# 120/ 208v to 480v Equation for Amp ? Help



## Amelco (Feb 5, 2012)

So I have to take a 120/ 208 v wye at 200amps and convert it through a transformer to get 480v Delta. How many Amps will I have avaible on the 480 side when it goes through the conversion? I forget the equation.

I am powering an Elevator again and all I got to feed them is 120v at 200amps ( Temp Panel) and I am going put a transformer in and bump it to 480v. Hoping I got enough juice in amps on the other side.


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## freeagnt54 (Aug 6, 2008)

Amelco said:


> So I have to take a 120/ 208 v wye at 200amps and convert it through a transformer to get 480v Delta. How many Amps will I have avaible on the 480 side when it goes through the conversion? I forget the equation.
> 
> I am powering an Elevator again and all I got to feed them is 120v at 200amps ( Temp Panel) and I am going put a transformer in and bump it to 480v. Hoping I got enough juice in amps on the other side.


I got 50 amps on the secondary


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## McClary’s Electrical (Feb 21, 2009)

Amelco said:


> I am powering an Elevator again and all I got to feed them is 120v at 200amps .


 


So you're gonna be able to find a single pole 200 amp breaker?


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## Amelco (Feb 5, 2012)

What equation did you use
It is 3 phase everything? Hence a 120/208 wye and a 480 Delta.
Really looking for the equation in case I got to give more juice.


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## freeagnt54 (Aug 6, 2008)

208v x 200a = 41600va

Kva/(voltage·1.732)

41600/(480·1.732)
41600/831.36
=50.03amps


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## wildleg (Apr 12, 2009)

there's something wrong with this thread, and it's not just the math error above


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## freeagnt54 (Aug 6, 2008)

My mistake

208v x 200a x 1.732 = 72051va

72051/ (480 x 1.732) =86.6amps on the secondary


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## micromind (Aug 11, 2007)

wildleg said:


> there's something wrong with this thread, and it's not just the math error above


Yes indeed!

Is the source 120V single phase, or 120/208 3ø?

There's a huge difference, plus if the elevator is 3ø it cannot be powered by a single phase source feeding a 3ø transformer.

BTW, a 75KVA 3ø transformer with one side 480∆ and the other side 120/208 wye will have a 480 current of 90.2 amps and a 120/208 current of 208 amps at full load.


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## JRaef (Mar 23, 2009)

Everything is relative, no need to over complicate it.

208/480= .433, x 200A = 86.67A


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## frenchelectrican (Mar 15, 2007)

JRaef said:


> Everything is relative, no need to over complicate it.
> 
> 208/480= .433, x 200A = 86.67A


I going have to remember your shortcut on that.

Merci,
Marc


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## Amelco (Feb 5, 2012)

Sorry, I was typing on my phone. The source is 120/208 3 phase into backward wires transformer, kicking out 480 Delta 3 phase into an 80 year old Elevator. I appreciate the help.


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## brian john (Mar 11, 2007)

Amelco said:


> Sorry, I was typing on my phone. The source is 120/208 3 phase into backward wires transformer, kicking out 480 Delta 3 phase into an 80 year old Elevator. I appreciate the help.


You do not need 208/120 at the transformer, 208 wye to 480 delta, if there is a factory bond on the neutral/XO remove the bond jumper.


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## frenchelectrican (Mar 15, 2007)

brian john said:


> You do not need 208/120 at the transformer, 208 wye to 480 delta, if there is a factory bond on the neutral/XO remove the bond jumper.


 
Amelco.,

One thing you have to remember when you run the transfomer in reverse manner the main thing you have to remove the XO bond as Brian John posted.

Second thing is the inrush current you may run into the issue when you try to engerized with standard 200 amp breaker some case it may not hold it very well so just prepare to change the breaker or worst case change to smaller transfomer if the load can support it ( if the panel is rated to take larger breaker then you can do it )

Merci,
Marc


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## nitro71 (Sep 17, 2009)

On the primary side you would not use XO but on the secondary he is going to have to bond one leg to ground. Just so the OP understands that.


