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sorry, another dumb question

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  • sorry, another dumb question

    i know everyone is probably sick of noob or dumb easy questions so i apologize, but i heard this rumor somewhere, dont know where so here is my question.
    i have a welding table all build and stuff and my welder is grounded to the table(obviously) is it ok to set the welder on the grouded piece? or should i be keeping the welder away from the ground?
    thanks in advance for the help

  • #2
    Personally, I keep my equipment separate from the welding surface. mainly because if the "ground" cable (it should really be referred to as the work cable, because ground is relative to the situation) looses connection with the table, then the current could possible find another route back into your machine through the case. Zapping a couple hundred amps through circuits/components that aren't designed to handle it. Technically, it would probably vary from one machine to another, just depending on how it is designed and how isolated the welding circuits are from the rest of the machine. I just don't like to leave anything to chance when I have machines that start at $1K and are full of electronic controls. Similar case in point: A friend of mine borrowed my TIG to use as his house. My machine has a High Frequency starting circuit on it. His table also has a grinder mounted to it that has a grounded case. The case in turn is tied to the rest of the house through the plug and breaker panel. Every time he would start an arc, several electronic items in his house would reset. We finally traced it down to a corroded clamp on the earth ground. Effectively, the ground was not grounded and acted like a transmission antenna throughout the house. There are a lot of problems created by insufficiently grounded electrical systems than most people realize. That's why I try to isolate as much stuff as possible because stray electrical currents can find there way to some strange places...SSS

    Oh, BTW, the dumbest question is the one that is never asked. Everybody has to start from somewhere and the only way to get better is to ask what you don't know. I've been in and around welding for over ten years and there are still some simple things I probably should know, but just never ran across that particular situation some how.
    Last edited by SkidSteerSteve; 12-29-2006, 09:09 AM.
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    • #3
      Tigwelder06 welcome!!...I know that your welder is designed to handle a lot of different situations but the very fact that your asking is good and when I wonder if something is not right I usually follow my gut and don't do it. It would be like welding on the tailgate of a welding truck with the ground hooked to the tailgate. Instead the proper way would be to always hook the ground to the part and don't weld on the tailgate if you can help it. (seen a dude burn out every gauge on the dasboard of his truck that way once...and glad it wasn't me!)
      I see and sometimes do have the ground hooked to my workbench and weld something in a vise...that is sending all the load thru the vice's swiveling surface. That ain't right but sometimes you gotta do what you gotta do yuh know. Just don't go looking for it. What you are describing....if I'm getting you correctly...would be essentially the same thing as laying your part on top of your welder?? (I've done that too but only maybe a couple of times) Heck I've even welded the welder with itself!!

      Now before everyone on the board chimes in I just want to set the record straight here and say I've done about every wrong/not by the book thing in this regard when it was the only way to get paid that day but I do not have my ground cable hooked to the table at my production welding job or at shop or my mobile gig either ...I hook 'em to my work 95% of the time. Usually hook a vice grip to odd shaped objects and then the ground to that.
      And Ditto on all the stuff Skidsteersteve said!!

      So my official answer would be NO... you shouldn't do that
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      • #4
        Originally posted by TIGWelder06 View Post
        ... is it ok to set the welder on the grouded piece? or should i be keeping the welder away from the ground?
        As far as welding is concerned, if there is any level below beginner, that's where I am. So, I'm responding strictly to the electrical content of the question.

        If you have an ohmmeter handy, check the resistance from the work clamp to the the welder case. If you show an infinite or very high reading, you may be safe with the welder case sitting on the work table.

        Remember, welding is a high amperage but LOW voltage process. And, per Ohm's Law, Amps = Volts/Resistance, it's the voltage that determines how many amps can flow across the case/work resistance path. Even a CC machine that increases voltage to keep the current constant will max out at a relatively low voltage (<80 volts on my Thunderbolt XL).

        Now for the disclaimer: What I said is true only for constant, steady state DC voltage. If there is a capacitive connection between the work clamp and the welder body, an ohmmeter will show an infinite (DC) resistance but with AC or transient DC voltages, you could still have high transient current flows.

        So you MAY be safe. But, my recommendation is to electrically isolate the welder body from the work. If the convenience of the welder sitting on a shelf of the workbench is important to you, sit it on a piece of plywood, plexiglass, thin rubber sheet, or some similar insulating material. It won't take much, but it's better to be safe than to let Murphy's Law ruin your whole day.
        Tom Veatch
        Wichita, KS


        • #5
          I know from experience that the early XMT 304's couldn't handle being grounded to the work, I don't know about the latest equipment. I was doing some tig work at Kwantlen University College in Surrey Canada and they had three out of four of thier XMT units fry internally at different times from not being isolated from the work. The welding booths had convenient trays to hold the machines, and the trays were part of the frame work that had the tables upon which the welding was being done. After rubber mats were installed under the power sources and wire feeders, the problem went away.

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          Esab PCM 1000


          • #6
            hey guys thanks alot for the info it really helped