# Single Phase 480V Transformer Grounding Question



## Badboy_Matt

I'm a little confused by the this one.. And I want to see if anyone is in agreement with how I'm doing this or if there was a better way.

I have a 440 volt single phase spot welding machine that is being fed from an old Federal pacific transformer. The whole set-up is bolted to a custom permanent steel pallet. 








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The only panel I have access to in this area of the building is a 200 amp single phase panel. So I believe I should be wiring the transformer following the 240/120 connections. So it looks like the neutral should be connected to X2. 








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Below is how I have it wired now.. still need one more connector for the neutral.








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Before I energize does anyone think I should be using a different wiring method? 

Also what should I do about grounding the welding machine on the 480 volt side? Should I not do any extra steps since the entire unit is permanently bolted together on the steel pallet??

Any advice would be appreciated, I've been out of the electrical trade for a long time now all the transformer and industrial stuff is a bit confusing to me. Plus I want it to be connected safe for me and my guys. 


Thanks


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## RePhase277

There won't be a neutral on the 240 volt side. The midpoint at X2-X3 doesn't connect to anything.

Grounding the 480 volt side, you can ground the midpoint at H4-H5, giving you 240 volts to ground on each lead. Or you can ground one of the output leads, giving you 480 volts to ground.

Both primary and secondary grounds need to connect to the transformer case, and you need a grounding electrode conductor sized to the secondary OCPD.


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## Drew 64

Why do you think you need a neutral connection ?


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## Badboy_Matt

That makes sense thank you guys.

How would I ground the between 4 and 5? Or does it look easier to ground the output lead? The out put leads would be H1 and H2 so all I would have to do is put a ground to one of them, I guess?

Does the bent piece of copper on the left hand side inside the transform take care of my case connection for both my primary and secondary? 


I probably shouldn't say _NEUTRAL_ I should say grounded conductor.. But since this is being fed from a single phase panel where the phases are 180 degrees apart I thought neutral was a better way to describe what I've got going on here. I guess that doesn't matter.


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## RePhase277

Neutral is the right term for what you described, but you just don't need one here. From your primary feed, you'll have two hots and a ground. The ground connects nowhere but the case of the transformer.

The copper strap on the left just bonds the steel core to the case. To ground the secondary at the midpoint, you would connect onto the taps up top. It would likely be easier to just ground one lead, H1 or H2. In that case, you can't have a fuse in the grounded lead. A double pole circuit breaker would be OK, but no fuse.


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## Badboy_Matt

Hey big thanks to you RePhase277!!
I don't think I would have ever figured that out properly. Thank you for sharing your knowledge!


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## tommydh

Just my 2 cents 1 have you energized yet? I never rely soley on the factory strap and usually install a lug inside the transformer that in can pas the ground through stripping where it is under lug and terminating on frame or x0 when needed. If you are going from 240 to 480 you may need larger primary conductors to provide he correct amperage to operate the welder. Generally you step down so smaller primaries however its the opposite when stepping up.


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## tommydh

Is the steel pallet permant in place or portable by fork lift? If portable I suggest a seperate ground cable from any solid point on the assembly that can be connected to a nearby beam or other building steel. It can be a piece of 2/0 welding cable with clamp on it to hook up at location of use and removed when complete. If permanent you should run a wire tpo closest building steel


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## Southeast Power

I just noticed the presence of a couple of disconnects on that machine pallet along with a small control panel.
I can't think of any compelling reason someone would have removed the transformer terminations.
With that said, you want to make certian of a couple of things.
First. Did the previous installation have a secondary leg connected to ground inside of the disconnect?
Does the control need any of the low voltage 120/240 primary to operate or is it all 480.
I would check for any continuity between the secondary/480 side of the transformer before energizing it.
Also, I would test it energized before connecting a secondary phase to ground.
If you find 0 to ground on both phases, you can then decide on your secondary to ground scheme or possibly a ground detector.


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## Southeast Power

I dont think we have the entire story here.
Im suspicious of the whole setup and personally, bolt that beast to the floor if it were at all an option, and hard wire it. 
First we see the transformer connected for 120 volt on the low side and then we see the next pic with the transformer connected for 240.
I do see a pump control and some valve accessories on the machine.

I would be on nuclear hold until the operating voltage of every item on that machine was identified and traced back to its supply.

My first thought like others here might be that it's a somewhat uncommon setup and should be completely investigated.
Also, I see that you are cord connecting it with a straight blade. Although perfectly legal we usually see those burn on one side when they operate close to capacity and will normally choose a twist lock.

