Earthing in Metal Back Boxes

Discussion in 'Builders' Talk' started by DanielQ, Aug 13, 2018.

  1. DanielQ

    DanielQ Member

    If I fit metal back boxes for light switches and sockets, do I need to connect the earth wire to the back box or the earth wire only goes to the back of the socket or switch?

    I will be installing MK sockets and switches.

    Thank you.
  2. Pollowick

    Pollowick Screwfix Select

    This will open the "can of worms again" - you will get opinions that both are correct for light switches, however for sockets, outlets, fcus and all others it must be to the accessory earth connection. For completeness, irrespective of which way you go on switches, always put a link from accessory to back box in all cases.
    KIAB likes this.
  3. DanielQ

    DanielQ Member

    Thank you for the reply.

    What's the best way of connecting the the back box to earth? short sleeved wire to the socket?
  4. DIYDave.

    DIYDave. Screwfix Select

    What type of light switches are you fitting ?

    Plastic or metal faceplates ?

    If you have any electrical places near you that sell cut cable, see if they sell ‘earth singles’ by the meter (1.5mm I think is fine ?)

    If you have several fly leads to make up then this is the easiest option and will cost pennies
  5. DanielQ

    DanielQ Member

    Plastic faceplates.

    I will search for earth singles by meter. 1.5mm is enough for ring main?
  6. DIYDave.

    DIYDave. Screwfix Select

    Plastic faceplates require no earth connection and are unlikely to have an earth tag anyway

    So your earth or CPC, (as the pros call it :)) goes direct to the lug on metal back box, sleeved of course in green and yellow

    If fitting any metal faceplates, then the earth from cable goes direct to faceplate, then an earth flylead from faceplate to back box (always generates pages of debate if required or not but.........)

    For your sockets, CPC size in 2.5mm Twin and Earth is 1.5mm I’m fairly sure so yeah, 1.5 earth singles is a good way of going (if you can purchase by the cut meter) ?

    Often used is just a length of earth stripped out the cable and sleeved

    I’m only diy me so get a definitive answer from a pro as this topic always generates loads of differing views :D Good luck !
  7. Pollowick

    Pollowick Screwfix Select

    Only on switches ... other plastic faceplates will have an earth as part of the assembly and that is likely to be continued out to form a ring around the fixing holes.
  8. DIYDave.

    DIYDave. Screwfix Select

    Yes of course :)

    Was in relation to my prev question if switches were placy or metal

    I did then go on to mention earthing sockets

    But yep, always good to make crystal clear

    How’s my advice on using 1.5 singles for switch/skt earths ?

    I found a 100m drum years ago outside a building site and have been using that ever since (will last me a lifetime at least)

    Also good as a draw wire for pulling cables through trunking and hard to get to places :)
  9. 14th edition

    14th edition Well-Known Member

    No requirement to earth the back box provided there is one metal fixed lug on the box. You earth the accessory and the fixing screw picks up the death from the fixed lug.
  10. DIYDave.

    DIYDave. Screwfix Select

    I did say in thread 6 that this topic always generates pages of debate re fly lead ....... it’s been done to death over the years

    I’m diy but you guys, ‘pro sparks’, can’t even agree on the matter, irrespective of regs

    Just easier to let people get on with adding an Earth lead if they wish, what’s the big deal :confused:
  11. Sparkielev

    Sparkielev Screwfix Select

    Noooooooooooooooooo another earthing back box thread
    KIAB likes this.
  12. Bob Rathbone

    Bob Rathbone Screwfix Select

    Let's assume that a plastic switch is being fitted, then the CPC (earth) will be connected to the terminal in the box and the box will then be earthed. Should someone change the switch to a metal plate version, then the metal plate must be earthed. The discussion is, ' how?' Some will say that the CPC should be left in the box terminal and a flylead connected between this and the switch, my preferred method, others will say move the CPC to the switch plate. My issue with the second method is that the earth connection to the back box is now fortuitous, and will be lost when the accessory fixing screws are removed or loosened. Some may disagree.

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