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  • welding table - ground?

    I'm working on an upgraded welding table. Since I often need to plug in angle grinders or other power tools, I plan to install some 117VAC outlets on the table, and plug them into the wall behind the table. I'm wondering about connecting the table to earth ground.

    In other words when I connect the welder's ground clamp to a part clamped on the table, that should be at earth potential, right?

    I know if this were a hi-fi I'd be generating a big fat ground loop, which would be bad design. It just seems weird to me to think about running conduit and jboxes and not grounding them. Of course, the outlets themselves will be grounded.

    metalmagpie

  • #2
    In reality.. use a steel outlet boxes correctly grounded to the incoming power cord and you are ready to go. For the currents you are concerned with, Conduit is a legal ground if installed correctly. Oh.. it's not legal to use metallic conduit unless it is grounded. The conduit is grounded via the j-boxes.

    If you are worried use a #6 wire with lug (typical nec "equipment ground') and ground the table to your ground spike.

    There is no issue with "ground loops". Ground in electrical distribution systems are multiple and redundant

    Don't assume you welder "ground" is really " ground" for electrical safety purposes. Any current from the welder will return via the welders ground return lead. Does your welder even work of you leave that clamp off but the work is "grounded". if so... run a FAT (sized to the welder) ground lead back to the panel, just incase you forget to clamp on the welder lead. Somehow I doubt it will work without the welder "ground" clamp on.
    Last edited by lakeside53; 08-18-2015, 11:23 AM.

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    • #3
      It probably wouldn't hurt but I found all the wire under your feet was a problem, so I got some recoil units mounted to the ceiling for 110v and air, keeps them out of the way, and if they are under your table you need to change the flex on the tool to heat resistant, I melted a few before I got the message
      Mark

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      • #4
        The welder's ground clamp is rightly called the "work" lead. It's purpose is to provide a return path for the welding current (from the stinger/gun). It is not the same as the 110v (or 220v) ground.

        I would NOT ground the table. I'd isolate the outlets from the table. Use the principle of "double insulated".

        My reasoning; If you ground the table, it becomes a very likely return path for any accidental contact with a live electrical wire. It's also very likely that you will be touching that table when you accidentally cut through the power cable on your grinder.

        Disclaimer: I have no idea what NEC says about grounding a welding table.

        Dan
        At the end of the project, there is a profound difference between spare parts and extra parts.

        Location: SF East Bay.

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        • #5
          I found this, which states that the welding table must be separately grounded:
          http://www.thefabricator.com/article...aying-grounded

          According to American National Standards Institute (ANSI) Z49.1, "Safety in Welding, Cutting and Allied Processes," the workpiece or the metal table that the workpiece rests on must be grounded. You must connect the workpiece or work table to a suitable ground, such as a metal building frame. The ground connection should be independent of or separate from the welding circuit connection.
          http://pauleschoen.com/pix/PM08_P76_P54.png
          Paul , P S Technology, Inc. and MrTibbs
          USA Maryland 21030

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          • #6
            As above to what they say, however the steelwork on buildings are often welded to and on, the electrical earth is connected to the steelwork, if however the 0volt of the welding set became detached I suppose there would be a risk of the earth leads of the tools becoming the 0 volt line, if you see what I mean, that would be bad!, so what they said applies!, my tools are not connected to the bench by the earth, I'm guessing that with the right circumstances the bench COULD end up at 240 volts also very bad, it would trip every breaker, the earth leakage trip etc over here but that's with our wiring
            Do the safe thing, I retract wouldn't hurt as bad
            Mark

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            • #7
              My welding table is ground........

              JL...............

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              • #8
                The welding return cable is not grounded.....

                So no issues with double grounding should exist. Ground the worktable and go on with life

                If your welder is from 1902, I have no idea how it is set up..... but any modern or reasonably modern welder is isolated, for reasons that are obvious as soon as you consider welding on structural steel, and what that would do ground-wise if there were a grounded return wire.
                1601

                Keep eye on ball.
                Hashim Khan

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                • #9
                  Originally posted by JoeLee View Post
                  My welding table is ground........

                  JL...............

                  That must be a " TIG ONLY" table, or the photo was taken moments after the table was placed in service. Even brazing flux leaves marks ;-)

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                  • #10
                    The output from a welder is isolated from the mains, so the ground lead is not at earth ground. The only connection to earth ground may be though a couple foil capacitors inside the welder to shunt away HF from getting into the machine.

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                    • #11
                      Originally posted by CalM View Post
                      That must be a " TIG ONLY" table, or the photo was taken moments after the table was placed in service. Even brazing flux leaves marks ;-)
                      Nah, he lays down cardboard prior to welding to keep that surface pristine.
                      Location: Long Island, N.Y.

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                      • #12
                        It's a J-B welding table

                        The output winding of the welder transformer should be well isolated from ground and the primary. The transformer in my cheap welder appears to be a "split bobbin" type which offers very good isolation at the expense of high leakage inductance and poor voltage regulation, but that's a desirable feature for welding because it limits the maximum current to a safe value. If the transformer is layer wound there may be considerable capacitance between primary and secondary which could provide enough current for a mild shock. If the table is not grounded, it presents a hazard if the operator touches earth ground with another part of the body.
                        http://pauleschoen.com/pix/PM08_P76_P54.png
                        Paul , P S Technology, Inc. and MrTibbs
                        USA Maryland 21030

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                        • #13
                          Originally posted by JoeLee View Post
                          My welding table is ground........

                          JL...............
                          and Blanchard ground at that!

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                          • #14
                            My guess is it started out as a 4" thick top and he likes to use his blanchard grinder.

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                            • #15
                              No, actually it started out as a 1 1/4" thick piece of plate, blanchard ground on each side with a finish dimension of just over 1 1/8" thick.
                              I made it back in like 2005 and the picture was taken last year. I mostly TIG, if I should MIG weld on it I have a piece of galvanized sheet that fits over it to protect it from splatter.

                              Now back to the subject............. I never ground to the table, intentionally anyway. There have been times when I've forgotten to ground my work and the clamp was clamped to the table, I'll usually find that out pretty quickly as I'll hear a snap when the part arc itself to the table to make it's connection.

                              I believe my Miller Synchrowave has floating ground. I've never checked it with a continuity meter to see if the ground wire is isolated from the electrical outlet ground. I assume it is. I have gotten RF bites on my arms if I should touch them on the table when I'm welding if I ground through the table.

                              JL.....................

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