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Old 08-29-2012, 03:44 PM   #1
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Adding a 480V Welder


Greetings,
I'm adding a 480V welder to my shop/out building, by reversing a 480P/240S transformer. Here's a picture of how the out building is currently wired and how I think the transformer and welder should be wired.



Any and all help/feedback is appreciated.

Thanks,
E

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Old 08-29-2012, 06:19 PM   #2
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Adding a 480V Welder


That looks decent, except for a couple minor things: First, the connection between the welder's work lead and the electrical system ground may not be a good idea. Many older welders do this, but most newer ones have an isolated output. The reason is that if the welder's work lead is bonded to the system ground and you are welding on something that is also grounded to the electrical system and the work clamp comes loose, the welding current will return through the grounding conductor. That almost inevitably melts the grounding conductor and may start a fire. Second, I see you have a 40A breaker feeding the transformer. Assuming you sized it correctly, that's not a very big welder. It would probably be cheaper and easier to get a 240V welder instead of using a transformer to provide 480V to a rather small welder.

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Old 08-29-2012, 08:24 PM   #3
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Adding a 480V Welder


Thanks for taking a look at the diagram and your feedback.

According to the welder's schematic, the output is isolated. Grounding the work electrode is straight from the owner's manual. Your "what if", concerning what would happen if the electrode connection opened up, is interesting. I'll have to chew on that a little bit. I plan on using a metal work table, so I certainly could bolt the electrode directly. Of course there'll be a seperate connection for the work table to safety ground.

You're right the 40A breakers are undersized for full load welding. I've run a 200A buzz box off it with no problems at low current settings. The 480V welder is a TIG unit. I use oxy-fuel for bigger stuff.

I plan on increasing to a 400A service in the near future and will likely bump up the barn's piece of it as well. The transformer is already sized for the full load of the welder.

I got the 480V welder for next to nothing and the transformer was $300. I'm way under the price of either a new or used welder of the same capability.

Thanks again,
Eric
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Old 08-29-2012, 09:14 PM   #4
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Adding a 480V Welder


After being in the business of heavy industrial welding for much of my working career, Single phase 480v machines are decidely rare, in fact, I have never seen one. Your diagram is showing single phase, is this correct?

Most machines have taps for smaller voltages, is there a reason you want to run 480v and not 240v?

Last edited by Anti-wingnut; 08-29-2012 at 09:19 PM.
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Old 08-29-2012, 09:34 PM   #5
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Adding a 480V Welder


Yes, single phase.

It's an older Econotig, which used different transformers for different input voltages. No taps. Swapping transformers was twice as expensive.
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Old 08-29-2012, 11:55 PM   #6
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Adding a 480V Welder


As long as the breaker and transformer are sized appropriately, it seems fine. For TIG work on an isolated bench the grounding of the work lead is not a problem. That's only a problem if the machine is going to be used to weld on structural steel or pieces of equipment that are also connected to the electrical system or other grounded metal.

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