Fitting sockets/switches to plasterboard wall

Discussion in 'Electricians' Talk' started by GBH, Nov 27, 2003.

  1. GBH

    GBH New Member

    Hi, (sorry, it's a bit verbose for my first posting!)

    I'm in the process of re-wiring part of my flat, specifically I'm putting in 3 new rings (one for the coumpter room 2 for the kitchen) and I have a "problem" which may not be a problem at all.

    At one end of the kitchen I have a plasterboard partition wall that seperates the kitchen from the bathroom. I've had to replace this due to damp/water damage from a badly sealed bath. So far so good.

    Part of the new kitchen I'm putting in is going to be against this wall where there was nothing before. This includes 2 double plugs and moving the current pull chord light switch behind the door to a dimmer switch in this wall for the halogens I'm putting in.

    Now I'm slightly concerned about there being a bath and shower less than 100mm away from all this electricity - albeit behind this wall. I've even gone so far as to use cement board on the bathroom/shower side to give it better moisture repellant capabilities. The plasterboard on the kitchen side will be skim plastered and on the bathroom side will be tiled to waist height then plaster to the roof.

    Does this cause a risk? I suspect not but as a DIY person taking on his first leccy job I have a VERY healthy respect for all things electrical.

    Also just a small sanity check on my calculations. Even though I have 2 rings in the kitchen the calculations are implying I need 4mm cable not 2.5mm on the rings. I suspect it's my dud calculations as almost everything I read says 2.5mm is fine for rings even when using only 1 in a kitchen. I've already split all the sockets equally on different rings and I've split the DW/Cooker (combined 4700w) onto one ring and the WM/TD (combined 4900 watt) onto another each connected via 13a dp spurs. As it's rare I'll use each pair at the same time does this sound sensible? The wires are going to be embedded in plaster from the cu with short runs through ceiling space and the afore mentioned partition wall.

    Before I actually go to do it I will sit down and work it all out exactly of course but I suspect I'm being overly paranoid!

    Any help would be appreciated.

    G
     
  2. Sparkyman

    Sparkyman New Member

    Your cables in the plater pale partion wall are fin in respect of your bathroom but I don't see why you need 2-ring mains for the kitchen and not in 4mm2 T/E. you should only need 1-ring and done in 2.5mm2 T/E.

    What is DW,WM and TD?
     
  3. Sparkyman

    Sparkyman New Member

    Plaster plate partion that is .... need to start using the spell checker I think!
     
  4. wowbagger

    wowbagger New Member

    What is DW,WM and TD?

    At a guess, dishwasher, washing machine and tumble drier.
     
  5. GBH

    GBH New Member

    Wowbagger is right, WM = washing machine, TD = tumble drier and DW = Dishwasher.

    Surely with the amount of electrical items there are these days (in my kitchen e.g. there will be toaster, fridge freezer, washing machine, tumble drier, cooker, dishwasher, kettle, blender off the top of my head) that running even 2 of the high load items like TD (2900w) and Cooker (2200 w) and at the same time for over an hour (not unreasonable) will be pushing the current capacity of a 2.5mm cable. Am I reading the calculation wrong? Add to that the fact I'm passing through the partition wall (read insulation), at least 2 cables bundled (possibly 3) and over 30m in the loop and, as I said the calculations are implying I need a 4mm cable. The more I read the more I think doing them in 2.5mm will be more than enough but I thought I'd ask the people who know :)

    Thanks for the replies

    G
     
  6. supersparky

    supersparky New Member

    run the cooker on its own circuit, it may not be pulling much at the moment but you dont want to be messing about in the future do you? and one ring will be fine, i have never herd of anyone overloading a dedicated kitchen ring.

    BR
     
  7. Earthman

    Earthman New Member

    Put cooker on its own radial - plan ahead and make it 6mm in case you want to add electric hob in future. I assume it's just an electric oven at the moment. Next remember a ring cable takes twice the current of radial - half down each leg of the ring so 30m of ring main can safely take a total of 40A or more: 20A down each leg. That's why you use a 32A mcb for a ring and 20A for a 2.5mm radial. The 32A mcb is to protect the cable. A 32A mcb is designed to trip at about 1.5 times its value, so it is designed to allow about 45A (22.5 down each side) or so before it trips.
     
  8. supersparky

    supersparky New Member

    its a little more complicated than that,
    1)the demand is very unlikly to be dead centre of the ring, so one leg will take more than the other.
    2)a type b mcb has a multiple of 5, so a 32amp device of b type will operate in 0.1seconds to 12seconds at a current of 5 * 32amp = 160amp
    a 32amp breaker carrying 40amp will trip within 1 hour as a requirement of BS EN 60898

    BR
     
  9. Earthman

    Earthman New Member

    yeah i know, but i wanted to keep it simple - GBH: if you're not following this then strongly recommend you get prof. help.
     
  10. Earthman

    Earthman New Member

  11. GBH

    GBH New Member

    Hi,

    Many thanks for the answers and I'm following it all fine. I've read through the regs, I've read many websites, diy books and pamphlets of it all but just needed a guiding hand which is exactly what you've given me. I may not have been able to articulate it all very well (or even come across as if I have some clue!) but I'm technical in my day job so I'm not scared of learning it all.

    I've been through the tlc-direct website tech area 3 or 4 times and, bizarrely enough, I ordered the book today (in case the answers were not forthcoming here)

    I've ummed and ahhhhd about putting in a dedicated radial for the cooker. If I don't need to run 2 rings into the kitchen I'll just sink the channels as planned and run an extra 6mm radial instead. Reducing my work is good :)

    Again many thanks to you all for the help, much appreciated.

    If I remember I'll drop a note back here once the sparky's been and ok'd it to tell you how it went.

    G
     
  12. Earthman

    Earthman New Member

    Hi,

    Many thanks for the answers and I'm following it all
    fine. I've read through the regs, I've read many
    websites, diy books and pamphlets of it all but just
    needed a guiding hand which is exactly what you've
    given me. I may not have been able to articulate it
    all very well (or even come across as if I have some
    clue!) but I'm technical in my day job so I'm not
    scared of learning it all.

    I've been through the tlc-direct website tech area 3
    or 4 times and, bizarrely enough, I ordered the book
    today (in case the answers were not forthcoming
    here)


    Good on'ya. I think you'll find most of us are only too willing to help someone who's prepared to put in the effort themselves as well. Let us know how it goes.
     

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