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Old 02-11-2017, 01:13 PM   #1
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Default Single Phase 480V Transformer Grounding Question

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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Old 02-11-2017, 01:24 PM   #2
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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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Old 02-11-2017, 01:29 PM   #3
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Why do you think you need a neutral connection ?
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Old 02-11-2017, 02:02 PM   #4
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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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Old 02-11-2017, 02:16 PM   #5
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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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Old 02-12-2017, 08:22 PM   #6
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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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