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Thread: Welder Ground Lead

  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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  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.

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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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  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

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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.

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    Quote Originally Posted by GoldDigger View Post
    ...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...
    To clarify, it is also not a grounded conductor. It can be any polarity.

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    One would think that with this setup, using the building electrical system as part of the welder circuit would yield lousy results.
    Rob

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    Quote Originally Posted by infinity View Post
    One would think that with this setup, using the building electrical system as part of the welder circuit would yield lousy results.
    Using metallic conduit near the welding machine is often the most (and sometimes the only) convenient way to clamp onto the building's common bonded steel structure, needing only the electrode lead (stinger or wirefeeder) to be strung to the other part of the structure that you are welding something to.

    I've never seen the work lead clamped onto MC though, and would not think it appropriate, but EMT wouldn't give me a second thought, right or wrong.

  9. #9
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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

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    Quote Originally Posted by MAC702 View Post
    Using metallic conduit near the welding machine is often the most (and sometimes the only) convenient way to clamp onto the building's common bonded steel structure, needing only the electrode lead (stinger or wirefeeder) to be strung to the other part of the structure that you are welding something to.

    I've never seen the work lead clamped onto MC though, and would not think it appropriate, but EMT wouldn't give me a second thought, right or wrong.
    This is in an all concrete high rise building with no structural steel. The welding is for gas piping, supply and return chilled water, etc.
    Rob

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