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  • Electrical Grounding Question - Detatched Garage

    A friend of mine is having a problem where his electrician and the inspector can't agree which way is correct. What is your take on this?

    On his property he has a garage that is about 100 feet from his house. There is no plumbing and there will be no telephone, data or cable TV connections. The garage is fed from the main load center (breaker box) in the house and 6-3 with ground direct burial cable was used. In the garage is a small load center (breaker panel). The issue is does he need to drive a ground rod just outside of the garage and connect it to the ground bar in the garage load center? The inspector says yes and the electrician says no. I'm thinking there can be a problem as the actual potential between two different grounds comes to mind. This would mean there will be a constant small current flowing in the ground wire which connects the main load center to the one in the garage. I also can see from a safety point what the inspector has in mind. A third option might be to only use the connection to the ground rod near the garage and not connect either end of the grounding conductor of the feed cable.

    What would you do? This is out in the country and once it passes inspection things could be changed based on what really is the correct way.

    A second electrician from the same area said he has done it both with a ground rod for a garage and also without. Both ways passed inspection and he sees advantages and disadvantages. I personally am on the fence and take a neutral side.

  • #2
    Re: Electrical Grounding Question - Detatched Garage

    If I'm reading section 250.32 (A) correctly, and please correct me if I'm not, the inspector is right. The electrician may be thinking of the exception for that section but that's only for single branch circuits and not for feeders to panels.

    I would drive the ground. Why?
    1) It's cheap and easy.
    2) Nobody ever complained of too many grounds.

    If it were my job I would just do it. It would be in the bid.

    Comment


    • #3
      Re: Electrical Grounding Question - Detatched Garage

      I would say no. Afterall all grounding is done at the main disconnect, since it is at a subpanel, and fed with a 6-3 cable rated for direct burial, that cable assembly already carries a separate neutral conductor AND a grounding conductor all the way back to the main disconnect. Now of course in the subpanel the grounding and neutral bars need to be kept separate, so make sure whatever bonding jumper between the two is removed. As for the grounding means itself, well, if there isn't a gounding means in at the main disconnect, such as ground rods and/or waterpipe bond, definately put them in, but only for the main disconnect.

      The only time, if I am reading the code right, a separate ground is needed for a separate structure only when it has it's own service. I know there are inspectors out there that get a bit overzealous when it comes to grounding.

      Oh and driving a ground rod down is never easy, or cheap, especially up in the hilly terrian.

      Comment


      • #4
        Re: Electrical Grounding Question - Detatched Garage

        Cite the code section please. Like I said, the exception to 250.32 is for branch circuits. This, because it has a panel, is a feeder. Therefore a separate ground is specified. Once again: if I'm wrong then cite the code. I'm using 2005 NEC and have copies at both desk and in all the trucks as well as Ugly's. I'm open to learning and finding out new stuff but you have to prove it.

        As far as ground rods go: if you have trouble driving them find another profession. I work exclusively in the Santa Cruz Mountains and must have driven over 50 rods last year. There's lots of shale and rock here. I use a $500 rotohammer for the job, strap a tie down to it, and stand on it. Even then sometimes I have to cut them and drive another. It's part of the job. If you find it difficult then move over and give me the job.

        Comment


        • #5
          Re: Electrical Grounding Question - Detatched Garage

          I would vote for the ground rod,
          Push sticks/blocks Save Fingers
          ~~~~~~~~~~~~~~~~~~~
          "The true measure of a man is how he treats someone who can do him absolutely no good."
          attributed to Samuel Johnson
          ~~~~~~~~~~~~~~~~~~~
          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.

          Comment


          • #6
            Re: Electrical Grounding Question - Detatched Garage

            For what this is worth, the ground rod is already in the ground. That was the easy part in this case. Yes it took a bit of good old grunt and groan with a sledge hammer but that can be fun work. I'm in favor of it, but please try my little test sometime and observe what happens.

            A) Drive a ground rod into the ground and then another one 100-200 feet in a straight line from the first one.
            B) Connect a wire to ground rod #1 but not to ground rod #2.
            C) Get your trusty VOM such as a Simpson 260 or Triplett 630 out and connect the common lead to the ground rod with the wire attached.
            D) Set it to the 1000 Volts DC scale and touch the red test lead to the ground rod without the wire connected.
            E) Depending on what you read, disconnect the red test lead and set to a lower DC Volts range.
            F) Repeat steps D & E but this time set it for AC Volts.
            G) Please report your measurements.

            This would be the only good reason I can think of for NOT connecting a ground rod to the load center ground bar in the garage.
            I still think for safety that I'm in favor of the ground rod and connecting it.
            Last edited by Woussko; 06-21-2009, 04:57 PM.

            Comment


            • #7
              Re: Electrical Grounding Question - Detatched Garage

              ever power pole is grounded (in our area) and attached to the Neutral on the high voltage,
              right or wrong, every building is grounded and that is on a 3 wire system so the neutral is grounded/earthed at ever building as it is considered it own service from a distribution point,

              the stray voltage is more than likely induced voltage from the power lines or other, you reading that is traveling thought the ground, and it taking a short cut through the electrical system, this is where swimming pools, dairies and other animal confinement have such problems and that is why the equipotential and massive bonding requirements are such as they are is to bring ever thing metal up to the same electrical potential, like a bird setting on a wire, it may be a 1000's volts of power in that wire but the bird is one with it so it is not bothering it,
              you look at bonding requirements on things to day when it is done being bonded, (it is grounded in many many locations) as the bonding is hooked to the ground/earth.