Is there any possibility the building side was 480 volt at its previous home?


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## Corysan

It looks like the disconnect switch is part of the welder. The sticker on the switch say 220V single phase. 



> Does the control need any of the low voltage 120/240 primary to operate or is it all 480.
> I would check for any continuity between the secondary/480 side of the transformer before energizing it.


I would open the control panel and look for a nameplate to verify voltage requirements. If it doesn't have a nameplate don't be surprised. If it doesn't need 120V or 240V control power, it will have some kind of control transformer or power supply inside. You may have to look really closely at the components. 

I would clean the transformer thoroughly first. Next I would check for bad continuity, primary to secondary should be OL, primary to ground (all terminals) should be OL, secondary to ground (all terminals) should be OL. If it passes, I would definitely megger each terminal to ground and then primary to secondary. Be extremely careful doing this! The transformer case should be connected to your grounding system for this test. After every reading, you must dissipate the built up charge to ground. The megger will provide a high enough voltage to shock you, and the transformer could step that up accordingly. 1000 volts applied to the low voltage side will yield 2000 volts on the high side. That said, your readings should be at least 1 Megohmm for 3minutes. That's not official, but it works.

This link might be helpful. See pages 28 and 29. http://www.iemworldwide.com/pdf/ansi-neta-mts-2011.pdf

Also, I would contact the sales company for assistance and documentation: Stanco Welder and Machine 847-635-4030

Good luck


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## Badboy_Matt

Thank you guys, yes those are all great suggestions.
I did get it powered up. I ended up connecting the transformer as seen in the last picture with my blue labels. I left the neutral on the x2 location and also ran a second ground wire from there into the welder case. 
This whole set up is a retro fit that was built by Stanco Welder and Machinery Co. I purchased it used but was able to find out the welder itself was made in 1983 and the Unitrol control unit was made in 2008. I really like what they did with it. The big custom steel pallet is great for moving it around and permanently marrying the whole setup together. I'm 99 percent sure the company before me had it running 220 single phase based on the label n the disconnect, the original wiring of the trans and the size 100 amp fuses in the disconnect. It needs 440 to power the welders primary transformer. This older unit was a 440 primary only. Yes actually the big white control panel is 240 volts so it gets stepped back down. Inside there is another small transformer which I did not have to mess with at all. 

I will be adding the 2/0 welding cable to the building frame as an extra precaution.


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## RePhase277

Badboy_Matt said:


> Thank you guys, yes those are all great suggestions.
> I did get it powered up. I ended up connecting the transformer as seen in the last picture with my blue labels. I left the neutral on the x2 location and also ran a second ground wire from there into the welder case.


What? Why? Now you've introduced a potential hazard. With it setup this way, you effectively have two 120 volt transformers using the ground as a neutral.

The proper way to connect this was said earlier. The only place the primary side ground needs to connect to is the transformer case. The X2-X3 link doesn't connect to anything. You are going to get someone lit up the way it is.


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## glen1971

RePhase277 said:


> What? Why? Now you've introduced a potential hazard. With it setup this way, you effectively have two 120 volt transformers using the ground as a neutral.
> 
> The proper way to connect this was said earlier. The only place the primary side ground needs to connect to is the transformer case. The X2-X3 link doesn't connect to anything. You are going to get someone lit up the way it is.


The diagram on the transformer even said so too! Connect X2 and X3, wires on X1 and X4! And your posts #2 and #5 spelled it out... Maybe this one will make one of MechanicalDVR's posts on "Gems of the Trade"?


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## telsa

If the prior voltage was 220 VAC then the hot side taps would be H1&8; H2&9.

Is that evident ?

Look at the table: 217 VAC, tap connections, at the bottom of the stack.


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## Southeast Power

We tried but, hey, IT WORKS!

I didn't think the OP understood that if the transformer input was 480, he could set it up two ways. One way would be straight 240, the other way, if a neutral was needed, he could install that jumper bar and tap between them.


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## glen1971

telsa said:


> If the prior voltage was 220 VAC then the hot side taps would be H1&8; H2&9.
> 
> Is that evident ?
> 
> Look at the table: 217 VAC, tap connections, at the bottom of the stack.


From the OP, it sounds like this is a step-up transformer for their "440 volt single phase spot welding machine".
From the pics, it looks like it may have been set up originally with 120 vac input. The pic below the transformer label shows X2 and X4 connected and X1 and X3. When the OP moved the Low Side jumpers to X2 and X3 connected, it is now set up for 240 vac input.. The OP has wired a neutral to their X2/X3 connection, which it is not required...

