bonding/grounding and pex

Discussion in 'Plumbing Forum, Professional & DIY Advice, Tips & ' started by peltaz, Oct 22, 2009.

  1. peltaz

    peltaz New Member

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    I have been reading some of the posts about grounding after installing pex. If an existing galvanized system were grounded to the cold water main where it enters the house couldn't the old galvanized conceivably remain grounded via a jumper? If the old galvanized system were left in place and a new pex system installed around it couldn't a jumper wire serve to connect the remaining galvanized system back to the cold water main keeping the original ground intact?
  2. Lakee911

    Lakee911 I&C Engineer (mostly WWTP)

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    Location:
    Columbus, OH
    I think you're mixing up some terminology here.

    Article 100 of the NEC defines grounding as, "Establishing a connection, whether intentional or accidental, between an electrical circuit or equipment and the earth or to some conducting body that serves in place of the earth." Grounding provides a path for conducting electrical energy to earth to prevent arcing, heating, or explosion during a lightning strike.

    The NEC defines bonding as, "The permanent joining of metallic parts to form an electrically conductive path that ensures electrical continuity and the capacity to conduct safely any current likely to be imposed." As it relates to a communications system, the primary purpose of bonding is to equalize ground potential of, and eliminate static discharge between, equipment. If a potential difference exists between two objects connected by a conductor, electrons will flow along the conductor from the negatively charged object to the positively charged object, damaging electronics in its path. The flow of electrons happens until the two charged objects are equalized and the potential difference no longer exists.

    Other than that, I can't really be sure what you are asking.

    You say, "if an existing galvanized system were grounded to the cold water main where it enters the house couldn't the old galvanized conceivably remain grounded via a jumper?" For one, I think you mean bonded. Second, I don't know how the "old galvanized" and the "cold water main" differ.

    The NEC requires the cold water main, as you call it, to be bonded within 5' of the entrance into the building. If it's not metallic, no bonding. After that point if it transitions back to metallic, I don't think that isolated portion needs to be bonded.


    Jason
  3. hj

    hj Moderator & Master Plumber Staff Member

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    grounding

    If it is not metallic, our electrical panel boxes have to be labeled "Non metallic water service pipe" and a substitute ground path/method used in place to the plumbing system.
  4. peltaz

    peltaz New Member

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    Let's say that one foot of galvanized pipe in a galvanized plumbing system is removed. The previous system was bonded through the water service entrance. Once that one foot of galvanized pipe is removed the system is no longer bonded. Isn't the solution as simple as running a jumper to bridge the gap where the galvanized sections are now separated?
  5. Lakee911

    Lakee911 I&C Engineer (mostly WWTP)

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    Location:
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    It must be bonded with 5' of the entrance into the building per the NEC. If you remove that said one foot section before it is bonded, then yes you would need a jumper. If that said one foot section is after it's bonded (over 5' from the enterance), the no jumper needed.
  6. Lakee911

    Lakee911 I&C Engineer (mostly WWTP)

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    Location:
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    Why would that need to be labeled? Local code?
  7. peltaz

    peltaz New Member

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    Thanks. I have filed you away for my future engineering questions for you may have noticed that I am not one.
  8. cacher_chick

    cacher_chick Test, Don't Guess!

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    For clarification, would it not be proper to bond both sides of such a non-metallic union?

    Is the purpose of bonding to the plumbing system not to cause an overload, resulting in a tripped circuit breaker in the case of an energized conductor contacting a metallic pipe system?
  9. loafer

    loafer Mechanical Engineer

    Messages:
    49
    Location:
    Maine
    Bonding is providing a low resistance path of all metal that could become energized back to the service entrance neutral. This is why the ground and neutral are tied together at the service entrance. If a low resistance path is not established and any metal becomes energized with a “hot” wire there is risk of electrocution to anyone who touches that metal and creates a path, through the ground, back to the service entrance.

    Any metal piping. plumbing, conduit, etc. must have a low resistance path back to the neutral bus.
    Last edited: Oct 23, 2009
  10. hj

    hj Moderator & Master Plumber Staff Member

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    Location:
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    ground

    It is required because many, but not all of our service lines are copper and the label is required so any one working on the system knows that grounding to the water piping may not be adequate. I once removed an electric hot water heater. When I disconnected the cold union an arc shot across between the two halves, and everything in the house that was turned on burned out. An inspection by the city inspector revealed that the utility's neutral had failed, so the plumbing system was providing the neutral until I broke the union and converted the entire system to 240 volts. In addition, the "wire" to the ground stake was a piece of BX outer sheathing which had rusted off so it also failed.

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