# Wiring Diagram for a Transformer



## micromind (Mar 9, 2008)

The transformer connection shown is for 3 phase applications. It's called a buck-boost wye to wye. It uses 3 single phase transformers. For a single phase application, only one transformer is needed. The part number given is a square D 1KVA, 120/240 primary, 12/24 secondary. It can raise or lower voltage by either 12 or 24. The drawing shows 12. There must be a heck of a machine connected to it, because at a change of 12 volts the transformer is capable of driving an 83 amp load. 

Each of the H windings are connected phase to neutral (hence the wye connection) and will induce a voltage in the X windings. In order for power to get from the HV side to the LV side, it has to go through the X windings. In this case, the X windings will reduce the voltage. They can be re-connected to raise the voltage as well.

The single phase connection is a bit different, the secondary is the same, but the primary must be connected in series for 240 volts. 

As shown in the drawing, the H windings are 120 volt, and the X windings are 12 volt. Higher voltage = lower current, lower voltage = higher current. This explains the difference in wire size. 

Rob


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## XR72 (Aug 6, 2009)

Thanks Micromind.

The part that confused me was the chart saying only 1 transformer needed and then showing a diagram with 3 transformers on it. I thought mabey they were all somehow the same transformer in some odd arrangement of wires.

One more question though. What is that little symbol below the 2nd LV from the left? Is it a breaker?


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## Stubbie (Jan 7, 2007)

I agree with Rob. Your showing a 3 phase 4 wire source powering a 3 phase 4 wire load (wye to wye). As Rob points out the transformer is showing a parallel connection producing a 12 volt decrease but I'm questioning the drawing being the one you want. You are wanting to reduce 240 volt single phase to 218 volts or close to that I guess. 

I would also like to know what the machine is that your powering and its electrical requirements.


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## Stubbie (Jan 7, 2007)

XR72 said:


> Thanks Micromind.
> 
> The part that confused me was the chart saying only 1 transformer needed and then showing a diagram with 3 transformers on it. I thought mabey they were all somehow the same transformer in some odd arrangement of wires.
> 
> One more question though. What is that little symbol below the 2nd LV from the left? Is it a breaker?


Actually it should be the same as the one below the 3rd lv from the left. No it's not a breaker it is simply showing that there is no connection to the load hot wire (it just jumps over it) and goes on to the neutral. The drawing does have a mistake...that little connection to the load wire you see shouldn't be there. It should just jump over the load wire like the other one.


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## XR72 (Aug 6, 2009)

Found out I was reading the table wrong. I think it should have been this one.










We use a GBC 2080WFt Wide Format laminator.

The manual says:

Voltage: 220
Current: 11.3A
Power: 2500 W
Phase: Single

There's a board in the laminator that keeps dying. Its the same part every time, it just stops working and needs replacing.

The first two times it happened, the fuses were fine. Now, we can't even turn the machine on without blowing the fuse to that part.

The digital multimeter we used to test the line says its putting out 245 volts, so we think that's one reason. We are also in a manufacturing area where construction is not uncommon, and apparently that can effect the power coming in. Hell, a transformer on a pole outside even exploded a few weeks ago.

So we want to reduce the voltage closer to 220v. We probably have power spikes as well, but none of our other equipment seems bothered by it. Just the 2080WFt.


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## mpoulton (Jul 23, 2009)

XR72 said:


> The digital multimeter we used to test the line says its putting out 245 volts, so we think that's one reason. We are also in a manufacturing area where construction is not uncommon, and apparently that can effect the power coming in. Hell, a transformer on a pole outside even exploded a few weeks ago.
> 
> So we want to reduce the voltage closer to 220v. We probably have power spikes as well, but none of our other equipment seems bothered by it. Just the 2080WFt.


What is the nameplate voltage rating on the equipment? If it's 208, then the 245 you're giving it is definitely unacceptable. However, if it is 220, 230, or 240V then the power you are providing should be fine. 220, 230, and 240V are all really synonymous, and refer to a system which has a nominal supply voltage of 240V (these days). 245V is well within tolerances for a 240V system, and should be fine for equipment marked for use with 220-240V.


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## micromind (Mar 9, 2008)

Using 'wiring diagram 4', if the HV is 245, the LV will be 221. 

If the transformer is a Square D 1S43F, and it's connected per 'wiring diagram 4', the maximum load current will be 42 amps. 

This transformer will easily handle the machine it's intended to operate.

Rob

P.S. After you get the transformer connected, leave one wire disconnected from the machine. Make sure it's not touching anything. Turn it on. Be careful here, you'll be working with live (and lethal) voltages. Measure the output voltage. It'll be either around 221 or 269. If it's 269, swap X1 and X4.


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