Unless I misread and am way out in left field....


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## Southeast Power

glen1971 said:


> From the OP, it sounds like this is a step-up transformer for their "440 volt single phase spot welding machine".
> From the pics, it looks like it may have been set up originally with 120 vac input. The pic below the transformer label shows X2 and X4 connected and X1 and X3. When the OP moved the Low Side jumpers to X2 and X3 connected, it is now set up for 240 vac input.. The OP has wired a neutral to their X2/X3 connection, which it is not required...
> 
> Unless I misread and am way out in left field....


I was looking at that thinking how nice it would be bringing 120 volts at 100 amps to that beast.


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## Badboy_Matt

I'm not trying to do the wrong thing here, maybe I'm not explaining something correctly here or understanding it properly.

The way I'm understanding it is the transformer's job here is to step up 240 single phase to 480 single phase.

*The leads on X1 and X4 are the incoming 240 volts. 
*X2 and X3 are jumpered together as shown on the transformer nameplate, it tells me to connect them together for the 240 volt and the 240/120 wire methods. 
*H1 and H2 are 480 going into the welder

I don't have it pictured but the X2 lead where the neutral is landed is a splice point and I just ran it into the welder. This is to ground the secondary side. I thought the primary 240 side did not need a ground since the everything is bolted together on one piece of steel making it one unit. 

Sorry if I'm still not understanding this or explaining it properly.


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## RePhase277

Badboy_Matt said:


> I'm not trying to do the wrong thing here, maybe I'm not explaining something correctly here or understanding it properly.
> 
> The way I'm understanding it is the transformer's job here is to step up 240 single phase to 480 single phase.
> 
> *The leads on X1 and X4 are the incoming 240 volts.
> *X2 and X3 are jumpered together as shown on the transformer nameplate, it tells me to connect them together for the 240 volt and the 240/120 wire methods.
> *H1 and H2 are 480 going into the welder
> 
> I don't have it pictured but the X2 lead where the neutral is landed is a splice point and I just ran it into the welder. This is to ground the secondary side. I thought the primary 240 side did not need a ground since the everything is bolted together on one piece of steel making it one unit.
> 
> Sorry if I'm still not understanding this or explaining it properly.


The primary circuit needs to ground the machine incase of a fault on the 240 volt side. That ground only connects to the case of the transformer. Connecting it to the X2-X3 bridge allows for the potential to energize the frame. The secondary side is grounded by grounding one of the H leads.


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## Badboy_Matt

RePhase277 said:


> The primary circuit needs to ground the machine incase of a fault on the 240 volt side. That ground only connects to the case of the transformer. Connecting it to the X2-X3 bridge allows for the potential to energize the frame. The secondary side is grounded by grounding one of the H leads.


I hear you, thanks for your patience. The reason I did not initially follow your advice was because I was told by a worker at the electrical supply house that I definitely do not want to hook up the high voltage lead anywhere besides the terminals they go to and I must keep them separate. 

Is there some other way to explain it so I can understand the flow of the possible fault current? I just don't understand how connecting one of the high voltage leads to the transformer case will help. I do now the original manual for the welder states the case of the welder must be grounded which I have done. Is is more like I need multiple ground connections because if someone is touching the case of the welder they will be a better path vs if they are touching the welder? 

But I do now see how the 240 side isn't connected properly. I will post new pics tomorrow.


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## RePhase277

Badboy_Matt said:


> I hear you, thanks for your patience. The reason I did not initially follow your advice was because I was told by a worker at the electrical supply house that I definitely do not want to hook up the high voltage lead anywhere besides the terminals they go to and I must keep them separate.
> 
> Is there some other way to explain it so I can understand the flow of the possible fault current? I just don't understand how connecting one of the high voltage leads to the transformer case will help. I do now the original manual for the welder states the case of the welder must be grounded which I have done. Is is more like I need multiple ground connections because if someone is touching the case of the welder they will be a better path vs if they are touching the welder?
> 
> But I do now see how the 240 side isn't connected properly. I will post new pics tomorrow.


On the 240 volt side, fault current will flow from a primary hot to the case and back to the service neutral on the green ground wire. But the secondary is generated with no electrical connection to the primary so there is no complete circuit for a fault to flow through unless you make one of the high voltage leads grounded.

Never listen to the guy at the supply house.


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