Any american (or Uk I suppose) electricians able to give me some advice?

I am wanting to use a tig welder in a US house. The dryer outlet is on a 30 AMP breaker but the recepticle is an oddball 3 pin connection which supplies 2 hot 120 VAC pins and a neutral

the welder nees the 2 120 VAC pins and a ground

I am saying that it is not safe to wire the welder ground to neutral and some people I have spoken to are saying that it is safe.

Any ideas

[Edited on 8/11/07 by liam.mccaffrey]

I was under the impression that US wiring has the earth ("neutral" ) from the centre point of the generation transformer.
This would mean that the voltage between "hot" wires was 120v and from the "hot" wires to "neutral" is about 60v ?
In the UK we earth one of our hot wires to create and earth.
Can you test these with a volt meter and post what voltages you get?
I would need to know the voltage between the "hot" wires and also between "hot" wires and your "neutral"

[Edited on 8/11/2007 by nitram38]

yeah i can do that, once i get a voltmeter
I left all my gear back home

Where are you in the US?

--Chris

oklahoma, cushing

Doesn't it just plug in? Some older stuff had only two pins, but we usually have 3 now in newer places. If there are two, one of them is a bit wider. It's like this all over North America. I never understood why your plugs in the UK were the size of a small car.

not that straightforward unfortunately

why the dryer outlet and not just a wall plug?

because all the wall plugs are 120V and on 15AMP breakers

the dryewr outlet is 240V and on a 30 AMP breaker

Try wiring live to one hot pin, neutral to the other and earth to ground connection. This will work for things with transformers like most welders. If you are worried try metering for resistance between earth and neutral if you have a resistance here then it won't work.

If you have a two leg supply in your house then you could wire up a bunch of 13A 240 sockets to run all your UK stuff, just make very sure that the ground connection in the house is good as they work on 110V they aren't as careful as we are about getting a good earth connection!

Caber

Before you connect anything, do the voltage checks first!
If you use an earth as a neutral it will work, but if you should have a problem with an earth connection, you could find yourself with anything else that was earthed now being live. This could include the pipework in your house!

What you are describing sounds like a 2 phase supply. As you say one is neutral and the other 2 will be out of phase live giving 240v between them. In order to get your 240v for your welder you'll need to connect the welders neutral to one live and the live to the other live.

Unless the equipment is designed for a 2 phase supply bad things could happen to the electronics. Getting a step up transformer would be a better plan.

Bear in mind the US use 60Hz and we use 50Hz which can screw up some electronics.

That is why you should start with a voltmeter to determine what is going on first before you plug anything in!

There are 2 types of 240V recepticals in the US, one is a 3 wire which has 2 120V live feeds (red and Black) and one neutral (white) which also acts as a ground, in these cases the appliance will have a grounding strap from the frame to the center neutral return wire. The other type is a 4 wire which has an additional ground wire so the grounding strap on the appliance is not needed as the frame of the appliance is directly grounded to the receptical. Using a 3 wire 240V supply with an appliance that is not designed for it (no grounding strap) would be dangerous. Better to use a Step Up Transformer

I don't see how you could measure resistance between neutral and earth. The neutral can float several (often tens) of volts above earth. People used to ring their doorbells by connecting between earth and Neutral.

So sticking a meter on Ohms range between Earth and Neutral would probably give you a bent needle.

Best approach would be measure ac volts between the two Lives. and between the two Lives and the neutral. If you get 220V between the two lives you could connect your unit Live to live 1 and Neutral to live 2 as suggested above.

I would then connect your unit earth to an earth spike in the ground (safest cos you'll be standing on it) or to the domestic earth connection.

Most USA homes have two phases and neutral for supply. You should find 220 nominal volts between phases, and 110 nominal between phase and neutral.

Most usa water heaters,cookers, washers, dryers and heavvy draw houshold aplianses run on 220 volts.

Cheers,
Nev.

quote:

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Originally posted by liam.mccaffrey
oklahoma, cushing

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watch out with the freq. difference!

everything wich has some timeing in it will be way of or not survive the plugin.

a microwave could end up doing the 1 min in less seconds etc. etc.

Tks

appreciate your input fellas

Keith Weiland and Neville Jones have it right we have a 3 wire 120/120/Neutral supply giving 240 between phases. I have spoken to a sparky, who happened to also be a welder, he said it is perfectly safe to connect my welders ground to the recepticle neutral, and has done it on many occasions himself with no problems. He also explained to me exactly how to make an appropriately spec'd adapter cable.

Just to clear up any confusion, Im not trying to use UK equipment on US supply. Its US equipment designed to be run on 240V

Nitram; I'm still gonna check the voltage on the pins though

Liam,

You should have said it was a US welder in the first place. It should already have the proper grounding straps if its designed for 240V but I would have expected it to also already have the right type of plug.