 208v Delta to 480/277v Wye transformer and it it will probably need to be at least 45KVA. You will ground the XO terminal on the secondary side to make the fourth wire / Neutral.

I am not sure they really need a four wire feed but if that is what they are saying you should go with it.

Are you sure this won't need an engineers seal?

Roger
 
roger said:
I am not sure they really need a four wire feed but if that is what they are saying you should go with it.
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It is highly probable that the 'electronics' (e.g. VFDs and filters) need to have a grounded reference point, that does not exceed 300V line to ground.
 
gary hoffman said:
... i am only feeding the step up transformer with 3 phase208 3wire how do i obtain the 4th wire on the secondary side?? ...
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The 4th wire is a neutral, which is derived on the secondary just by the way the transformer windings are configured... i.e. one end of all three windings is connected together, while the other three ends are the hot legs. The neutral connection should be labeled H0. You will have to ground the neutral either at the transformer or secondary disconnect. See 250.28 and 250.30 regarding a System Bonding Jumper and Grounding a Seperately Derived System.
 
gary hoffman said:
the maximum load will be around 46 amps. i figure that a 1 kva transformer rated at 100 amps will be enough.. can you please help me out???
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I don't think you will be able to find a 1 kva at 100 amps. Better go with the 45 kva for safety.

As Conduiot said "How do you come up with a 1 kva transformer?"

Don't run off just because you got your answer. Come back an make your comments.
 
bob said:
I don't think you will be able to find a 1 kva at 100 amps. Better go with the 45 kva for safety.

As Conduiot said "How do you come up with a 1 kva transformer?"

Don't run off just because you got your answer. Come back an make your comments.
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If output voltage is 10 volts single phase or 5.77 volts three phase then you should have 1 kVA @ 100 amps;)



Need to determine what they mean by the "4th wire". Is it the equipment grounding conductor? Is it a 277 volt neutral? If so there is likely 277 volt loads somewhere in the supplied equipment.

I would be asking them why they can't supply a 208 volt unit, seems like it should be something fairly common.

But I don't mess with elevators, and in fact don't think I am qualified to even think about doing so either. The electrical inspectors here don't even look at them other than the main supply conductors, everything else elevator related is inspected by elevator inspectors and installed by people qualified to work on them.
 
As Roger indicated in post #4, you need a 208 delta/480 wye transformer. I would add that you also need to consider other issues/items such as a GES, disconnects, OCP, etc. You'll also want to consider the transformer sizing carefully depending on the type of elevator. I also would suggest some engineering help unless you are well versed in this type of situation.
 
kwired said:
If output voltage is 10 volts single phase or 5.77 volts three phase then you should have 1 kVA @ 100 amps;)
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Please explain how you come up with this. I know just enough about transformers to follow a wiring diagram for a buck/boost auto transformer!;)

Maybe...5.77V x 1.732 x 100A=999.36?
 
Little Bill said:
Please explain how you come up with this. I know just enough about transformers to follow a wiring diagram for a buck/boost auto transformer!;)

Maybe...5.77V x 1.732 x 100A=999.36?
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Well yes, but I did it the other way around

1000/100/1.732=5.773672055...

5.77 was the unknown being solved.
 
transformer specs...

transformer specs...

bob said:
I don't think you will be able to find a 1 kva at 100 amps. Better go with the 45 kva for safety.

As Conduiot said "How do you come up with a 1 kva transformer?"

Don't run off just because you got your answer. Come back an make your comments.
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the supply house did the calculation . i gave them all of the specs from the elevator company.
 
gary hoffman said:
i supplied the supply house with the specs for the elevator. they actually told me what was going to be needed.
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Well if they end up getting you a 1kVA transformer it will not cost all that much and will not be all that big, but it is not going to be able to handle the load either.

Might want to have that figure checked again. 1 kVA is only 2.77 amps @ 208V 3 phase or 1.2 amps @ 480V 3 phase.
 
Gary, it probably isn't the best idea to let sales people do electrical calculations and designs. I will ask again, are you sure this won't need an engneer to be involved? All the states I work in have very stringent rules governing elevators.

Roger
 
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