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  1. #1
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    Welder Ground Lead

    This is a common on new construction buildings where the welders are all connected to a panel in an area and they only run one lead to the location where they're welding. The other lead goes to the nearest electrical conduit, metal strut, and anything else that's connected to the building electrical system. We recently had a problem with a large MC feeder that was arcing against some EMT due to this. How dangerous is this practice of grounding one side of the welder to electrical raceways?

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    Rob

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    All responses based on the 2014 NEC unless otherwise noted

  2. #2
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    Quote Originally Posted by infinity View Post
    ...We recently had a problem with a large MC feeder that was arcing against some EMT due to this. How dangerous is this practice of grounding one side of the welder to electrical raceways?
    Can you provide more information has to how this feeder arcing was determined to be "due to" the welders? I've never heard of that, and I've been welding for 30 years and am a long-time contributing member of the welding forums for Miller and Hobart.

    The oldest dinosaur machines out there typically have an open-circuit voltage of less than 70 V. Voltage during welding is typically in the 20s.

    I've put my work lead against more EMT that I can remember.

    Interesting tangent perhaps: It's not really a "ground lead" as it's part of the current path, and can be any polarity, depending on the process.

    EDIT: I now think you mean the exterior metal armor of a large MC cable was arcing against some EMT. Yes, this could be possible if that became the short circuit of the welding current flowing along the raceway. Sounds rare, but possible. Did it put a hole in the armor?
    Last edited by MAC702; 11-26-17 at 10:13 AM.

  3. #3
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    Quote Originally Posted by MAC702 View Post
    EDIT: I now think you mean the exterior metal armor of a large MC cable was arcing against some EMT. Yes, this could be possible if that became the short circuit of the welding current flowing along the raceway. Sounds rare, but possible. Did it put a hole in the armor?
    That's what was happening and it was determined that they had connected the lead directly to the metal armor of the MC cable. The armor had a burn spot but hadn't made a hole yet. The contact was intermittent and only occurred if someone pushed the MC cable against the EMT.
    Rob

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    All responses based on the 2014 NEC unless otherwise noted

  4. #4
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    IMHO it is an NEC violation to use either a wire or a raceway EGC as the current return path on either the primary or the secondary side of the welding transformer.
    It is 100% objectionable current in either case. I am sure that it is contrary to the use instructions of the welding equipment too.
    It does not make any difference that this is a temporary setup during construction.
    As a practical rather than code issue, using building steel for the entire return would be less hazardous than using an EGC as part of the path. Still illegal though.
    And, as previously mentioned, part of the encouragement for this violation is erroneously thinking of the welding lead as a "ground" rather than a grounded current carrying conductor.
    Sent from my XT1585 using Tapatalk

  5. #5
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    Quote Originally Posted by GoldDigger View Post
    ...using building steel for the entire return would be less hazardous than using an EGC as part of the path. Still illegal though...
    I think you just shut down the entire welding industry.

  6. #6
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    Quote Originally Posted by MAC702 View Post
    I think you just shut down the entire welding industry.
    Cool, I knew he was a smart feller, but that's impressive.
    "Electricity is really just organized lightning." George Carlin


    Derek

  7. #7
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    so the clamps in the pic are secondary clamps?? is it a TIG machine?
    if so they might likely be there in case the work piece primary clamp falls off during welding.

    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.

    Some welding machines use starting and stabilizing circuits that contain high-frequency voltage. This is common on gas tungsten arc welding (GTAW) machines. The high-frequency voltage may have frequency components that are in the megahertz range. In contrast, the welding voltage may be as low as 60 Hz.
    High-frequency signals tend to radiate away from the welding area. These signals may cause interference with nearby radio and television reception or other electrical equipment. One way to minimize high-frequency signal radiation is to ground the welding circuit. The welding machine instruction manual includes specific instructions on how to ground the welding circuit and components in the surrounding area to minimize the radiation effect.
    so when you clamp your workpiece you essentially have clamped to the egc. std practice, and i dont think this caused any issue for any wiring.

  8. #8
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    Quote Originally Posted by FionaZuppa View Post
    so the clamps in the pic are secondary clamps?? ...
    I had assumed multiple welding machines and multiple weldors.

  9. #9
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    I have only worked with smaller MIG and TIG welders in non-building-construction applications. But in those applications I regard it as extremely stupid to ground the work table and run the welder return lead to some remote grounded object. The return lead should be placed on the work, as close as practical to the welding location. Grounding the work or work table may also be a good idea, but not if it ends up being part of the return. Perhaps I'm missing something about other types of welding applications.

  10. #10
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    Quote Originally Posted by MAC702 View Post
    I had assumed multiple welding machines and multiple weldors.
    Yes, the three welding machines are just out of frame with about 10' leads connected to the EMT via those clamps in the photo.
    Rob

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    All responses based on the 2014 NEC unless otherwise noted

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