loft insulation - 6mm shower cable

doningtonphil

Hello

We currently have 100mm loft insulation between joists in loft. I want to top it up by laying insulation across joists. The problem is that we have a 6mm cabl runningfrom the front of the house almost to the back of the house (it comes up from the consumer unit in the living room, lays loose across the joists (may be clipped in places) and then goes down to a 9kw shower).

I know the rules that the cable should not be covered by insulation but there is no way we can lift the cable to make enough room underneath - stretchy power cable, now that is something I want to see on Dragons Den - so in reality what are the risks of laying insulation over a power cable to a shower that will be used 2x 10 mins every day?

norbet

Is the cable 6mm in width or 6mm in terms of conducter area?
I'm no sparky, but 6mm sounds insufficient for a 9kw shower. I'd have thought 10mm cable is recommended.
As far as I'm aware covering it in insulation reduces the cable's ability to disepate heat, I think you maybe pushing it with 6mm cable

vaio

6mm clipped direct will carry 40+ amps

cover it in insulation and it drops to 32 amps

9 kW is about 36 amps so the advice has to be change it to 10mm.

doningtonphil

Thanks for your feedback. I am confident that as it stands the cable is adequate, my NICEIC electrician obvously thought so when he installed our bathroom electrics.

I suppose my question is a hypothetical one. What REAL effect would laying insulation over a cable have when the shower is used about 2x 5-10 min spells per day. I understand my house COULD burn down. Do cables heat up/perform differently that quckly? Is it a cumulative thing over time?

doningtonphil

Just checked. The shower is 7.5kw (mira sport). I remember desperatly wanting a 9 or 9.8kw shower and almost gettng one but then heedng the electriicans advice to go for 7.5kw due to long cable run and 6mm cable

keystone

The cable needs to be derated if its covered in insulation and operated at a lower performance spec. If it was on the edge anyway when the shower was installed then covering it sounds less than optimal.

Cheers

MX5huggy

Can you put a piece of guttering chanal over the cable giving it room to cool and the insulation. Over the top.

vaio

vaio wrote: »

6mm clipped direct will carry 40+ amps

cover it in insulation and it drops to 32 amps

9 kW is about 36 amps so the advice has to be change it to 10mm.

doningtonphil wrote: »

Just checked. The shower is 7.5kw (mira sport). I remember desperately wanting a 9 or 9.8kw shower and almost getting one but then heeding the electricians advice to go for 7.5kw due to long cable run and 6mm cable

7.5 kW is about 30 amps so the wire should be fine

norbet

vaio wrote: »

7.5 kW is about 30 amps so the wire should be fine

Yup, I'd agree - OP just be aware if you want to upgrade the shower to a more powerful one that the cable will likely need upgrading/re routing.

googler

MX5huggy wrote: »

Can you put a piece of guttering chanal over the cable giving it room to cool and the insulation. Over the top.

Or some rainwater guttering...?

Or some kind of electrical conduit...?

You can get the kind which is a U-section, with a clip-on top, which closes the U. Last time I used it, I got it from B&Q, it was about 1.5 inches wide by 0.5 - 0.75 deep - plenty of room for a shower cable to cool, I would have thought.

SmeegHeeeed

The cable is probably OK for purpose, try running the shower for 10 mins (use it don't waste water LOL), nip up there and see if the cable is hot..... if anything over normal cool, its too small.
Most of your lighting circuit will be under the existing insuklation without covers etc.

Hope you ar getting your extra 160mm of insulation for nothing.............its free until the end of October for ANYONE. (Contact availanle)

:money::money: as Martin pointed out last week on Daybreak.