Advice on extending shower cable

Discussion in 'Electricians' Talk' started by Tom Bartonn, Feb 12, 2024.

  1. Tom Bartonn

    Tom Bartonn New Member


    I recently moved my electric shower unit to another wall during a bathroom renovation. I initially extended the cable with 6mm T+E cable, connected with a 32A push-fit connector.

    I want to improve the quality here, as we will need an electrical certificate.

    I'm planning on crimping the connection with 6mm butt joints, and putting that in a waterproof box within the wall behind the shower. This was on recommendation from our electrician doing the certification. I had a couple of specific questions on this, to make sure I do a decent job:

    - What IP rating would be best? I see a few boxes with IP55.
    - Would you use cable glands on the sides for the two wires entering the box, or is this more for outdoor applications? I could silicon the holes instead.
    - It might be a silly question, but some boxes I see don't have screw holes that are separated from the waterproof compartment. I would be compromising the waterproofing if I screw through it, so how would you affix the box to the wall?

    Would appreciate any opinions on this. This won't be my last bathroom renovation, so I want to make sure I learn all I can this time.
  2. The Happy Builder

    The Happy Builder Screwfix Select

    Awful job, which is not about to be made any better.

    If you need an electrical certificate employ an electrician to do it properly.

    Is there any reason why the cable cannot be simply replaced from the isolation switch to the shower instead of the existing being extended?
  3. The Happy Builder

    The Happy Builder Screwfix Select

    I would tell him to ride off into the sunset.
  4. WH55

    WH55 Screwfix Select

    Was just about to say exactly the same. Surely you can replace the cable from the shower to the isolator switch / pull cord ? Or is that not accessible or nearby ?
  5. Tom Bartonn

    Tom Bartonn New Member

    So there was no isolator switch at the shower in the first place. Replacing the cable would mean running it back to the fuse box, unless it makes more sense to add an isolator switch outside the bathroom
  6. WH55

    WH55 Screwfix Select

    In that case, pull back the existing 6mm cable to outside the bathroom and into an isolation switch (better with a switch than a pull cord in the bathroom, in my opinion).

    As you pull back the existing cable, pull a draw wire through to allow you to add a new length of 6mm from the isolator to the shower. No joins and a lot less faffing around to achieve. As a general rule, avoid joining cables as much as possible, particularly in inaccessible locations, as it’s a pain in the a@@ when they fail.
  7. Tom Bartonn

    Tom Bartonn New Member

    Okay, thanks for this. Switch outside the door is most practical anyway as the bathroom is very small and would be hard to position a switch. I'll get an isolator sorted rather than the join (and will make sure not to join the cable in the future!)
  8. DIYDave.

    DIYDave. Screwfix Select

    All sounds weird to me really -

    Unusual that the electrician issuing the certificate is totally happy for you to extend the cables and make connections inside the wall and then what, he’s gonna test and issue the certificate ? This is a common theme on the forum where the householder / diy’er plans to run cables / fit accessories / etc and just get the friendly sparky to pop in, test and sign off - isn’t usually recommended way to go

    Will the cable joint be accessible for inspection once inside the wall ?

    And even if a joint is acceptable, why would you need an IP rated box within the wall ?

    Maintenance free for sure but IP rated - as recommended by the spark ?
  9. Tom Bartonn

    Tom Bartonn New Member

    Yep, the electrician said it doesn't need to be accessible, but I said if a join (which I'll isolate it now anyway), then I could leave it open for him to check it. I would have then plastered the wall, so it wouldn't be accessible. In terms of IP rating, yea it shouldn't be at all necessary, as the shower is completely waterproofed, but the shower is on that wall, so I think it was an added precaution.

    Following WH55's comment though, it makes a lot more sense to install an isolator and run a new cable from that to the shower. Sounds safer anyway than the initial setup that had no isolator. Then it will be accessible and have no join.
  10. WH55

    WH55 Screwfix Select

    Make life easier for yourself by getting a slightly deeper back box than is recommended and also also paying a bit more £ to get a decent make of switch. Secondly, once you tighten the terminals on the switch plate, dress the cables into the back box and then leave it for a while. Go back and re-check the terminations once they’ve settled for a while. They can loosen off and it’s dangerous.
    arrow likes this.
  11. Tom Bartonn

    Tom Bartonn New Member

    Nice one, that's good to know. Thanks
  12. The Happy Builder

    The Happy Builder Screwfix Select

    What is the kilowatt rating of the shower?
  13. Tom Bartonn

    Tom Bartonn New Member

    7.5kW Triton Cara
  14. WH55

    WH55 Screwfix Select

    Did you say earlier that it’s on a 32amp MCB / RCBO ?
  15. arrow

    arrow Screwfix Select

    I would run a 10mm cable from the new switch position to the shower. If in the future you put in a bigger shower you will only need to rewire to the switch.
    WH55 likes this.
  16. Tom Bartonn

    Tom Bartonn New Member

    I would have to check this, though I think it is rated higher than 32 amp - I just matched the same cable as came out of the fuse box. I do know the fuse box is RCD protected.
  17. Tom Bartonn

    Tom Bartonn New Member

    If a 6mm cable runs from the fuse box to the isolator, and I have a 10mm cable from the isolator to the shower, that is fine?
  18. Wellwisher

    Wellwisher Well-Known Member

    Having an isolator does not make it safer. It adds an additional point of possible failure, and believe me they do fail. Most likely because people insist of isolating after every use. Their only use is isolating for maintenance and on the rare occasion that is required you can isolate at the CU.
  19. WH55

    WH55 Screwfix Select

    Yes, that’s fine. Arrow makes a good point.
    Tom Bartonn likes this.
  20. WH55

    WH55 Screwfix Select

    Better than a joint inside the wall.
    Ind spark, Tom Bartonn and Coloumb like this.

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