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practical need for supp bonding in bathroom

wallywombat
Can anyone suggest a realistic scenario where supplementary bonding would be required in a bathroom or other 701 location? I'm failing to think of one, although I may be overlooking something blindingly obvious.


It can be omitted as long all three of these are satisfied: ADS in time; RCD present; any extr-c-p connected to main bonding.


If ADS can't be done in time by either MCB/RCD then its not legal anyway.

RCD has to be present anyway.

Water and gas pipes etc should already be main bonded if they introduce a potential.
  • 0
    What you are asking is "Is supplementary bonding ever required where no supplementary bonding is required?".


    The answer is obviously "No".


    However, there are still many installations where the three conditions (for omission) are not met; usually a lack of RCDs.
  • 0

    However, there are still many installations where the three conditions (for omission) are not met; usually a lack of RCDs.




    I don't follow. 701.411.3.3 requires RCD protection for the circuits in the bathroom. Then 701.415.2 (v) says that you can omit bonding if (amongst other things) RCDs are present. Or are you saying that for existing installations which don't have an RCD on the relevant circuits, then its ok to modify the circuit without adding an RCD, but you must add supplementary bonding???

  • 0
    Customer's preference?


    Effectively obsolete for new work, but consider the situation in which an EICR identifies absence of both supplementary bonding and RCD in the case of extraneous CPs.


    Options are to bond (subject to the caveats above) or to put an RCD in the circuit. Quotes provided. Customer chooses the cheaper option of bonding.
  • 0
    Before we get too hung up about existing installations, let's consider just a new build to 18th Ed. Is there a scenario which is fully 18th compliant and which requires supp bonding?
  • 0

    wallywombat:

    Before we get too hung up about existing installations, let's consider just a new build to 18th Ed. Is there a scenario which is fully 18th compliant and which requires supp bonding?




    No, but the regulations do not just consider new-builds. They also apply to the majority of installations which are not new-builds.


    You might as well say that all new builds have plastic water services so why do the regulations still mention main bonding a metal water service.

  • 0

    wallywombat:



    I don't follow. 701.411.3.3 requires RCD protection for the circuits in the bathroom. Then 701.415.2 (v) says that you can omit bonding if (amongst other things) RCDs are present. Or are you saying that for existing installations which don't have an RCD on the relevant circuits, then its ok to modify the circuit without adding an RCD, but you must add supplementary bonding???


    Depending on what your modifications entail, you might not have to add an RCD to that circuit and definitely not to any other circuits.


    The supplementary bonding should already be there, shouldn't it? You can check and if not, fit it.



    Have you been telling your customers that new consumer units are compulsory before any other work can be carried out?
  • 0
    " Before we get too hung up about existing installations, let's consider just a new build to 18th Ed. Is there a scenario which is fully 18th compliant and which requires supp bonding? "

    yes for an 18th edition  rewire in an building of unknown vintage.

    The effectiveness of the connection of extraneous-conductive-parts in the location to the main earthing terminal may

    be assessed, where necessary, by the appication of Regulation 415.2.2.




    and then




    415.2.2 The resistance R between simultaneously accessible exposed-conductive-parts and extraneous conductive parts shall fulfil the following condition:

    R <50 V/Ia in AC systems... where Ia is the operating current in amperes (A) of the protective device or:

    (i) for RCDs, Ian

    (ii) for overcurrent devices, the 5 s operating current.






    Not unknown for items like a cast iron soil stack, or existing metal radiators, to be not really as well bonded back to the MET as this requires, and at the same time not well enough isolated from ground to be truly considered not to be an extraneous part.

    In such a case a local bond solves the issue.

     


  • 0

    Water and gas pipes etc should already be main bonded if they introduce a potential.



    Ah, but what are extraneous-conductive-parts as far as the installation is concerned aren't necessarily the same as what are extraneous-conductive-parts as far as the bathroom is concerned. Take the classic plumbing setup for hot water - copper cylinder in a cupboard somewhere (possibly in the 2nd bedroom), fed from a plastic cistern in the loft, and an immersion heater fed from an old 15A rewireable fuse with anything up to 5s disconnection time. The hot water pipes aren't effectively connected to the main bonding because of the plastic cistern in the loft - which is of itself fine as the hot water pipework can't introduce a potential into the installation -  but because it's effectively an extension of the immersion heater's c.p.c. it the can introduce a potential into the bathroom. A fault on the immersion heater side-steps all the RCD protection for the bathroom circuits and puts a possibly lethal potential between the hot tap and the (main bonded) cold tap for possibly a lethal duration. You choices then are either to main bond the hot water pipework or supplementary bond everything within the bathroom. (Adding 30mA RCD protection to the immersion circuit might also work, but isn't recognised by the regs as a solution - possibly because of the risk of picking up similar potentials due to faults elsewhere in the installation.)


      - Andy.
  • 0
    Thanks guys, makes sense now.
  • Former Community Member
    0 Former Community Member
    I am working on a freestanding double garage  being converted to a small flat at the moment. Water comes into the building in plastic, there is no gas, so the mains services are not bonded. Has its own dedicated PME supply.  Water is distributed above the bathroom in plastic but the owner wants chromed copper downpipes from the loft space. In the bathroom there will be;

    A sink with cold water tap fed by an exposed chrome pipe.

    An 3 kW hot water hand wash above the sink, exposed chrome pipe.

    An 60w oil filled electric towel radiator.

    A 600w macerator.

    A loo with cold water exposed chrome pipe inlet.

    An extractor fan.

    A 9.5 kW shower fed by an exposed chrome pipe.

    A very nice IP rated LED light.


    Its very tight in there and much of it can be simultaneously touched.   Disconnection times are no problem and all circuits are either an RCD or RCBO.  I believe the whole lot needs bonding, am I right ?

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