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## brian john (Mar 11, 2007)

nitro71 said:


> On the primary side you would not use XO but on the secondary he is going to have to bond one leg to ground. Just so the OP understands that.


Which is why I believe, especially as the OP's experience seems somewhat limited in this aspect of the trade. Go with a 208 delta to 480/277 wye.


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## BBQ (Nov 16, 2010)

brian john said:


> Go with a 208 delta to 480/277 wye.


Brain, obviously that would be great, but is impractical. 

This is for a temp feed and I will bet he has a 480 delta - 208Y/120 transformer available for use while the one you suggest would have to be purchased. 

If the OP can hook up a delta / Wye properly I am sure he could also hook up a back fed delta Wye properly given some brief direction from us.

As was pointed out

1) Do not land anything on XO

2) On the 480 side you have a couple of choices, one is installing ground fault indicators, the other more practical choice is corner grounding the delta output of the transformer. Pick a phase and ground it, that will now be a grounded conductor and should be white. 

You will still have 480 line to line but now you will have 0 to ground on one leg and 480 to ground on the other two legs.

Keep in mind you will not have a neutral and will not be able to get any 277 from this set up.


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## wildleg (Apr 12, 2009)

like I said before, there is something wrong with this thread.

the op has yet to state how much power is needed to run the elevator. you need to know how much power you need before you can figure out where to get it from. I haven't touched an elevator in recent memory that didn't take 100A 480 3p, and you guys seem to be fixing him up for a big fail. fail + 80 yr old elev = bigger fail.


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## nitro71 (Sep 17, 2009)

wildleg said:


> like I said before, there is something wrong with this thread.
> 
> the op has yet to state how much power is needed to run the elevator. you need to know how much power you need before you can figure out where to get it from. I haven't touched an elevator in recent memory that didn't take 100A 480 3p, and you guys seem to be fixing him up for a big fail. fail + 80 yr old elev = bigger fail.


I don't see it as anyone fixing him up for anything. He's the one calling the shots and in the end is the responsible party.


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## BBQ (Nov 16, 2010)

It has been shown already that he is limited to 80 amps of 480 from a 208 service, not including losses and other loads.

I would hope the OP would be able to put together that 80 amps of 480 is going to be an issue if the elevator needs 100 of 480.


More guys with negative waves, think positive.:laughing:


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## brian john (Mar 11, 2007)

wildleg said:


> like I said before, there is something wrong with this thread.
> 
> the op has yet to state how much power is needed to run the elevator. you need to know how much power you need before you can figure out where to get it from. I haven't touched an elevator in recent memory that didn't take 100A 480 3p, and you guys seem to be fixing him up for a big fail. fail + 80 yr old elev = bigger fail.



Most elevators we/I see and I see the distribution to elevators every week in IR reports and on job sites utilize a 480 VAC 100 AMP FSS or CB.


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## BBQ (Nov 16, 2010)

So lets see if got Brian position straight based on his posts and thanks

The OP is over his head to backfeed a transformer but is fine to use another kind of transformer in the more conventional way.

But the OP is over his head as far as load calculations even though others have pointed out how much KW he has available.

I thought the purpose of the forum was to help each other out, not find reason not to.


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## BBQ (Nov 16, 2010)

brian john said:


> Most elevators we/I see and I see the distribution to elevators every week in IR reports and on job sites utilize a 480 VAC 100 AMP FSS or CB.


Many do, some 150s, and some 60s. And as you know the breaker size has absolutely nothing to do with what they really draw.

The capacity, speed and type of elevator have everything to do with it.



Again, this is a temp, life is not perfect when feeding things temp.

Are we here to help or or not?


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## brian john (Mar 11, 2007)

BBQ said:


> So lets see if got Brian position straight based on his posts and thanks
> 
> The OP is over his head to backfeed a transformer but is fine to use another kind of transformer in the more conventional way.
> 
> ...



Bob,

I base my response of using a Delta to Wye transformer on my experience with electrical contractors that do what the OP is doing and then freak out with the voltages they get or leave the system ungrounded or ask how to get a neutral for their lighting.

