8.5kw shower cable

Discussion in 'Electricians' Talk' started by lvlouse, May 13, 2018.

  1. lvlouse

    lvlouse New Member

    hey all,

    I’ve scoured the forums for a concrete answer and although similar questions have been asked, I struggle to feel reassured that the cable is adequate. Due to some saying yes and others saying no. So I thought i best lay out my situation and hopefully everyone can give me reasonable positive answers.

    So here’s my situation, i have arranged for our shower to be moved and replaced, I have bought a new 8.5kw shower (like for like rating wise), I have replaced and moved the pull cord, again like for like. The existing 10mm t/e from the fuse box has been reused, this would be about 10m long and in the loft travels through maybe 2m of insulation which having looked on these forums seems to be a non issue for 10mm t/e cable. Obviously I know this cable is handling the shower fine but I thought I’d lay out all the info anyway, my question is this;

    I have no 10mm cable to run the last 2m (if that) from the pull cord to the shower, I do however have 6mm cable, I know the cable is rated enough, but this 2m of cable will run entirely through the wall, over the door frame and into the shower.

    This is hooked up to a 40amp type b mcb.

    Will the 6mm cable be adequate for the use stated above?

    Thanks in advance for your help


  2. Heat

    Heat Well-Known Member

    Yes Carl, definitely 6mm cable will be fine. In fact it often will do an 8.5 kw shower entire supply.
    I actually would recommend any 8.5 or for that matter, 9 and 9.5kw showers to have the cable from the pull cord to be 6mm so to be easier to install.
    Do try to put the 6mm cable in conduit that is plenty big enough and leave extra length on the cable for the future so it can be pulled through.
    I prefer to use 50amp pull cord switches in the hope that it will be better quality contacts than the 45amp which often fail
    Last edited: May 14, 2018
  3. lvlouse

    lvlouse New Member

    thanks for your answer, very much appreciated.

    You mention about putting the cable in conduit, i feel like i've not been clear enough when i said 'through the wall', by this i meant it will enter the wall through a 20mm hole in what i beleive is called the top plate (accessed via the loft), then through 4 studs (again, 20mm holes) and exit the wall through a hole behind the shower unit. Also, the path the 6mm cable would take is not insulated.

    will this still be ok?


  4. JP.

    JP. Screwfix Select

    You have a nice run of 10mm going to the pull cord switch (Crabtree is best) - why not do the last 2 metres from the pull cord in 10mm and not 6mm Ivl?
    Josh.91 likes this.
  5. Heat

    Heat Well-Known Member

    The OP said they hadn’t any 10mm, but had 6mm cable for to do between pull cord & shower.
    Personally I would only use 6mm anyway for final part if shower is under 10kw.
    Much easier than 10mm to work with and some showers don’t have much space for cable.
  6. Heat

    Heat Well-Known Member

    Yes, that should be fine Carl.
  7. rogerk101

    rogerk101 Well-Known Member

    Have you looked on eBay or Gumtree for some 10mm2 T&E wire? Very often someone buys more than they needed, and they advertise the off-cut for silly money. I've picked up offcuts of heavy duty cables of >5m in the past for 99p!
  8. Sparkielev

    Sparkielev Well-Known Member

    2metrs of 10mm t&e about £5 just buy the cable and do the job properly
    Josh.91 likes this.
  9. JP.

    JP. Screwfix Select

    Concur 100% Mr S
  10. JP.

    JP. Screwfix Select

    Heat if you are running a new electric shower supply surely the standard would be to do it in 10mm minimum, and in some cases it might even require 16mm.
  11. Hollie

    Hollie Member

    Up to 10KW? If the shower was 10KW and you followed your own advice of installing a conduit then it would be non compliant.
  12. Risteard

    Risteard Well-Known Member

    Depends on the rating of the shower. There is no "standard".

    What cases exactly?
    Heat likes this.
  13. Heat

    Heat Well-Known Member

    Yes, I would do it in 10mm from consumer unit, no matter how short a distance of cable or how low a kw shower was to be installed, so to keep it suitable for a larger kw shower in the future. Only the extra cost difference in cable, so sensible
  14. Heat

    Heat Well-Known Member

    6mm cable is well within specifications for 8.5kw shower, providing it doesn’t exceed max length allowed (for 6mm doing 8.5kw) and consideration is given to cable install, such as not burying it in loft insulation.
    The cable size needed is over sized for belt and braces specification and 6mm still falls very well within that specification for most install scenarios of up to 9.5 kw showers
  15. Heat

    Heat Well-Known Member

    I was allowing for the possibility the OP had their shower on a solid wall, where that mere 900mm drop is best to be in 25mm conduit.
    Gives plenty of air around cable and will very importantly allow the cable movement in event of shower being renewed, which as we know, often results in cable being a couple inches too short.
    But the OP later said it was studding
  16. Bazza-spark

    Bazza-spark Well-Known Member

    For me, 6mm on a 40A breaker is not acceptable. You are pushing the cable rating too far. Downrate the breaker to 32A or upgrade to 10mm

    Kind regards
    Josh.91 and dobbie like this.
  17. Coloumb

    Coloumb Well-Known Member

    I would have though if it's running in 2m of insulation some form of downrating would be applicable, like it's not a lighting or power ctt.
  18. Risteard

    Risteard Well-Known Member

    Why? It only needs to provide fault protection and not overload protection. So long as the cable is suitable for the load then there is no issue.
  19. Bazza-spark

    Bazza-spark Well-Known Member

    So what in your opinion is the current rating of 6mm?
  20. Risteard

    Risteard Well-Known Member

    You completely missed the point. Overload protection is not required - a shower is a fixed load which cannot overload. Only fault protection is necessary.

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