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Special Locations Pool Rebar Bonding

Steven Dwight

Hi all, in a domestic pool installation, the contractor has formed the concrete base of a swimming pool, linked to the main house, and not bonded the slab rebar. My understanding is that the contractor will now need to expose the rebar and bond back to the main earth terminal. My concern is this will affect the integrity of the pool slab (future weak spots and leaking) and also whilst trying to achieve complete rebar continuity could result in many holes. I believe there is insulation and screed going on top of the slab (I maybe wrong), could a secondary earth nest be sat on top of the slab or would this create more issues by in essence adding secondary extraneous conductive parts?

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  • +1

    I'm probably being dim ... but where has this requirement for bonding rebar come from? Unlike 705 I can't see any particular reference to rebar in 702. There is a reference to an earth mat or electrode providing a resistance of 20 Ohms or less when using PME, but there doesn't seem to be any guarantee that the rebar would achieve that (if there's a plastic sheet under the slab, it's probably quite unlikely). Is the assumption that the rebar is an extraneous-conductive-part? If it's not accessible from within the installation (either directly or via something conductive, e.g. damp concrete) is that the case here?

       - Andy. 

  • +1 in reply to AJJewsbury
    AJJewsbury said:
    There is a reference to an earth mat or electrode providing a resistance of 20 Ohms or less when using PME, but there doesn't seem to be any guarantee that the rebar would achieve that (if there's a plastic sheet under the slab, it's probably quite unlikely).

    See also G12/5. It's also commonly done for ground floor shower blocks in sports clubs etc ... and cattle sheds.

    No "firm requirement", but if there is a grid it should be bonded.

    There is no guarantee that such a grid will prevent "tingles" from diverted neutral currents - it depends on the magnitude in the area. A TT approach might be recommended where this is practicable (e.g. suitably separated outbuilding).

  • 0 in reply to AJJewsbury

    Hi Andy, thanks for your reply.

    You are correct, I am assuming that the rebar is classed as extraneous therefore requiring a link back to the main earth terminal.

    Its the damp concrete that worry's me, and how porous it may be.

    I'll need to ask the contractor if a plastic sheet has been installed as part of the slab build up, I would expect so.

    Steve

  • 0 in reply to gkenyon

    Hi Graham, thanks for your reply

    The pool forms part of the main house, one building. 

    My thoughts were to provide a 'TT' earthing system due to the proposed 2No DNO supplies into the property. (although until I speak with the DNO I'm not entirely sure if their second supply is terminating into a GRP enclosure on the site boundary).

    To provide a TT system feels like the correct method as we are then in control of a single earthing system for the entire property, not a hybrid of two earthing systems that are linked (which I'm not sure is compliant)

    Steve

  • 0 in reply to Steven Dwight
    Steven Dwight said:
    To provide a TT system feels like the correct method as we are then in control of a single earthing system for the entire property, not a hybrid of two earthing systems that are linked (which I'm not sure is compliant)

    The only thing to consider, is if extraneous-conductive-parts of the installation, particularly metallic service pipes, are shared with other installations, or whether those pipes (or earth electrodes) are installed close to metalwork connected to PME below ground. If so, you can't get away from PME.

    Does require some thought before you start work, though, because it's far more difficult when all the work is complete, to try and back-engineer the TT approach (especially if work is needed below ground to check distance of electrodes from other services/metalwork).

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  • 0 in reply to Steven Dwight
    Steven Dwight said:
    To provide a TT system feels like the correct method as we are then in control of a single earthing system for the entire property, not a hybrid of two earthing systems that are linked (which I'm not sure is compliant)

    The only thing to consider, is if extraneous-conductive-parts of the installation, particularly metallic service pipes, are shared with other installations, or whether those pipes (or earth electrodes) are installed close to metalwork connected to PME below ground. If so, you can't get away from PME.

    Does require some thought before you start work, though, because it's far more difficult when all the work is complete, to try and back-engineer the TT approach (especially if work is needed below ground to check distance of electrodes from other services/metalwork).

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