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Thread: Water Pipe Bonding

  1. #1
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    Water Pipe Bonding

    What is the purpose of water pipe bonding?

    If it is to meet the requirements of either 250.4(A)(3) or (4), then why must the bonding jumper be sized per 250.66 and run to the service equipment and/or grounding electrode system.

    Other piping systems do not have this stringent of a requirement. Based on the wording, a 200A home could have only 2 ground rods connected by #6 as the grounding electrode system and then have a #4 water bond? Doesn't make much sense to me.
    Bryan P. Holland, MCP

  2. #2
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    Re: Water Pipe Bonding

    I first thought this was an easy question. The water pipe is a grounding electrode, and the GEC is to be sized per 250.66. Case closed. I would not question having a GEC to a water pipe being larger than a GEC to a ground rod. I would have asked the question from the other direction. My question would have been more along the lines of "why is it OK to have a smaller GEC, when you are connecting to a ground rod?"

    Then I took a closer look at 250 (a dangerous task, as we all know). I am now confused by something entirely different. 250.104(A)(1) says, in part, "The metal water piping system shall be bonded to (some things) OR to . . . grounding electrodes." Wait a minute. I though the water pipes were a grounding electrode. :confused:

    So we must be talking about water systems that do not connect directly to the incoming water supply. Drain lines and "grey water" lines, perhaps? So I have to ask, not having done this type of thing before: Do you bond all water lines? In every room? On every floor? If you see a pipe, should you see a wire also? Or if you bond once, on the first floor, do you not have to bond anywhere else? What is the actual practice? :confused: :confused:
    Charles E. Beck, P.E., Seattle
    Comments based on 2014 NEC unless otherwise noted.

  3. #3
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    Re: Water Pipe Bonding

    What I have are two houses that have internal water lines of copper that connects to a PVC pipe from the utility. Some of the water pipe is underground, some is through the attic space. All of the pipe is interconnected back to the house supply.

    So we are not talking about water pipe that can be accepted as a grounding electrode, but still, the bonding of this pipe is treated as such.
    Bryan P. Holland, MCP

  4. #4
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    Re: Water Pipe Bonding

    If you look at the commentary the 2005 NEC Handbook the requirement of 250.104 can be better understood. The commentary is as follows:
    Bonding the metal water piping system of a building or structure is not the same as using the metal water piping system as a grounding electrode. Bonding to the grounding electrode system places the bonded components at the same voltage level. For example, a current of 2000 amperes across 25 ft of 6 AWG copper conductor produces a voltage differential of approximately 26 volts. Sections 250.104(A)(1) and 250.104(A)(3) require the metal water piping system of a building or structure to be bonded to the service equipment or grounding electrode conductor or, where supplied by a feeder or branch circuit, to the building or structure disconnecting means or grounding electrode conductor. Information concerning bonding provisions for buildings with multiple occupancies and isolated metal water piping systems is contained in the commentary for 250.104(A)(2).
    In those cases where it cannot be reasonably concluded that the hot and cold water pipes are reliably bonded through mechanical connections, an electrical bonding jumper is required to ensure that this connection is made. Some judgment must be exercised for each installation. The special installation requirements provided in 250.64(A), 250.64(B), and 250.64(E) also apply to the water piping bonding jumper.
    "The problems that exist in the world today cannot be solved by the level of thinking that created them."

  5. #5
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    Re: Water Pipe Bonding

    Cripple, what would be the source energizing this interior piping system that would require a conductor sized by 250.66 to clear it?

    Why can't we use a conductor sized by 250.122?

  6. #6
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    Re: Water Pipe Bonding

    charlie b, the only reason that I bond to the water pipes is for safety reasons and it's the code. Accidential contact with a hot wire in the house would fault the circuit. Again I also bond to the duct system in the house.
    Jim

  7. #7
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    Re: Water Pipe Bonding

    Originally posted by bphgravity:
    Based on the wording, a 200A home could have only 2 ground rods connected by #6 as the grounding electrode system and then have a #4 water bond?
    That's exactly what we do for a 200-amp service.


    Originally posted by iwire:
    Cripple, what would be the source energizing this interior piping system that would require a conductor sized by 250.66 to clear it?
    Apparently, the service itself, or perhaps (left over from all-metal water service systems) hot plumbing brought into the premesis from a pipe-fault nearby.

    We must assume that code requirement have evolved over the years in an attempt to keep up with changing conditions and events, like stop signs and traffic lights.

    We now know which intersections will require lights as we build them, but they had to be invented as a result of need, just like the NEC. We know about electrical fires and electrocution now, but not always.
    Code references based on 2005 NEC
    Larry B. Fine
    Master Electrician
    Electrical Contractor
    Richmond, VA

  8. #8
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    Re: Water Pipe Bonding

    So now I have a 400A service fed with 600-kcmil conductors. The grounding electrode is the concrete-encased rebar and is connected with the max required #4. There are no other electrodes present. This same structure has structural steel and interior metal water piping.

    These now are both bonded with 1/0 copper to the same concrete encased electrode as required and permitted by 250.104(A)(1) and 250.104(C).

    Can someone explain the logic of this?
    Bryan P. Holland, MCP

  9. #9
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    Re: Water Pipe Bonding

    We had somebody, dear old Bennie, he is missed.
    85deg. an Sunny today.

  10. #10
    Join Date
    Jan 2005
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    909

    Re: Water Pipe Bonding

    look at 250.104 (A) (2), in a multiple occupancy
    building, it can be sized in accordance with 250.122, so a single family home would have to have the water pipe bond sized in accordance with 250.66 but a multiple occupancy can be sized in accordance with 250.122, whats the difference.

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