using copper waterlines under slab for additional ground ?

Discussion in 'Electrical Forum discussion & Blog' started by bullet, Mar 25, 2013.

  1. bullet

    bullet Guest

    would like to add another ground to main panel, have plastic waterline to house[from well] the water lines underslab branch out to kitchen and bath, and to outside faucet, about 60' of copper lines altogether , all lines are in contact with the ground UNDER the 4" concrete slab,, could a ground wire from main panel be attached to copper lines for additional ground? thanks
  2. Terry

    Terry Administrator Staff Member

    Messages:
    15,130
    Location:
    Bothell, Washington
    Normally dry earth is not much help for grounding.
    Grounding rods go down deep enough that you find moist dirt.
    Often times copper lines are grounded or bonded in case a bare wire touches them.

    A panel should have two grounding rods, and not rely on the plumbing.
    Here, is we do a repipe on a home, we're required to have the panel grounded properly before we repipe.
    Years ago they would use the copper pipe for grounding. We had to leave about ten feet out of the foundation. Too many copper thieves now for that to work.
    Last edited: Mar 25, 2013
  3. cacher_chick

    cacher_chick Test, Don't Guess!

    Messages:
    3,249
    Location:
    Land of Cheese
    The question to ask is if you have the required ground rods for the electric service, what do you accomplish by connecting your piping to the existing system? You could if you wanted to, but there is no requirement to do so.
  4. Speedy Petey

    Speedy Petey Licensed Electrical Contractor

    Messages:
    996
    Location:
    NY State, USA
    I'll also ask. WHY are you doing this? Are you assuming there is some benefit?
  5. pigrew

    pigrew New Member

    Messages:
    11
    Location:
    West Lafayette, IN
    Edited: (Removed things that I wasn't completely sure about, see jwelectric's post)

    A metal water pipe system is required to be bonded to your ground. (NEC 2011: 250.104A).

    But, these pipes wouldn't count as a ground because they are not in a permanently moist part of the soil (250.53A1) since it's pretty dry beneath your slab.

    Bonding these additional items to ground will provide you with superior lightning protection (even if they are not adding any additional "grounding"). Also, bonding them will make thing safer if a live wire ever touches the pipe. If there is rebar in your footings, it would be a good idea to bond these to your ground, too.

    So, you still need two ground rods to have sufficient ground, preferably separated by 16 feet. (or some other permissible source of a ground).

    -Nathan
    Last edited: Mar 25, 2013
  6. jwelectric

    jwelectric Electrical Contractor/Instructor

    Messages:
    2,540
    Location:
    North Carolina
    There is a big difference between bonding found in 250.104 and grounding found in 250.52.

    Any time one rod is driven add the second rod unless you intend to pay an engineer to prove that one rod sustains 25 ohms or less 24/7.

    Anything under a pad will not constitute a grounding electrode as Terry pointed out, not enough moisture to do any good but if it is a complete copper piping system then it is required to be bonded. Any rebar in the pad needs nothing and will provide nothing. In order for rebar to be of any value it must be in the footer and the footer must be in contact with earth.
  7. pigrew

    pigrew New Member

    Messages:
    11
    Location:
    West Lafayette, IN
    Of course, you're right. I missed the part in 250.53 that was mentioning that it has to be in a moist part of the ground. I removed a lot of what I said in my above post.
  8. hj

    hj Moderator & Master Plumber Staff Member

    Messages:
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    Location:
    Cave Creek, Arizona
    Here, regardless of whether copper water lines are under the slab, which most are, when there is a plastic water supply line to the building, the electrical panel MUST be annotated, "Plastic water main, must have approved ground rods".
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