# X-former question



## Jimmay (Sep 25, 2009)

Today I installed a 277-120v transformer and had quite a time afterward.

Checking voltage after I had 125 across x1 and x3. Checked the receptacles and had 125v. The problem was that the 125 was on the neutral side. So common sense dictates that I switch leads on x1 and x3. checked voltage again and 125v across x1 and x3 but still the same results that the neutral line was hot. Measured x1 to grnd 26v and x3 to grnd 43v. No matter how I switched the leads the neutral was always hot. There was no load on the circuit except for a drop light that I plugged in. 

Can anyone explain this to me? I can use all the help you can give me. 

Thanks in advance 
Jimmay


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## Bob Badger (Apr 19, 2009)

Jimmay said:


> Today I installed a 277-120v transformer and had quite a time afterward.
> 
> Checking voltage after I had 125 across x1 and x3. Checked the receptacles and had 125v. The problem was that the 125 was on the neutral side. So common sense dictates that I switch leads on x1 and x3. checked voltage again and 125v across x1 and x3 but still the same results that the neutral line was hot. Measured x1 to grnd 26v and x3 to grnd 43v. No matter how I switched the leads the neutral was always hot. There was no load on the circuit except for a drop light that I plugged in.
> 
> ...



You have not bonded the secondary to ground.


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## Jimmay (Sep 25, 2009)

Which one do I bond to ground? 

I transferred the wires exactly how they were on the original xformer.

Then again maybe thats why it smoked!


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## raider1 (Jan 22, 2007)

Either one, it does not matter.

Without grounding and bonding the secondary of the transformer correctly, you can not trip an overcurrent device from a ground fault.

Chris


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## nitro71 (Sep 17, 2009)

I really don't recommend the willy nilly connection strategy. You really should know exactly why you are connecting each conductor to that transformer along with proper bonding and grounding. Your neutral and ground have to be bonded together in either the transformer or the first disconnect.


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## Southeast Power (Jan 18, 2009)

Jimmay said:


> Today I installed a 277-120v transformer and had quite a time afterward.
> 
> Checking voltage after I had 125 across x1 and x3. Checked the receptacles and had 125v. The problem was that the 125 was on the neutral side. So common sense dictates that I switch leads on x1 and x3. checked voltage again and 125v across x1 and x3 but still the same results that the neutral line was hot. Measured x1 to grnd 26v and x3 to grnd 43v. No matter how I switched the leads the neutral was always hot. There was no load on the circuit except for a drop light that I plugged in.
> 
> ...



Jimmay,

How did you decide that the neutral was hot?

What kind of transformer is it?

Can you send us a link or catalog #


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## wildleg (Apr 12, 2009)

Jim, are you an electrician ?


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## Loose Neutral (Jun 3, 2009)

Xo and that aint no kiss.


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## brian john (Mar 11, 2007)

If as the poster noted the XMFR is 277 to 120 I would think he has X1 and X3 typically they woould be tied together as would X2 and X4, then he could willy nilly bond either side to ground.

He would either have X1 and X2 or X1, X2, X3, X4


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## Jimmay (Sep 25, 2009)

The xfrmr is a FPE and the secondary has x1 x2 x3 x4. No X0.

wildleg, Yes I'm an electrician, I mainly do residential service work. I haven't worked with xfrmr's that much except doorbell xfrmr's. I asked the question because there is alot of knowledge here and I thought i would ask people more experienced in this area. If I wanted to get bashed or get in an arguement I would go home to the wife.

Jrannis, 
When I tied my conductors onto x1 and x3 I had 125v in the receptacle. but the neutral side had the 125v to grnd and 0v on the hot side to grnd. When I disconnected the conductors is when it read 26v on x1 and 43v on x3.

Nitro71,
The ground and neutral are bonded in the main panel that supplies the xfrmr but I guess that I need to do it elsewhere. But what I'm gathering is that I should jumper off of either x1 or x3 to the xfrmr box. The electricians that wired this place did not run ANY ground wires, they used the conduit as the ground. 

Brian John,
Are you saying that I should jumper x1 and x3, then jumper x2 and x4? Because the schematic shows x1 to x4 for 120. Then jumper my neutral conductor to grnd.


I really appreciate all of the responses. Thanks to all.


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## nolabama (Oct 3, 2007)

I am no transformer expert my a long shot but I think your gonna want to run an EGC first. Then I "think" (bad word with me sometimes) when you "willy nilly" bond as Brain John say's your problem will clear up. BTW Brian John is a transformer expert.


