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  • Grounding question on multiple circuits/same conduit

    I have a question about the best/proper way to ground this installation. For a little bit of history I'm replacing the conduit in an apartment that was orginally all EMT with PVC. Over the years a lot of the EMT has rusted through thoroughly in many places completely loosing ground.

    The way the conduit run is laid out is two circuits start from the main panel through the same conduit. The first of the circuits feeds two receptacles at each of the first two junction boxes while the second circuit keeps running uninterupted through those two first JB's. At the second receptacle's JB the conduit then splits up two ways. The first circuit feeding those first two receptacles goes on to feed 5 more in that and a second room while the second circuit goes on to feed the first of 7 receptacles on a third room and family room.

    My question is: Should I run one ground wire from the panel and pigtail it off at the second JB to go with each of the circuits or should I run a second uninterrupted ground wire straigt through with the second circuit only for the receptacles fed by that circuit? This wasn't much of an issue before since the grounding was done through the EMT before but now I have that doubt. It doesn't sound like a good idea to have one ground wire grounding two circuits. Wiring is 12ga THHN on 20A breakers.

  • #2
    Re: Grounding question on multiple circuits/same conduit

    You only need one ground wire. It must be equal in size to your largest conductor. ie you could have a main conduit with ten circuits in it go to a junction box with a conduit for each of those circuits coming out of it. Assuming all are 20 amp circuits you would need to junction 10 #12 grounds to a single # 12 ground wire that goes back to the panel.

    EMT is no longer used as the sole ground in new installations you must run a ground wire within the conduit.

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    • #3
      Re: Grounding question on multiple circuits/same conduit

      The new ground must be spliced in every box along the way, to each metal box and to each other; 250.148.

      Don't forget that if any EMT is not connected to the ground wire, then it can become energized and not kick a breaker - be sure that the EMT is securely connected to the metal boxes, and to the ground wire, to bond it out.

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      • #4
        Re: Grounding question on multiple circuits/same conduit

        Ok excellent. Thanks for the responses! There is no longer any emt left so thats not a problem. All the electrical has been deteriorating since the late 1950's and I'm just taking it all out since its in very bad shape.

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        • #5
          Re: Grounding question on multiple circuits/same conduit

          Check your local electrical codes related to fires. Some areas still require all wire to be inside a metalic jacket or tube and all electrical boxes to be steel. In such cases you'll have to use EMT, IMT, BX or Greenfield as needed. As for grounding, each box and device needs good grounding. A single ground conductor with green insulation should work fine. If you need to splice it, be sure to make a good U and make good use of the grounding screws in the wiring boxes. If necessary you may want to have 2 grounding wires with one end connected to the grounding bar in your load center (breaker panel) and run them outward. Try to keep them as short and direct as you can. A good low resistance ground is a must for safety.

          I guess my thinking is to just think safety all the way and do the best you can with it. It's pretty hard to overkill grounding without going crazy.
          Last edited by Woussko; 07-29-2007, 09:56 PM.

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          • #6
            Re: Grounding question on multiple circuits/same conduit

            All construction here is concrete. The conduit goes encased in the concrete so its either EMT or PVC tubing. Conduit is the norm, there is no other choice. EMT fell out of favor many decades ago due to it being horribly prone to corrosion in the tropical enviroment(which is the problem I'm fixing). All the steel boxes are ground with green cable and grounding screw. I was just a little in doubt about that run that had two circuits starting through it. Wasn't sure if each circuit needed its own independent "home run" grounding wire or if it was ok to just split the same ground off for each circuit.

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