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Lack of visible supplementary Bonding

Hi Guys.   I looked a a job today with a 16th edition CU so no rcd on the bathroom lights.  There is no visible supplementary bonding. Lots of pipes boxed in, bath panel not removable.  I had a reading of pretty much zero ohms from the hot and cold below the sink to the radiator so suspect it is done somewhere.  However i suspect the lights are not done as i dropped the down lights out and the switch.   There is a class one shaver point over the sink although it doesn't have any exposed metal parts.  I am getting 0.25 ohms from the earth at the shaver to the sink pipes.  The bathroom is next to the CU, well it's outside the door so the cpc run is pretty short.  What sort of reading do i need to be seeing here before i don't need to worry about a supplementary bond.  Is 0.25 low enough.

Thanks

Gary

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  • R ≤ 50V/Ia - where Ia is the fault current necessary to open the associated protective device within 5s. (Reg 415.2.2)

    Picking the right device(s) to consider can be a bit tricky - it's more about thinking about the circuits that could impose a voltage on the exposed- and extraneous-conductive-parts within the bathroom rather than necessarily just the bathroom circuits. E.g. don't overlook things like an immersion heater in a bedroom that shares metallic hot water pipework with the bathroom taps.

       - Andy.

  • I presume the shaver skt is fed by the lights, and the exposed front panel screws are the only earthed part that in the event of a fault might not clear in the required 0.4 seconds ?

    0.25 ohms is still a touch under 1kA. What devices do you have in the CU that will not promptly trip at that sort of current, or even at 100A, if the answer is 'none' then the bonding is adequate.

    I suspect bonding present but maybe a bit corroded, and that if a real fault with bit of oomf came along it would re-weld into a lower impedance state.

    As there is no RCD do you have a high current loop test on your meter ? - it may give a lower reading. Or if there is a very whispy connection that would not stand a real fault, it will blow it open cct, but at least you know that it was inadequate,  before it fails to save someone.

    Mike.

  • Thanks Mike.  As far as i can see there is nothing exposed, not even screws. The cover hiding the terminals is behind the lamp and that screw goes into the plastic. The front diffuser clips on.The ends are all plastic.    Yes i can do a high current loop test.  

    Cheers

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  • Thanks Mike.  As far as i can see there is nothing exposed, not even screws. The cover hiding the terminals is behind the lamp and that screw goes into the plastic. The front diffuser clips on.The ends are all plastic.    Yes i can do a high current loop test.  

    Cheers

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