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grounds and ground faults on engine drives question

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  • grounds and ground faults on engine drives question

    Can someone tell me how a ground fault works on a engine drive that is not sitting on the ground or does not have a wire going to driven ground rod. My 12,000 watt home generator says it has to be placed on the ground when running to avoid getting shocked or possibly killed. Also could a ground wire coming off a engine drive's ground welding terminal to a driven rod help welding characteristics and safety. I know Miller has the specialists to keep things safe but I would like to know if it's safe to run a welding generator on a trailer that doesn't have a metal wheel or pad on it's tongue's jack stand to make a ground or a wire going from a trucks' bed to a driven ground rod.
    Last edited by tackit; 03-25-2013, 10:37 AM.

  • #2
    I have some welding to do this spring on my gates. I'm planning to use this cart I built to hold my 12,000 watt generator and my MM180.... as you can see the trailer tongue's jack I made from a grocery cart wheel whose tire is made of rubber, there is no ground for the generator as the trailer sits. I think it's a legitimate safety question for anyone with a similar set up.


    • #3
      The word Ground is the problem.

      A rod driven in to the ground does not offer protection per se for Ground faults it is there for High Voltage strikes like lightening or if a downed power line came in contact with the machine.

      Using an engine drive as a welder/generator or a stand alone generator on a jobsite you DO NOT need to drive a ground rod.

      Using it as back up power for a building then a ground rod or connection to a building ground is required. But again this does not provide the Protection that the Ground wire in the electrical system provides.

      This is more of a BONDING issue. You want all metallic parts in the system Bonded to the ground wire because the Ground wire is bonded to the Neutral at the main panel.

      The fault will travel down the Ground wire meet up with the Neutral wire at the main panel, travel up the neutral wire to the Transformer and overload the circuit-tripping the Circuit breaker.

      This is why in the manual for the Engine drives they indicate using a metallic strap from the Engine drive to the Trailer to Truck bed

      It does not travel in to Mother Earth and magically stop.

      Tongue Jacks: You actually want to isolate the Engine drive or generator from the earth. (it is code here). The earth may provide an alternate path for the ground fault. Example is- the tool you are using faults, goes through YOU, down to earth and back to the power source instead of going through the Ground wire.
      Remember that it is a CIRCUIT and the electricity is always looking for a return path to the source. Normal conditions it takes either the Neutral (120v) or a hot leg (240v etc). Fault= whatever is the easiest path.


      • #4
        Ground faults (GFI) works the same way as one in your bathroom,, no ground rods involved, the unit just looks for a quick way for the 120vac to touch the circuit common( welder frame) then it shuts the power off.

        I, like many, find this to be a stupid and troublesome thing on a welder. especially in snow, rain, or humity, thus they are disconnected or made to look functioning but in reality don't do squat. Who wants to repeatily run back 100+ ft every time the stupid thing trips.


        • #5
          Thanks cruiser, I appreciate you sharing your electrical knowledge with us. I'm going to read your comment a few times and save it for future reference. Thanks again, you're a great asset to the board, tack


          • #6
            Thanks brocc, I appreciate your input too.


            • #7
              How does a GFI work

              It turns out that a GFI does not need a ground connection to work. It measures the current in the hot lead, and compares it to the current in the neutral. If the difference between the two currents is more than 6ma (0.006 amps), then it cuts off the power until the GFI is manually reset.


              I am not sure that a GFI makes a lot of sense for a portable generator which is not grounded. I guess if you have a wet power tool and touch the generator it might protect you.

              One of the reasons that welding is relatively safe is because the secondary coil of the transformer is isolated from ground. Note that the welding cables are labeled "work", not "ground", although I sometimes get sloppy and say ground. The comment about isolating the generator from ground makes sense to me, although I don't know what the code says.

              I have noticed that the GFI in my shop often trips when I am welding.

              The concept of "ground" is much more complex than most people understand. Ground is not necessarily ground.



              • #8
                It is a City of Los Angeles code



                • #9
                  Thanks Richard, it's interesting even though it's confusing to me. Where does the ground pin on a 120 v plug go to? The neutral in the panel box and then back up the pole to the transformer? Please don't say back to ground.....:-)


                  • #10
                    Good info Brocc. thanks This from your source, down at the bottom it explains grounds in understandable language.



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