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  • Sub Panel

    I'm looking to replace my old mig Hobart I've had for the last 7 years with a nice TIG machine

    I have an old house with a 100 amp load center, and I just ran a 60 amp sub in the garage. I had a question about grounding. Does it make a difference if a TIG machine is on an isolated ground or not? The load center is original and back from the mid-60s, a 100 amp GE with the ground tied directly on the neutral bar.

    I just added a square D 60 amp sub, with no separate ground (runs directly back to the main)

    Would it make a difference if I pounded a ground rod in and isolated the sub panel?

    Thanks

  • #2
    In my area that would be out of code.

    You have the right idea just the wrong location. Get a grounding rod and drive it in near the load center and ground the load center to it along with a water pipe. Use 6 AWG THWN II wire (Green). Then you would run a ground from your sub back to the load center. This is called floating the panel. This prevents Ground loops or an alternate path to ground and also prevent the ground at the panel from potentially having current across it.

    And anything installed after the fact would have to have it's ground run back to the load center. i.e. no disconnected grounds anywhere along the line.

    Home depot and Lowes have a handy little book called "Code Check" they have them for all type of construction. Get the electrical version about $16.00 it will explain sub panel grounding.
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    • #3
      I wouldnt do anything unless I had a problem, use it first.

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      • #4
        kcstott is correct.

        Per the NEC (National Electric Code) all subpanels must have a separate common and ground running back to the main panel, so all grounds terminate at one point, the main panel. The subpanel needs to have 2 busses installed, one for common and one for ground, and all branch circuits connected to the subpanel wired separately to the two buses.

        In other words, your subpanel must have 4 wires running back to the main panel, 2 hots, 1 common and 1 ground.
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        • #5
          Grounding

          A ground line is not only inexpensive but a good idea.

          The smart way is to get a ground rod from your electric supplier. They are copper plated steel these days.
          The old way is to run a ground wire to an outdoor fausit - only if it is galv pipe. both are better than nothing.
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          • #6
            Talk to your electrical inspector before you do anything. There's specific guidelines as to how to install a ground rod and what size wire needs to attach to it. They'll set you straight, and they'll be inspecting it - so find out what they want before you do anything.
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            • #7
              We assume this is an attached garage? If so it doesn't need any ground rods or connections to water pipes. If its a separate building it needs a rod and minimum of number 8 connecting it for 100A service.

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              • #8
                This went very off topic. I work in a substation maintaining high voltage equipment; I'm very familiar with what is required as far as proper grounding. The sub panel is already properly grounded.

                I was asking if the welding machine would require an isolated ground, or if it would make a difference if it had one. Any help?

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                • #9
                  As long as your cord, plug, receptacle, & sub panel are properly bonded and grounded. There would be no real advantage to a separate grounding rod.

                  Typically we see this set up on machine tools with Microprocessor control i.e. NC/CNC this is used to eliminate electrical noise that may play with encoder signals. Never seen a welder hooked to one. I couldn't hurt though.

                  I was under the impression you want to drive in a grounding rod for the sub panel.
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                  • #10
                    I remember reading somewhere that most Tig machines reccommend it. We got a Synchrowave where I used to work, and when we first tried it out we had problems with it when plugging into certain outlets it would screw with the computers in the office. Plus, one time I had a bad gnd welding aluminum, and smoke started rolling out of the bench grinder next to me...It's an older building, so it may have just been the wiring wasn't up to par. But I personally would say a dedicated ground would be good insurance on the rest of your electrical stuff.

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                    • #11
                      Unless I had interference I wouldn't do anything, they do call for some shielded wiring within certain distance from unit in some installations but sheet, no one does it.

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                      • #12
                        Originally posted by dsmpower View Post
                        This went very off topic. I work in a substation maintaining high voltage equipment; I'm very familiar with what is required as far as proper grounding. The sub panel is already properly grounded.

                        I was asking if the welding machine would require an isolated ground, or if it would make a difference if it had one. Any help?
                        No one here knowed where ya work- weez just tryin' to help

                        http://www.millerwelds.com/om/o353u_mil.pdf

                        Look at section 6-3

                        Should answer your questions.

                        and as Sberry said.. Plug in the machine and weld- interference? then ground as per the instructions in the manual.

                        I don't on mine- 100amp Main Panel, detached geerage Sub panel
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                        • #13
                          wire sub panel to code and get it inspected. Keep your insurance valid.
                          try using the weld and see if it causes any problems. If it does you can then drive a ground rod next to the welder and connect a cable from it to your weld case and you welding table. DO NOT REMOVE THE GROUND FROM YOUR ELECTRICAL PANEL. It is needed to make sure your breakers trip in the event of a short. I have seen one shop that had a lot of PLC controls in the next room and the HF from the tig messed them up big time. They put in the ground rod for the machine case and table, then sent a bare copper wire up the wall across the ceiling over the table and across the room. Touching every conduit they could along the way, the wire acted like an antenna and gave the HF a path to ground. There are many ways to control HF, Just have to try some of the low cost ideas first. Good luck.
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