Purely a suggestion based on experience, and not a requirement. 

We are here to help out and my suggestion was a proper response based on my experience and beliefs.


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## wildleg (Apr 12, 2009)

BBQ said:


> Many do, some 150s, and some 60s. And as you know the breaker size has absolutely nothing to do with what they really draw.
> 
> The capacity, speed and type of elevator have everything to do with it.
> 
> ...


you, of anyone, is here to shut people down when they are DIYing. you are therefore more qualified than anyone to answer your own question. Of course we are here to help out. How many red flags does it take, though ? (I'm not gonna say another word)


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## nitro71 (Sep 17, 2009)

The other way to look at this is: Would I want to ride in this elevator? Hell no, and I'll sue the crap outa anyone involved if something goes wrong with me in it.


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## brian john (Mar 11, 2007)

nitro71 said:


> The other way to look at this is: Would I want to ride in this elevator? Hell no, and I'll sue the crap outa anyone involved if something goes wrong with me in it.


Depending on the use, I know here there are multiple several inspectors that will look at the installation, plus the elevator companies are fairly involved with supply power to their equipment. If they see A-GND 480, B-GND 480, and C-GND 0, they might throw a wrench in the whole works, With ground alarms, they would see weird voltages to ground and possibly do the same.


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## stuiec (Sep 25, 2010)

nitro71 said:


> The other way to look at this is: Would I want to ride in this elevator? Hell no, and I'll *sue the crap* outa anyone involved if something goes wrong with me in it.


Pretty sure the OP just needs to ensure it is also listed as "death box" and he is good to go:thumbsup:


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## nitro71 (Sep 17, 2009)

stuiec said:


> Pretty sure the OP just needs to ensure it is also listed as "death box" and he is good to go:thumbsup:


 
:thumbup:


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## nitro71 (Sep 17, 2009)

That one line from Starwars comes to mind. "This isn't like flying a crop duster boy". I agree the OP seems deficient in to many areas to safely do this install. But not really up to us to figure that out.


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## brian john (Mar 11, 2007)

nitro71 said:


> That one line from Starwars comes to mind. "This isn't like flying a crop duster boy". I agree the OP seems deficient in to many areas to safely do this install. But not really up to us to figure that out.


And if he ask the right questions he will learn by doing.

Just coming here or at the other forums he will get a wide variety of responses, he needs to weed out the good from the bad and make a decision.


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## Amelco (Feb 5, 2012)

First. A Corner Grounded Delta is a UL approved system in the Code book.So is wiring a 480 Transformer backwards. Reason I am using the 480 transformer because they are readily avaible from my shops yard.
I could go buy the proper 120 to 480 transformer, but that GC would have to eat the 10,000 for the transfrmer.
Also, this temp power is for the Elevator guy to build his car, not run passengers.
The Elevtor does call for 100 amps at 480, then fused down to the Elevators guy request which should be around 70 amps. So I think 86 can get him buy till , permant power is installed for State Elevator inspection.


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## Amelco (Feb 5, 2012)

Done. Elevator is up and running


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## brian john (Mar 11, 2007)

Amelco said:


> First. A Corner Grounded Delta is a UL approved system in the Code book.So is wiring a 480 Transformer backwards. Reason I am using the 480 transformer because they are readily avaible from my shops yard.
> I could go buy the proper 120 to 480 transformer, but that GC would have to eat the 10,000 for the transfrmer.
> Also, this temp power is for the Elevator guy to build his car, not run passengers.
> The Elevtor does call for 100 amps at 480, then fused down to the Elevators guy request which should be around 70 amps. So I think 86 can get him buy till , permant power is installed for State Elevator inspection.


At what point did anyone say it was not NEC compliant?

Then you say you could buy the PROPER transformer?????????


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## Amelco (Feb 5, 2012)

Never. Running a trans backwards is UL complaint. So is a Corner ground.


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## Amelco (Feb 5, 2012)

$ 3,000 for the right Trans or aviable parts from supply yard, at no cost. Getting the 480 up the building will be a priorty to get my skid out of there.


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