I have had a newly bought cheapo Toncon inverter DC tig welder sitting around unused for around a year and have decided to get it up and running. All power outlets in my shed run through an old fashioned isolating transformer via a portable distribution box for the leads. The user manual appears to recommend earthing the body of the welder separate from whatever the power cord provides, and has an external stud on the body for this purpose. The plug on the machine's lead has the earth prong marked as such.
My question is: should I bypass the transformer, and do I need the external earthing? If so, what is the best way to achieve that?
I am not referring to the earth for the welding clamp.
ignition328,
Oct 8, 4:00pm
You don't necessarily have to long as the case goes to the ground pin of your outlet. You want to create a HF ground return path though and for that an isolated earth helps. I'd recommend proper grounding though on the basis of the noise they generate.
HF tig welders make a hell of a lot of noise on the line. If you're working out of something like a shipping container I'd ground that as well. Electronic equipment like computers or really any microcontroller HATE the noise that tigs generate. Depending on how good the power supplies of said equipment is you can cause shutdowns and damage to said equipment; there is some equipment I've made for operating in welding bays before and I had to isolate a tonne of stuff to make it work right, lots of ferrites and 470μH chokes. That goes for neighbours as well, I can pick up HF on some systems from nearby buildings hence grounding any large metal pieces in the weld area.
tweake,
Oct 8, 4:27pm
whats the rating of the welder? i doubt the distribution box or maybe even the transformer is going to handle it for long. have the power run through the least amount of connections and gear possible.
budgel,
Oct 8, 5:02pm
Thanks for the replies. I wont use the transformer when using the welder as it has a 16amp plug fitted. The welder has a rated input capacity of 4.6 KVA according to the spec sheet, and the mains voltage is 220v at 50/60 Hz. It is called a TIG 200. Oddly (perhaps) I have used my 150amp mig through the transformer, but have only welded thin stuff & never had it turned right up, so havent been caught short.
just reading the bit on the Workpiece Ground. if i read that right you connect your table or workpiece to the ground stud which in then is connected to the ground in the power lead.
budgel,
Oct 8, 5:57pm
I checked for continuity between the earth stub and the earth pin on the plug. Nothing! The external stub has continuity with the rest of the body/case of the welder, but the earth wire on the lead is connected to the large aluminium heatsink inside the welder and isolated from the rest of the machine. The electrical workings are mounted to the frame by about 10mm square plastic rods. I am wondering if this is legal. The welder is brand new and has never been plugged in since I bought it!
tweake,
Oct 8, 6:11pm
not 100% sure but i would have thought for basic safety if its got a metal outside case it should be connected to the earth pin.
supernova2,
Oct 8, 8:58pm
Perhaps it's factory double insulated. has it got the square inside a square symbol on the data plate?
msigg,
Oct 8, 9:57pm
The old fashioned isolating transformer has 0 potential to ground. So the earth will be doing nothing. That's the way I read it.
tony9,
Oct 8, 10:04pm
You should not use multiple appliances through an isolating transformer. If two or more become faulty they can cause electrocution, and you lose the basic earth protection available without a transformer.
Replace it with a portable RCD which can drive multiple appliances.
tegretol,
Oct 8, 11:50pm
Does the welder have any sort of NZS info on it and what does the supplied SDoc say about safety certification in NZ?
marte,
Oct 9, 1:05am
Is the casing supposed to be a earthed Faraday cage or something? It sounds like it.
TIGs don't use much power so the power supply will probably do anyway.
msigg,
Oct 9, 9:06am
As above tony9 or mccb on board he is correct.
budgel,
Dec 30, 12:52am
No double insulation marks or S Doc. These welders were sold widely on trademe, but have now been phased out. Mine may have been the last one sold. It is branded Toncon which is a reputable Chinese manufacturer, but there is no reference to the welder on any of its online media. A google search leads me to think it is a generic Chinese welder that could have any brand put on it. Yeah, I will replace the transformer with an RCD today, It has just been there for years without much thought going into it.
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