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Attempting to fix subpanel

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  • Attempting to fix subpanel


    Sorry if this topic has been covered before, I am new to the forum. I just bought a home that has some questionable wiring, and I am working hard to correct everything. The main 200amp service to the home is fine, but there's a subpanel in a detached shop and separate detached garage that concern me.

    They ran 2 conductors and 1 neutral to the shop, but no ground. At the subpanel the neutral and ground are bonded together. From everything I've read, you do not bond them at a subpanel. To correct this, I separated all the neutrals from the grounds on separate bus bars. I then drove 2 ground rods, about 10 ft apart and connected the ground bar to them with 6 gauge wire. Was this the correct thing to do?

    Same basic problem in the detached garage. It is fed from the shop subpanel and has the same issue, only ran conductors and neutral, but no ground. I repaired the garage subpanel the same way.

    All outlets show correctly with a tester, but I know that doesn't prove anything.

    Thanks in advance,
    Tim

  • #2
    First of all I am not a electrician,

    But without running a ground wire, from the main panel to each subpanel, I am reasonable sure your not up to current code,

    the problem with the system you have is there can still be voltage a difference between the the ground and the neutral,

    the ground plain potential is not necessarily, the same in the design you have, (yet the basic set up was done for years pre 70's),
    on my farm some of it buildings were set up very similar, (pre ground wire days), (the difference was I have a distribution pole, where the power is separated, and not a power panel), (as setup similar as in a city where a couple of houses are ran from one transformer on a pole, and each house is its own service),

    If you were from a distribution point the extra ground may or may not be needed, (I know now they are wanting the ground wire now ran from a distribution point as well in many if not all instances), and also when it was installed, and what code cycle it was done under,

    IMO the setup is not dangerous, but may not be as "safe" as modernly posible,

    ~~~~~~~~~~~~~~~~~~~~~~~~

    for years the understanding of stray voltages, was not really understood, and by connecting all the grounds on a location to one point, creates a ground plane that is the same in all locations,

    the nuterals of the power company are connected at each and every pole, and transformer, and electricity flow (the old saying was the path of least resistance), well now it is said it takes all paths back to source, thus depending on where one is located and what is around one, there can be stra voltages passing through the ground at varying voltages,

    this is why sometimes swimming pools can give a person a tingle when entering the water,
    the same problems can create problems on farms as many animals are very sensitive to voltage diffrentals,
    Push sticks/blocks Save Fingers
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    PUBLIC NOTICE: Due to recent budget cuts, the rising cost of electricity, gas, and oil...plus the current state of the economy............the light at the end of the tunnel, has been turned off.

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    • #3
      You have created a dangerous condition. Without a neutral to ground bond, the resistance to the ground conductor is too high to to trip a breaker if a ground fault occurs. The best plan would be to run a ground wire back to the main panel where you have a neutral to gound bond. If that is not practical, reestablish the neutral to ground bond at the sub panels.

      The wiring method you found existing (2 hots and a neutral bonded to the ground) was permissible (with certain conditions) under old code cycles and still is grandfathered.

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      • #4
        Seems to me that you now have three grounds which could each have a different potential to ground, not good as has already been stated above.

        I take it the outbuildings are some distance from the main panel. How is power distributed to these other buildings, is it overhead or underground in conduit?
        "It's a table saw, do you know where your fingers are?" Bob D. 2006

        https://www.youtube.com/user/PowerToolInstitute

        ----

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        • #5
          Originally posted by Bob D. View Post
          Seems to me that you now have three grounds which could each have a different potential to ground, not good as has already been stated above.

          I take it the outbuildings are some distance from the main panel. How is power distributed to these other buildings, is it overhead or underground in conduit?
          While your statement is true it is not the real problem. If he has a ground fault in one of the out buildings all of the metal parts connected to that ground will be at 120 volts. Not enough current will flow to trip a 15 or 20 amp breaker due to the impedance (resistance) of the ground rods being too high. He needs to establish a neutral to ground bond back to the main panel. Or alternately establish the bond in the sub panels that he removed mistakenly thinking he was correcting the issue.

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          • #6
            Thanks all. I'm going to go ahead and re-bond the neutral and ground bars to resolve the issue. Just tell me I added "some" value to the system by adding those ground rods, so all my labor and expense wasn't for nothing?

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            • #7
              You should make this up to the current standard making sure what if any additional requirements your municipality might have. Grandfathered or not your not getting the maximum protection that you easily could have.

              It shouldn't be to hard to add a ground wire and run it underground from each sub panel back to the main panel, then your in compliance.

              Your obviously trying to do the right thing, don't stop now.

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              • #8
                Yep, I will take the time to run a ground from the main panel as soon as possible, I want this done correctly. It may not be simple though, it's 1.5" conduit running underground (and under shop slab) for about 75 feet, with at least three 90 degree turns in it. Once I have the ground wire run, I should then attach to grounding bar in subpanel correct? And then remove the bond between neutral and ground at the sub, or does it still stay?

                Thanks for all the advice!

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                • #9
                  Do you plan to pull the ground wire through the existing 1-1/2 conduit with the hot and neutral still installed?

                  Any idea how old the existing conductors are. Pulling a new ground wire through with existing wires in the conduit you need to be careful not to damage existing conductors. It might pay to megger existing conductors before your pull and again afterward to ensure no damage done.

                  You could also pull the old stuff out; swab/clean out the conduit if inspection of the old cable revealed lots of debris, dirt, or water in the conduit; then pull all new stuff in. That would be expensive, but then so would damage to an existing conductor which would put you into pulling new wire anyway.

                  "It's a table saw, do you know where your fingers are?" Bob D. 2006

                  https://www.youtube.com/user/PowerToolInstitute

                  ----

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                  • #10
                    Originally posted by timmed View Post
                    Yep, I will take the time to run a ground from the main panel as soon as possible, I want this done correctly. It may not be simple though, it's 1.5" conduit running underground (and under shop slab) for about 75 feet, with at least three 90 degree turns in it. Once I have the ground wire run, I should then attach to grounding bar in subpanel correct? And then remove the bond between neutral and ground at the sub, or does it still stay?

                    Thanks for all the advice!
                    I would not try to add the ground wire with the existing conductors in place. Pull everything out, add the ground wire (1 size smaller than the hots) to the bundle and re-pull. Use plenty of wire lube and a helper.
                    Once you have added the ground wire to make your feeder 4 wire compliant, remove the bond in the sub panels.

                    If it were my installation, I would leave it as 3 wire with the neutral to ground bond in the sub panels. It was compliant when installed and there is no real reason the change. Is it unsafe? Only in the very unlikely event if the neutral back to the panel were to go open.
                    Last edited by rjniles; 03-26-2018, 07:33 AM.

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                    • #11
                      It was code compliant to run a 3-wire feeder to a outbuilding as long as there were no parallel metallic paths to the building, so for example if there was a metallic water line between them it was not OK, but if none then it was allowed, it was removed as being allowed method several NEC editions ago, as long as it's existing it can remain, but does require a grounding electrode.

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