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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
    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.


Reply
  • 0
    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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