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Reducing earth wires

Discussion in 'Electrics UK' started by dolph, 22 May 2008.

  1. dolph

    dolph

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    I am redoing bedroom. There will be three seperate light circuits, controlled by 1 gang 3 switches on either side of bed. (two way/three way so when her indoors is asleep I can turn off lights from my side!)

    I intend running existing light circuit to junction box (original) in loft, giving me live, neutral, earth and having a further two junction boxes adjacent which will take switched lives from bedroom switches and neutral, earth from original junction box, to connect to actual lights.

    In the bedroom switches I will have several cables running into them including an abundance of earth wires.

    As the earth wires will be interconnected up in the loft is it acceptable to just use one in the switches to connect to actual switch earth terminal and then on to metal box.

    This will save me that awful congestion inside the switches when trying to finish off.
     
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  3. Veglen

    Veglen

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    Have I read this right. You intend to have a three gang two way switch in a single back box at each side of the bed to switch three lights.

    If so why not use a deeper back box for all the cables!

    All the earths do require termination in to the back box. So unfortunately you can not do away with all those pesky earth wires!

    V

    Just out of interest how are planing to wire the switches?
     
  4. dolph

    dolph

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    Thanks for the quick reply, I do appreciate your time and effort. I am not an electrician but have done DIY electrics for many years. (I had it all signed off by a fully qualified sparkie 3 months ago when he replaced fuse board - even commenting how neat and correct my work was! ) I take ages but follow the "book" to the letter but admit I was really chuffed.

    As regards my wiring planning it is quite straightforward.

    Junction box 1 : Four terminals. Incoming twin and earth from existing lighting circuit. Outgoing twin and earth to switch, brown live, blue (sleeved brown) return from switch as switched live. Normal switched live and neutral and earth to lights. Separate earth and neutral to junction boxes 2 and 3.

    Juntion Boxes 2 & 3 : Incoming Earth and neutral from Junction Box 1, plus twin and earth from switch, the brown goes to Junction box 2 as switched live and the blue (sleeved brown) goes to Junction box 3 as switched live. Outgoing twins and earths to lights.

    Bedroom switches : No 1, live in, connected to the other two live terminals,three switched lives out. Two way wiring out to other switch from two of the three terminals, third just "yellow cable" to other switch. Twin and earth out to intermediate switch by door which returns as twin and earth to other switch which with the "yellow" cable makes the three way circuit.

    Bedroom switch No 2; Incoming just "yellow", 2 two way cables and twin and earth from intermediate switch.

    My original question re earth was that all these different cables have earth wires in them but they all come from a sngle source so whilst I would always follow regs from a commonsense angle why connect some 7/8 pieces of earth wire to basically one terminal, what extra protection does this give.

    I take your valid point re the very deepest boxes, yes I did instal these from the outset as originally I knew that all earths must be contained but thought afterwards could I get round this!

    Does this all make sense to you. If you are wondering why the junction boxes in the loft, as I said I take my time (retired) and there will be several different ceiling lights emanating from them, which I can fit and wire up before connecting to the appropriate junction boxes, at the same time keeping the existing bedroom lights in operation.
     
  5. holmslaw

    holmslaw

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  6. Veglen

    Veglen

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    Hi dolph,

    I understand you questioning the amount of earth connections considering, as you say, they will all be connected back to the MET anyway! Unfortunately, if you use Twin & Earth and 3 Core cable then the earth conductors incorporated in the cable should be terminated correctly. i.e to an earthing terminal if provided or some other suitable way of termination if supplying class 2 equip.

    Using a combination of Twin & Earth and 3 Core cables I too get 3 earths in one back box and 4 in the other! Not forgetting the 2 in the intermediate switch.

    You could always consider the use of single double insulated cables for the strappers and switch wires. Using a combination of Twin & Earth and double insulated singles you could reduce this to 1 earth in each!

    Fair point! IMO probably none, but if you don’t need them then why use this type of cable. IMHO and don't take this the wrong way. I suspect it’s all down to the circuit design!

    V
     
  7. dolph

    dolph

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    Hi Veglen

    Thanks for the advice, the single wires as you suggest not only cut down the earth wiring but will go far more easily through the conduit!

    As regards the circuit design I cannot see how it can be different as I am only using one live wire and 3 switched live wires. The 3 core is a two way convenience so that all lighting can be switched off from either side of bed, its an age thing! The two/three way circuits are as outlined in "how to do it" on this site and I have used them several times without any problems.

    As regards Holmslaw's query "what are you trying to achieve" I cannot see how I can explain it more succinctly, what dont you understand? It is two 2 way switches circuits plus one 3 way switches circuit.
     
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  9. 333rocky333

    333rocky333

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    If there is a earth in the cable , I would connect it.
    If done at both ends, it is more likely continuity is maintained if one end did come adrift.
    If the cable ever got severed or damaged for some reason, it may short to earth, isolate the circuit due to eebads and possibly prevent more damage or even a fire.

    You could use a deeper box or a double box size, 3 gang switch.
    Terminate the 8 or so wires in a 30 amp connecter block inside the box and use a 1.5 g/y link from that to the switch and to the box.
     
  10. Veglen

    Veglen

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    Hi dolph,

    I wasn't suggesting your circuit design was incorrect.

    I was only pionting out alternatives. I was trying say rather than use all earth incorperated cables like 3 core and twin & Earth, you could consider the use of single double insulated cables too.

    Providing you have an earth connection to each metal back box by using either a single 3 core cable or a twin & earth cable, the circuit would be protected. No need for all the other earths! Therefore single double insulated cables could be used for strappers between switches and switch wires. Consideration of cables to be used would be part of your circuit design.

    As you say, if you are using conduit it will also be easier to pull singles though. Although if steel conduit is used this should be earthed too!

    Good luck with the install.

    V

    editted: to say there are single core double insulatated cables available that incorperate an earth cable too!
     
  11. Taylortwocities

    Taylortwocities

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    The "earth" wire in a multicore cable is known as the circuit protective conductor. Its main purpose is to join together all exposed conductive parts and connect them to the main earthing terminal.

    In a multicore cable (eg twin and earth) it also provides a path for fault current to earth if there is (eg) damage to the cable. For this reason these conductors must be connected to earth.
     
  12. dolph

    dolph

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    Guys many thanks to you all, I thought the plumbers were superb but you are up there with them, brilliant.

    Dolph
     
  13. Space cat

    Space cat

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    Lighting circuits can suffer from unwanted capacitive coupling between live and switched live cores which, if it's big enough, can cause low energy lights to flicker. :confused: :confused: :confused: (This forum has many examples.) An earth wire between the live core and the switched live(s) will shunt the leakage away to earth ---- BUT ONLY IF YOU EARTH IT. :) :) :)
     
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