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Shock Likelihood at Switch.

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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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  • 0
    Although a metal wall switch without a cpc is a single fault to danger, I think it is mitigated by (1) there is little movement  - the switch mechanism itself moves, but the overall accessory is firm - unlike a ceiling pendant for example where someone changing a bulb or shade might cause all sorts of yanking and chafing. So for example even if a wire was loose in a terminal, it's unlikely to ever move and touch the exp-c-p. (2) Any body contact is likely brief - there's nothing to clench onto if finger muscles go into spasm, and it's relatively hard to fall onto. Unless there are factors in the other direction, I think its reasonable to argue for a C3 in those circumstances.
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  • 0
    Although a metal wall switch without a cpc is a single fault to danger, I think it is mitigated by (1) there is little movement  - the switch mechanism itself moves, but the overall accessory is firm - unlike a ceiling pendant for example where someone changing a bulb or shade might cause all sorts of yanking and chafing. So for example even if a wire was loose in a terminal, it's unlikely to ever move and touch the exp-c-p. (2) Any body contact is likely brief - there's nothing to clench onto if finger muscles go into spasm, and it's relatively hard to fall onto. Unless there are factors in the other direction, I think its reasonable to argue for a C3 in those circumstances.
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