Consumer Unit Positioning

Discussion in 'Electrics UK' started by ryanj, 1 Jun 2004.

  1. ryanj

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    During my rewire, I plan to move my consumer unit to a new position. Currently, it is in a room with a concrete floor, I propose to move it to allow me to get cables into the crawlspace easier.

    My supply is an overhead TT supply. Would it be acceptable to simply run 25mm sqr metre tails from the metre in the old position to the new consumer unit, or would I have to contact the power company to move the metre beside the consumer unit?

    Also, is it fine to have earth rods driven from the crawlspace, rather than have them taken outside? And must I use a "whole-house" RCD, if I can get the earth fault loop impedance low enough?

    And, is it acceptable to use a flush consumer unit in domestic situations, as it'd help keep everything neat?

    And, is it acceptable to run cables in the crawl space without clipping them to the joists, or running them through the joists?

    Finally, where the cables leave the consumer unit, do the cable grouping de-rating factors take effect for 1-2metres down the wall?
     
  2. plugwash

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    you aren't meant to run tails more than 3m without having your own isolation and protection

    the main rcd for a TT must be in a plastic enclosure

    you could use a plastic 4 module enclosure with the 100ma type S rcd and a 100A mcb (http://www.tlc-direct.co.uk/Products/CMDK401.html)

    then run from that to a normal split load CU preferablly using 25mm swa
     
  3. securespark

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    2m for Norweb.
     
  4. ryanj

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    Anyone else? :oops:
     
  5. il78

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    Go for what plug suggested, creating a distribution circuit, have the position where you want then.....
     
  6. ryanj

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    Thanks! Got that problem sorted out.

    Any advice on the others?
     
  7. il78

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    You can have the rod in the crawl space as long as its <100Ohms. (Make a label stating the location)

    Not to sure what you mean about the RCD, but a TT system requires that the installation is protected by an RCD usually 100mA although a 30mA is required for supplementary protection.

    Cant see a problem with using a flush mount DB

    Clip the cables in the crawl space

    Grouping factors for that amount of lenght shouldn't be a problem.
     
  8. ryanj

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    Are you sure the whole installation must be protected?

    The only thing I can find in the regulations states that all socket outlets on a TT system must be RCD protected. Nothing else.

     
  9. plugwash

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    yes but you will never meet disconnect times otherwise

    the impedcence of the earth limits the current flow down it to a value insufficint to trip a fuse or mcb

    that is why you need the main rcd
     
  10. ryanj

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    But, if i could reach required disconnection times, would I need to use a main RCD?

    Also, could I run meter tails instead of using SWA?
     
  11. plugwash

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    tails would probablly be ok but they should be protected from damage

    a worst case allowed TT is 200 ohms this will allow just over an amp to flow in the case of a short to earth (obviosuly until this fault is disconncted your entire earth system will be live so it should happen asap)

    so either a rcd is essential OR it would have to be a bloody good TT (like big mats burried below the water table)

    with a ROD you will not manage it
     
  12. ban-all-sheds

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    Particularly with a rod in a dry location - ryanj, what do you mean by the term "crawlspace"?
     
  13. ryanj

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    Crawlspace - Small area under the floorboards of the ground floor.
     
  14. plugwash

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    it would be an insanely stupid place to put a rod

    to get a usable earth the rod needs to be at least partially in wet soil
     
  15. ryanj

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    Fine, I'll use multiple earth rods in the back garden to try and keep the resistance low.
     

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