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## Jimmay (Sep 25, 2009)

My bad on the previous post.
The primary terminals are in order: H1, H2, H3, N/A
The secondary terminal are in order: X2, n/a, XF, X1

The cat # ff250xk

The original xfrmr had x1 x2 x3 x4.

sorry guys


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## brian john (Mar 11, 2007)

At the transformer with nothing connected you should have 120 VAC from X1 to X2.

If that is the case bond either side to ground it makes no difference. This should clear up your issue. DO NOT BOND THE SIDE WITH THE OCP (over current protection fuse or circuit breaker).

I searched FPE web site and could not locate that model for drawings.


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## Jimmay (Sep 25, 2009)

Thanks Brian! 
I will do it first thing in the morning! I really appreciate your help.


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## 480jc (Jan 8, 2010)

*transformer question*

I'm working on a single phase 480 system right now...hooking up a single phase 3kva xfrmer fed from a single phase breaker with 240 voltage and a neutral...the high side of the xfrmer tells me to connect h1 and h3 together and h2 and h4 together...so does this mean I bring my neutral to h2 and h4? and splice my hot to h1 and h3? I've never hooked up a neutral to the high side of a xfrmer before...
second question...load side...
I need 120 v and a neutral for the low side...diagram says 3 options, 240, 120, or 120/240...I only need 120...but I need a neutral...diagram says hook x1 and x3 together and x2 and x4 together...so my question is x1 and x3 will be my hot leg? and x2 and x4 will be my neutral?
thanks


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## micromind (Aug 11, 2007)

It doesn't matter whether the hot goes to H1-H3 or H2-H4. The hot goes to one, and the neutral goes to the other. The transformer only wants to see 240 volts, it doesn't care if one is hot and the other is neutral. 

For 120 only on the low side, X1 and X3 are spliced together to form one side of the 120. X2 and X4 are spliced to form the other side. One of these must be grounded. It doesn't matter which one. The grounded one is also the neutral. 

A 3 KVA single phase transformer will draw 12.5 amps from a 240 volt source, and it'll produce 25 amps at 120 volts. Read article 450 in the NEC to determine how to protect it. Pay particular attention to table 450.3(B).

Rob


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## zgozvrm (Jun 17, 2009)

480jc said:


> I'm working on a single phase 480 system right now...hooking up a single phase 3kva xfrmer fed from a single phase breaker with 240 voltage and a neutral...the high side of the xfrmer tells me to connect h1 and h3 together and h2 and h4 together...so does this mean I bring my neutral to h2 and h4? and splice my hot to h1 and h3? I've never hooked up a neutral to the high side of a xfrmer before...
> second question...load side...
> I need 120 v and a neutral for the low side...diagram says 3 options, 240, 120, or 120/240...I only need 120...but I need a neutral...diagram says hook x1 and x3 together and x2 and x4 together...so my question is x1 and x3 will be my hot leg? and x2 and x4 will be my neutral?
> thanks


It's not really clear what you're working with. First, you say you're working with a 480V single phase system, but then you state that you're connecting a transformer to a circuit breaker fed by 240V single phase.

It seems that you have a typical 240x480 - 120/240 single phase transformer. This transformer takes either 240V or 480V as it's primary voltage and gives you either 240V or 120V as it's secondary voltage. So you have 4 possibilities:
240V to 240V
240V to 120V
480V to 240V
480V to 120V

In the case of 240V to 240V, the transformer is acting as an isolation transformer.

I assume that your 240V is coming from one leg of your 480V and a neutral (so you have a center-tapped transformer feeding your 480V). If this is the case, I would use a 2-pole circuit breaker connected to 480V to feed your new transformer. That is, one leg of your 480V to one pole of your CB and the other leg (not neutral) to the other pole of your CB. Then, connect the load wires from the circuit breaker to H1 and H4 on your Xfmr and connect H2 and H3 together. To get 120V output, connect X1 and X3 together and X2 and X4 together. Tap off X1 and X4 to get your 120V. At this point, you will have 120V ungrounded (no neutral). If you want a neutral & ground, connect one leg (either X1 or X4) only to ground. This will become your neutral.

If you insist on using the 240V breaker as the primary voltage, first of all, be sure that the breaker is a single-pole breaker (you should not be switching the neutral). Then, connect load wire from the CB to H1 on the Xfmr and the neutral wire to H4 on the transformer. H1 should be connected to H3 and H2 should be connected to H4 (no connection between H2 and H3, as with the 480V set-up). The secondary connections remain the same.

Be sure to make all of your connections with the power off, leaving the primary connection for last.


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