Announcement

Collapse
No announcement yet.

installation and max length of GEC to UG metal water pipe

Collapse
X
 
  • Filter
  • Time
  • Show
Clear All
new posts

    installation and max length of GEC to UG metal water pipe

    I have a dry type transformer about 100 feet away from the building it is serving (pump house). We have a panel inside the building. A metal water pipe enters the building from underground up through the slab about 30 feet from the panel, roughly in the middle of the building. How would you route the grounding electrode conductor to the waterpipe: exposed, rmc, pvc etc? The grounding electrode conductor to the water pipe may be 60 feet long, is there a limit to how long the GEC could be?

    #2
    Originally posted by xguard View Post
    I have a dry type transformer about 100 feet away from the building it is serving (pump house). We have a panel inside the building. A metal water pipe enters the building from underground up through the slab about 30 feet from the panel, roughly in the middle of the building. How would you route the grounding electrode conductor to the waterpipe: exposed, rmc, pvc etc? The grounding electrode conductor to the water pipe may be 60 feet long, is there a limit to how long the GEC could be?
    The GEC needs to go to the grounding electrode in the building the transformer is located in not the building it is supplying.

    At the building it is supplying you need another grounding electrode system that you will connect to the EGC of the transformer secondary.

    And no there is no length limit for a GEC.

    Comment


      #3
      Thanks! The transformer is located outside, and has it's own grounding electrodes. At the building as you said, I was going to connect all electrodes present to the EGC of the panel (neutral and ground not bonded, only bonded in the transformer). Is this what you are describing?



      Originally posted by iwire View Post
      The GEC needs to go to the grounding electrode in the building the transformer is located in not the building it is supplying.

      At the building it is supplying you need another grounding electrode system that you will connect to the EGC of the transformer secondary.

      And no there is no length limit for a GEC.

      Comment


        #4
        Yes, you only bond neutral to ground at the transformer or the first over current device on the secondary side.

        Comment


          #5
          Originally posted by xguard View Post
          How would you route the grounding electrode conductor to the waterpipe: exposed, rmc, pvc etc? ...
          I would comply with 250.64. Specifically, it can be exposed if 250.64(B) does not apply, but that's rarely the case for the entire length. RMC is allowed but so is EMT which is a lot cheaper and easier. PVC is allowed. Or depending on the required size you could probably buy single conductor armored cable which is made for this purpose. Be sure to get appropriate fittings for bonding both ends if using ferrous metal.

          Comment


            #6
            It’s interesting that 250.64. never mentions about any restrictions in routing the GEC. People had learned not to get near a tall tree during lightning storm due to the lightning current going down the green tree could arc to the human body in searching for a less impedance path. In this example of routing 30 feet GEC from the indoor panel to the water pipe, is it safe for the GEC to running along a wall near a worker desk? I wouldn’t want to be 3 ft within that GEC when lightning. Since the main reason for installing ground electrode and GEC is for lightning protection, then why in this case not to connect GEC to the grounded conductor (neutral) at the service entrance outside the building instead of the indoor panel?

            Comment


              #7
              Yes this is somewhat of a shortcoming of the NEC.(and don't get me started on 690.47(D), you can google that with Mike Holt to see what I mean). And I believe part of the reason is that lightning isn't the primary reason for the GEC nor for all the various extra bonding requirements. The NEC is mostly concerned with electric shock hazards to personnel and keeping stray power voltages off of exposed parts and stuff. There's another code for lightning protection and you should not rely on the NEC if you want to keep yourself safe from lightning hazards. I'm thankful I don't live in a high lightning area where I'd feel bound to argue NEC vs. lightning saftey all the time.

              Comment


                #8
                Many believe ground electrode and GEC are for protecting from electrical shock hazard by stray power voltage on exposed metal structure, including professionals who install street signal light poles. Sadly some of them only have the metal pole body connect to a ground rod. A 120v shorted to the pole will create gradient voltage on the soil, with voltage increases from the pole towards distance from it. E.g. stand 3 feet away will get a 50v shock when touch the pole. To solve the problem, the pole should be connected to grounded neutral conductor for a low resistance return path to open the over current protection device.

                Comment


                  #9
                  Originally posted by Brian Dang View Post
                  Many believe ground electrode and GEC are for protecting from electrical shock hazard by stray power voltage on exposed metal structure, including professionals who install street signal light poles. Sadly some of them only have the metal pole body connect to a ground rod. A 120v shorted to the pole will create gradient voltage on the soil, with voltage increases from the pole towards distance from it. E.g. stand 3 feet away will get a 50v shock when touch the pole. To solve the problem, the pole should be connected to grounded neutral conductor for a low resistance return path to open the over current protection device.
                  The pole should have an EGC ran to it. The grounded conductor is not allowed to be used as an EGC under the NEC.
                  If Billy Idol is on your playlist go reevaluate your life.

                  Comment


                    #10
                    This should further my point on installation of GEC at the outside service entrance:

                    “Having established that the general purpose of the grounding electrode system is to provide a path to ground for high-voltage surge currents and lightning strikes, keeping the grounding electrode conductor outside the building would be common sense. However, the NEC does not require this conductor to be routed outside of the building.
                    For example, if a concrete-encased electrode has been installed on one side of a building and the service on the other side, an electrician could install the bare grounding electrode conductor up the side of the building, through the attic, and down to the service equipment on the other side. In this case, any current from surges, lightning and unintentional high voltage would then be routed along the grounding electrode conductor connected at the electrical service, through the attic, and down to ground on the far side of the building. This could create a very dangerous situation with the possibility of fire and destructive voltages in the building.
                    Understanding the basics for grounding electrode systems should prompt the installation of grounding electrode conductors on the outside of the building or in the ground surrounding the building rather than inside, whenever possible. EC”

                    From link: http://www.ecmag.com/section/codes-s...ctors-building

                    The AHJ should fail this installation example. It might not obvious violate the code but the long GEC looses its usefulness and even posing fire hazard. To be able to respond fast to high frequency current of lightning strike or voltage surge, GEC should have very small impedance, which requires short length and larger gauge wire, and install in a straight line as possible. High frequency current doesn't like bent wire just like race cars on race track.
                    Last edited by Brian Dang; 04-26-16, 07:55 PM.

                    Comment


                      #11
                      All that just bolsters my point that the people who make the NEC are not viewing the GEC as having the purpose of protecting things from lightning. If they did the requirements would be a lot different and there would be exceptions to certain requirements for certain circumstances. Thankfully not all of us live in places where we have to worry about lightning that much. For the rest of you, there's NFPA 780, etc.

                      Comment


                        #12
                        For the OP, are the conductors under ground or overhead, from the transformer to the pump house? If they are not subjected to lightning then the GEC is only for earth voltage reference to prevent shock hazard -- low frequency current -- then it's length is less critical

                        Comment

                        Working...
                        X