              In my area I an not sure I would be bothered much by stray voltage, as there is very little other on the back side of me, away from the sub station,
              but in theory if there was power lines on the back side of me and zigged zag ed behind me, and other power using items, some of the flow of power would be through the ground, heading straight back to the sub station, and I can see how it would be possible to pick that up and in homes the neutral coming in from the transformers is bonded and grounded on the same wire of the pole as the high voltage is, so IN a sense your tied into the potentials of leakage of the power providers equipment as well, but since normally your on the same potential, (walking on the ground), you will never see that it is energized unless one does just what you described above,

              I suppose if you wanted to reduce any or nearly all the stray voltage from ones location one would need to run a grid of wire under the property to gather and consolidate all that stray voltage and make a huge plane of equal voltage under the property, similar to what is required in dairy barns and swimming pools,

              and if your having stray voltages your and it is not do to the power company's power distribution then your have a ground neutral connection some where, (which is common in older wiring such as the dryer, welder, range, and other 240 volt loads who use a ground neutral combination,) which has been changed in the code in recent years thus the 4 wire set up now, so one does not tie the neutral and the ground together.

              some info on stray voltages,

              http://www.bassengineering.com/SV_Cause.htm

              http://www.emfrelief.com/stray.htm
              Push sticks/blocks Save Fingers
              ~~~~~~~~~~~~~~~~~~~
              "The true measure of a man is how he treats someone who can do him absolutely no good."
              attributed to Samuel Johnson
              ~~~~~~~~~~~~~~~~~~~
              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.

              Comment


              • #8
                Re: Electrical Grounding Question - Detatched Garage

                First and foremost, I'm NOT an Electrician. I am somewhat familiar with the code from having done some of my own electrical work, including putting in my own service a decade or so ago. (Yes, it passed inspection!)

                I'd go for the ground rod at the garage. Personal opinion is that the length of the run is just too long to be absolutely dependable, by itself. Any future flaw that may add to the resistance or integrity of that long ground wire would immediately jeopardize the safety of the electrical system in the garage.

                The addition of proper, to code (in my area, that means a couple of ground rods, spaced and electrically bonded together) grounding rods would be cheap, pre-emptive ensurance of a safe system.

                My opinion anyway,

                CWS

                Comment


                • #9
                  Re: Electrical Grounding Question - Detatched Garage

                  Unless he's telling you to do something unsafe its generally best to just do what the inspector wants it saves everyone time(thus money).

                  If I was given option of driving a ground rod vs running a 100 feet of grounding conductor I'd opt for the rod.

                  Comment


                  • #10
                    Re: Electrical Grounding Question - Detatched Garage

                    Since the garage is a separate building and not attached to the main house where thr power is coming from, it is treated as a separate building. Therefore, when feeding a panel in the garage the line from the main house to the garage is a feeder NOT a branch circuit. So, you would send over 2 hots and a nuetral with no ground. At the panel in the garage you would establish a ground with a ground rod just like the power company only sends 2 hots and a nuetral to your house with no ground. You establish a ground at the building with the ground rod there. If you sent over one circuit as a branch circuit with no load center, then you would only need a ground from the main building with no rod. But in this case there is a load center so you send 3 wires only and make the ground at the garage with the ground rod there.

                    Comment


                    • #11
                      Re: Electrical Grounding Question - Detatched Garage

                      You could run a ground too. Nothing wrong with that and it might take care of some of the potential difference between local ground rods. Not required but not really a bad idea. Again: nobody ever complained about too many grounds.

                      I was third in sales in CA last year for Guardian Generators by Generac and installed every one I sold. While every system got it's local ground as required, they also got a ground pulled with the power pull and bonded to the switch and main. I explained this to every customer and how the cost was minor considering the job and got approval for every one. All the inspectors also liked it. I drove a lot of ground rods between the gensets, the panels and the new services....

                      Comment


                      • #12
                        Re: Electrical Grounding Question - Detatched Garage

                        If the area is under the 08 code, then 4 wires are required as a feeder to the garage, and a ground rod must be driven.
                        The ground rod is not for grounding the garage, as this is done with the ground wire from the main panel, but for a place for the lighting current to flow, and not run back to the main panel.

                        Comment


                        • #13
                          Re: Electrical Grounding Question - Detatched Garage

                          As of today it's in and passed inspection.
                          I'm thinking it would be good for everyone to keep expressing themselves and how they think this should be done.
                          Last edited by Woussko; 06-22-2009, 02:15 PM.

                          Comment


                          • #14
                            Re: Electrical Grounding Question - Detatched Garage

                            Originally posted by jbfan View Post
                            If the area is under the 08 code, then 4 wires are required as a feeder to the garage, and a ground rod must be driven.
                            The ground rod is not for grounding the garage, as this is done with the ground wire from the main panel, but for a place for the lighting current to flow, and not run back to the main panel.
                            It was that last sentence that tripped me, I was thinking along the lines as the main grounding means. I knew that as a subpanel, the neutral and grounding conductor had to be carried separately back to the main, though the grounding conductor inside the cable assembly would put both grounding means at the main and the ground for the garage at the same potential.

                            Comment


                            • #15
                              Re: Electrical Grounding Question - Detatched Garage

                              Originally posted by jbfan View Post
                              If the area is under the 08 code, then 4 wires are required as a feeder to the garage, and a ground rod must be driven.
                              The ground rod is not for grounding the garage, as this is done with the ground wire from the main panel, but for a place for the lighting current to flow, and not run back to the main panel.
                              The ground rod must be driven at the sub under '05 code and '08 will require the addition of a ground pulled from the main. The ground rod is in fact for grounding the sub at the garage. The addition of the ground wire required for '08 compliance will ensure that all grounds of the system are at the same potential. There is no current flow through any ground anywhere at any time. It's a safety ground we require in this country. Many other countries do not require this. Current flows from leg to leg or from leg to nuetral (or vise versa depending upon electron flow or hole flow theory). Not through the ground.

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