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Shock Likelihood at Switch.

Zoomup
Mornin' All,


I have just inspected and tested a renovated  old flat's wiring. The original lighting wiring in places has no circuit protective conductor. The owner has installed metal plate light switches to two positions with wooden back boxes. At these two positions there is no circuit protective conductor. The flat has a new R.C.B.O. consumer unit and all other wiring is good.


I have recommended that the switches have a C.P.C. installed (difficult and disruptive) or be changed to all insulated types.


Just what is the shock risk at these two switch positions? What is the likelihood of the metal plates becoming live due to a fault? Has anyone every seen a metal plate switch break down so that the plates becomes live?


Thanks,


Z.

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    Zoom


    I just checked the ESF guidance on un-earthed Class 1 fittings and their guidance is C2 and an unstatisfactory report.
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    I would have to agree. Unless the switch was clearly marked as “Class II”, it would be a Code C2 and “unsatisfactory” or in the old way of doing things, “Fail”. The EICR needs to reflect the installation as you found it on the day, not how it may be after a while if the householder can be bothered swapping the shiny new metal switches for some less shiny plastic ones. 


    Regards,


    Alan.
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    perspicacious:

    ...... But it could happen............ There was some time ago a comparison between the likelihood of getting 4, 5, 6 numbers correlated with loss of limbs, sight etc. Not good reading.




    Nobody who plays the Lottery with a serious hope of winning would ever fly in an aeroplane, or even (much worse) have a surgical operation. Of course in the last case, the hope of a cure (of something life-threatening rather than just inconvenient) balances the risk.


    Has anybody ever correlated the risk of shock with the cost of reducing the risk? I suspect not.


    I suspect that most people wouldn't want to get involved in electrickery because they would perceive the risk as being high. However, if their lights come on, their heaters heat, and their motors go round and round, they don't give a moment's consideration as to whether the installation is actually safe.


    ETA, at Christmas I was thanked for installing the new wall lights in the sitting room. They do indeed look good and shed plenty of light where it is needed, but my motivation for doing the work was to keep my daughter and family safe. The rewire continues and for the most part, except for the new wooden switches, you wouldn't know that anything had been done.

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    The fuse board has been replaced with a new consumer unit with RCBOs, we have not been told when and if it was replaced as part of the current upgrade.


    The installation certificate should say that the lack of a CPC is a non-compliance, to quote the ESF Best practice guide I linked to above:


    10.9. On completion of the work a record of any non-compliances, including the lack of protective conductors on the lighting circuits, must made in the Comments on existing installation section of the electrical installation certificate issued to cover the work


    So the issue should have already been documented.


    Andy B.
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    Forget Electrical Safety First. B.S. 7671 rules. The two metal plate light switches with insulated plastic rocker switches comply with 416.1 with basic insulation. The back boxes are wooden. Live parts will only become visible due to destruction of the light switch. I have told the owner of the flat that the light switches need earthing or replacing with all insulated types. The ball is now in his court as far as I am concerned. Just how dangerous is a plastic switch mounted on a metal plate in a wooden back box?


    Although 415.1.2 says that we should not rely on an R.C.D. for sole means of protection, in this case there are two stages to a possible shock. 1. Failure of basic insulation (very unlikely) if the switch falls to pieces nobody will want to touch it, and earthing will not help anyway, and 2. Failure of the R.C.D. 


    Just how dangerous is an M.C.B. mounted in a metal cased consumer unit on a T.T. earthed supply system? This is a similar situation. Partially earthed metalwork and basic insulation of the M.C.B. You don't worry about that do you. (Well I do, and install an upstream R.C.D. to the consumer unit).


    Z.


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    We all know how much consideration a consumer faced with remedial work will give it............



     




    No we don't. 


    Z.

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     The EICR needs to reflect the installation as you found it on the day, 




    It was.


    Z.

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    Zoomup:




    Satisfactory." adjective. Acceptable, but not outstanding or perfect. 

    Compact Oxford English Dictionary.

    Z.




    And the definition to the relevant BS?


    Jaymack
  • 0
    Good for you Zoom in sticking to your guns. ESF can only provide guidance on appropriate codes, they obviously did not review your individual situation so are not in a position to exercise engineering skill and judgement on it. However, in arriving at a decision on risk HSE will advise that relevant technical guidance including manufacturers instructions should be taken in to account. The absence of fundamental control measures, irrespective of assessed risk would have led me apply a code 2 or to hold the EICR until the switches were replaced. But that is just my opinion. 

    Interestingly, we failed to get in to the NICEIC on our first attempt 35 years ago because of such a situation. Stupidly we had wired a 2-way lighting circuit without bringing a cpc to the switch. Nice brass accessories were fitted. Everything was going well and we were on schedule for a positive outcome. We were just about to leave the property when the inspecting engineer noticed the switches were brass and decided to do a wander lead check. Deservedly, down the plug hole we went!  Ever since I insisted that we used single core and earth whether needed or not! 

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    You actually have a guide as to whether an earth is required or not and that is the presence of an earth terminal on the accessory itself. Many of these "metal" switches and sockets simply have a metal cover over a conventional plastic accessory, and there is no requirement to earth this extraneous part as the chance of a connection to it is probably zero. A solid brass accessory is rather different. Of course a quick meter check will provide useful information too.

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