Rules and Guidelines
Want to participate in the discussions? Please read our Community Rules and Guidelines. Need some help? Visit Support and Answers.

  • State Not Answered
  • Locked Locked
  • Replies 102 replies
  • Subscribers 31 subscribers
  • Views 7446 views
  • Users 0 members are here
Options
You may also be interested in
This discussion is locked.
You cannot post a reply to this discussion. If you have a question start a new discussion

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.

Parents
  • 0

    perspicacious:
    Is the back of metal frontplate insulated somehow or is it exposed to the wiring within the backbox?


    Does it have the Class II symbol?


    Regards


    BOD




    I'd be more concerned with the physics of the situation rather than compliance with paper standards - after all we'd have fewer worries if the plateswitch was plastic, but as far as I'm aware they don't carry the square-in-square symbol either.


    My main concern isn't so much  a wire popping out of a terminal so much as one of the wires resting on the back of the frontplate (usually it's very difficult to be 100% sure this isn't the case as you can't see inside when the switch is pushed back into position), it then only needs a loose connection or a bad contact on the switch for the wire to overheat and the insulation to soften and so allow the copper to creep through, especially on a bend (I'm sure we've all come across examples of that from time to time).

     



    What code for a wooden back box?



    Presuming it's a proper wooden box, designed & manufactured for electrical use, and so of a type of wood that should char rather than burst into flames on a glow-wire test, I would have thought it wouldn't have been significantly more risk from a fire point of view than a PVC box meeting today's standards. So unless it was unsuitable for some other reason (damp environment perhaps), I don't think I'd code it. 

     



    8. The flat owner has been told that an improvement is necessary



    Yet you've also stated (by giving a 'Satisfactory') that the installation is suitable for continued use in its current condition - which could well give the impression to the layman that improvements aren't really necessary after all.


      - Andy.

Reply
  • 0

    perspicacious:
    Is the back of metal frontplate insulated somehow or is it exposed to the wiring within the backbox?


    Does it have the Class II symbol?


    Regards


    BOD




    I'd be more concerned with the physics of the situation rather than compliance with paper standards - after all we'd have fewer worries if the plateswitch was plastic, but as far as I'm aware they don't carry the square-in-square symbol either.


    My main concern isn't so much  a wire popping out of a terminal so much as one of the wires resting on the back of the frontplate (usually it's very difficult to be 100% sure this isn't the case as you can't see inside when the switch is pushed back into position), it then only needs a loose connection or a bad contact on the switch for the wire to overheat and the insulation to soften and so allow the copper to creep through, especially on a bend (I'm sure we've all come across examples of that from time to time).

     



    What code for a wooden back box?



    Presuming it's a proper wooden box, designed & manufactured for electrical use, and so of a type of wood that should char rather than burst into flames on a glow-wire test, I would have thought it wouldn't have been significantly more risk from a fire point of view than a PVC box meeting today's standards. So unless it was unsuitable for some other reason (damp environment perhaps), I don't think I'd code it. 

     



    8. The flat owner has been told that an improvement is necessary



    Yet you've also stated (by giving a 'Satisfactory') that the installation is suitable for continued use in its current condition - which could well give the impression to the layman that improvements aren't really necessary after all.


      - Andy.

Children
No Data

Join us to get the best from IET EngX.

Joining EngX lets you personalise your experience so you stay up to date on the topics that interest you, plus you’ll be able to make connections who are looking to collaborate, exchange ideas and more.

Join us Not now

Community Rules & Guidelines