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Thread: Equipotential Grid

  1. #1
    Join Date
    Sep 2008
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    1

    Equipotential Grid

    Does the grid comprising the equipotential grid, in this case #3 schedule 60 rebar need concrete cover or lay on the ground? when this rebar rusts, being bonded to the pool rebar it will in turn pass this potential and the pool rebar will rust. I can't find a code reference.

  2. #2
    Join Date
    Jan 2008
    Location
    Washington State
    Posts
    141
    2005 NEC 680.26(C) and here is Washington State take on the issue.

    NEC 680.26(C) describes the specific requirements for the equipotential bonding grid for pools with
    paved walking areas (e.g. concrete, tiles, pavers, wood, etc.). The grid must extend from the inside walls
    of the pool at least 3’ under the walking area. Depending on the type of pool construction, you have three
    options for constructing a grid under the walking area:
    Structural reinforcing steel – This option can only be used with a steel reinforced concrete pool.
    Uninsulated steel structural reinforcing bars may be used to make a grid if they are bonded together with
    steel tie wire or equivalent.
    Bolted/welded metal pools – The wall of a bolted or welded metal pool may be used as the grid.
    Alternate means – This option can be used when a deck media exists (e.g. concrete, pavers, wood deck,
    etc.). The grid must be made of a minimum #8 solid copper conductor that is bonded at all crossing
    points. The grid must cover the entire area from the contour of the pool and extending at least 3’ under
    the pool deck. The grid must be made in a 1’ x 1’ perpendicular pattern ± 4”. The grid must be secured
    within or under the pool and deck media.
    The 2005 NEC does not have specific grid installation methods for a pool with no paved walking area
    (e.g. grass, gravel, etc.). The lack of description does not eliminate the requirement for a grid. For the
    perimeter area around these pools, L&I inspectors will accept a single, minimum #8 solid copper,
    conductor that is installed between 18” and 24” of the contour of the inside wall of the pool and is buried
    under the perimeter surface at least 6” below grade. Only listed splices will be accepted.
    All metal parts requiring bonding in NEC 680.26(B) must be bonded to the equipotential bonding grid.
    The 2008 NEC modifies some of these requirements. They will be covered in a future newsletter

    As my boss says "It is all black and white."

    But IMO the exposed rebar is no good.

  3. #3
    Join Date
    Mar 2004
    Location
    Arizona
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    Nice job MisterMudd !!!!
    Frank Arizona,USA

  4. #4
    Join Date
    Jul 2008
    Location
    Michigan
    Posts
    1,904

    Smile

    I wish all states would provide amews letter like that.

  5. #5
    Join Date
    Jun 2008
    Posts
    2

    Equipotential Grid

    The NEC 2005, 2008 editions do not offer any directions for steel reinforcing bars that comprise the equipotential grid in relation to earth seperation. The 2008 NEC states that these steel reinforcing bars if encapsulated are not required to be bonded. So when these rebars are placed on soil or earth they rust. This rust is an electrochemical reaction that travels down the rebar to other rebar connections. Since this is now in turn bonded with a minimum #8 copper conductor this potential is passed to the sturctural rebar of the pool. The gunite cracks from the expansion of the rusting rebar and the pool eventually falls apart. All because no minimum is given for protection of steel rebar in the equipotential grid. Sure it seems like a good idea to require coverage but we don't design we enforce the code. If the code is silent so is the requirement. It's a bad deal that needs a simple code fix in the text.:-?

  6. #6
    Join Date
    Mar 2004
    Posts
    590
    Quote Originally Posted by MUrry
    The NEC 2005, 2008 editions do not offer any directions for steel reinforcing bars that comprise the equipotential grid in relation to earth seperation. The 2008 NEC states that these steel reinforcing bars if encapsulated are not required to be bonded. So when these rebars are placed on soil or earth they rust. This rust is an electrochemical reaction that travels down the rebar to other rebar connections. Since this is now in turn bonded with a minimum #8 copper conductor this potential is passed to the sturctural rebar of the pool. The gunite cracks from the expansion of the rusting rebar and the pool eventually falls apart. All because no minimum is given for protection of steel rebar in the equipotential grid. Sure it seems like a good idea to require coverage but we don't design we enforce the code. If the code is silent so is the requirement. It's a bad deal that needs a simple code fix in the text.:-?
    I don't know if I buy the bit about rusting rebar putting a potential on the pool rebar. I do think it odd that you would consider constructing an equipotential grounding grid out of something that will rust away in a short time, leaving you with no grid. Why would you put steel rebar in the ground without it being in concrete?

  7. #7

    brick at edge of pool

    saw a pool today a layer of brick around the pool wall " bull dog " then 3' gride
    pool co. is trying to fall back on the idea that re bar under brick is a grid

  8. #8
    Join Date
    Mar 2004
    Location
    Arizona
    Posts
    3,913
    Quote Originally Posted by mh183
    saw a pool today a layer of brick around the pool wall " bull dog " then 3' gride
    pool co. is trying to fall back on the idea that re bar under brick is a grid
    680.26(C)(1) NEC 2005,
    Frank Arizona,USA

  9. #9
    yes but someone is not going to be happy today

  10. #10
    Join Date
    Mar 2004
    Posts
    590
    I think the confusion may be the term "encapsulated". "Encapsulated in a nonconductive compound" means non-conductive coated (like PVC) steel rebar, not rebar embedded in concrete. See http://www.mikeholt.com/videodisplay.php?id=74

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