Still need help on shower cable

Discussion in 'Electricians' Talk' started by Guy, Jan 23, 2004.

  1. Guy

    Guy Member

    Some days ago, I posted on this forum query about shower cable size.

    Well, now perhaps I should explain things more clearly.

    I let (rent it out) a studio flat that needs a new shower.
    I have taken out the old shower which was a 7.2KW.
    I am thinking of replacing it with an 8.5KW as Screwfix don't seem to do a 7.2KW showers anymore.
    The cable run is about 4 metres (5 at most).
    Will this cable that fed the 7.2KW shower be okay for a new 8.5KW? I am not sure what size the cable is, but I know it suited the 7.2KW shower fine.
    I really don't want to go to the trouble of putting in a new cable, and considering that this run is so short, I'm hoping that you electricians will agree that it will be quite safe.

    Thanks for any help offered.
     
  2. gerrin2owd

    gerrin2owd New Member

    If you dont know what size the cable is, you dont know that it was fine for 7.2kw (just because shower works does not mean everything must be ok). It depends on whether its clipped direct to the surface or enclosed in plaster or conduit, singles or Twin & Earth.

    With such a short run why not install a 10mm2 cable on a 40 amp mcb? Not cost much - and peace of mind :) now that is worth having!
     
  3. Guy

    Guy Member

    Thanks for your reply.
    The cable is quite heavy stuff, and was fitted when the flats were built about 20 years ago. So it should be the correct cable for at least 7.2KW.
    This is the reason that I said "the 7.2KW shower seems fine".
    Okay, assuming that the cable IS suitable for 7.2KW shower, as the run is only about 4 to 5 metres, will the cable be adequate for an 8.5KW shower?

    Thanks.
     
  4. gerrin2owd

    gerrin2owd New Member

    Worst case scenario if the cable is 6mm2, it would be overloaded by 5A. You decide if it is adequate,I reckon not!
     
  5. Guy

    Guy Member

    gerrin2owd,

    I have just been looking at a Readers Digest book, and in it I have found info on cables for showers etc.
    It states that 6mm2 Twin & Earth can serve cookers upto 13KW and also for shower circuits for 13metres to 20metres cable run. So surely your post (above) is wrong isn't it?
    My run is only about 5 metres and I only want an 8.5KW shower. So 6mm2 should be fine.
    Surely this is okay?
    Perhaps someone else can give their opinion on this.

    Thanks.
     
  6. Thevitalspark

    Thevitalspark New Member

    g20 is correct, although I think the worst case scenario for the existing 20yr old cable could be 4mm, 30A.

    It's a short run, upgrade the cable to 10mm,install a 30mA rcd,40A mcb and check your existing shower switch (if fitted) is rated at 45A.

    G
     
  7. sparkydude

    sparkydude Member

    Providing the cable is a 6mmm cable and the run is as you say 5 metres at most it will be fine, but will need to be on an rcd and must run through a double pole isolator to comply with the regs, 10mm is for big showers 9.5kw and above i would say as its a ***** to get into the terminals of a switch

    Nick
     
  8. Sheriff_of_Cosham

    Sheriff_of_Cosham New Member

    I've got a similar problem, and I can sympathise with Guy - routing 10mm cable is not something I look forward to doing. I've got a 6kw shower currently installed and want to change it for a bigger one. So I bought a 10.5kw as I mistakenly thought the supply cable was already 10mm. It now turns out it is only 6mm (cable is not enclosed in conduit and run length is about 12m).

    According to the fitting instructions, upto 28m run length, 6mm is rated at 46A and 10mm rated at 63A (when clipped direct or not buried in an insulated wall). As the 10kw shower draws 43.8A at 240v, one could conclude that 6mm is OK.

    Do any of you professionals have an opinion on this? I'd be interested to know before I return the shower and get a lower powered one. BTW. Is there a world of difference between 10.5kw and say 8.5kw in outright performance?

    Thanks
    Spence.
     
  9. gerrin2owd

    gerrin2owd New Member

    A cooker circuit allows for diversity, i.e. all elements not switched on at once, a shower circuit doesn't allow for diversity.

    If your shower cable is clipped on the surface, it would comply but I suspect that it is buried in plaster. My answer is based on table 4D2A page 222 of the regs.

    To be compliant with the IEE regs I stand by what I said previously.
     
  10. sparky Si-Fi

    sparky Si-Fi Screwfix Select

    I would run 10mm for any shower above 7.5 kw (if they still are available)6mm would do the job,but if I was designing the job,10 mill would be prescribed without question.

    Sorry to be a blunt as I know how a pain 10 mm can be to run/terminate,I to stand with G20,any money your cable is buried in plaster.

    Run 10mm for peace of mind,who knows you may want to up-grade to a 10.5 Kw later on.
     
  11. rayall

    rayall New Member

    Guy,

    If your certain this cable is a 6mm then it should cope with a 8.5Kw shower without any trouble. The max current drawn from your shower would be 36amps where a 6mm T&E will as a rule of thumb will cope with 45amps.

    If your still not happy check out <u>www.aeicables.co.uk</u>

    The cable sizing wizard may help you to put your mind at rest.
     
  12. gerrin2owd

    gerrin2owd New Member

    Guy,

    If your certain this cable is a 6mm then it should
    cope with a 8.5Kw shower without any trouble. The max
    current drawn from your shower would be 36amps where
    a 6mm T&E will as a rule of thumb will cope with
    45amps.

    If your still not happy check out
    <u>www.aeicables.co.uk</u>

    The cable sizing wizard may help you to put your mind
    at rest.


    OK have a look at the IEE table 4D2A for yourself, here it is:-
    http://www.batt.co.uk/catalogs/industrial/tech1.htm
     

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