New shower circuit

[Rob69]

I have a new circuit shower to fit with no old circuit to use.I am correct in saying i cannot run cable in the cavity ( regs )to reach the loft for the drop down into shower.

Is it ok to chase up internal walls to achieve this with metal capping of course?

Cheers Rob

 

[NozSpark]

So long as you use the safe zones then that's acceptable....and RCD protection of course

 

[Manator]

One of the problems amongst others when running a cable in the cavity is the length of cable left without any support, now, we all know we have a minimum spacing regulation for cable support.

 

[SteveT]

BRB not to hand but you can run vertically down a cavity for I think 5M unsupported, but need to check BRB

 

[Evans Electric]

If " unsupported " is the only criteria how about tywrapping cable to a support wire and dropping it down the cavity.

Tell you what........it would be down the cavity for me!!!

 

[chrishaworth]

The IET forum's opinion is that cavities should not be used for cables because: 1) cable could bridge across creating a path for damp, 2) cavity insulation could be blown in severely derating the cable and 3) you have no idea what sh*t is in the cavity which could damage your cable. Number 2 in this day and age is increasingly likely and with a 9Kw shower, it would need 16mm cable to run the 39A required. Don't do it.

Cheers, Chris

 

[Rob69]

Thanks all , confirmed what i thought,cheers

 

[Evans Electric]

Anyone ever heard of a cable conducting damp across a cavity ?

Also when you say cavity wall I imagine an empty cavity with no lagging or the injected stuff in there.

I'd question the 16mm for the 9KW shower TBH ,Chrishaworth, I've seen small factories being run on a 16mm . I'm not picking flys but I wonder where some of the guys get their choice of cable size from.

 

[chrishaworth]

16mm is the size required to run 39A using RM 103 - BRB pg 282.

Cheers. Chris

 

[m4tty]

I've seen 4 bedroom houses on 10 mm tails before lol

 

[Pits]

I would also install a 30ma RCBO as well as mechanical protection (metal capping)

 

[Zeespark]

Metal capping isn't suitable as mechanical protection Pits, it has to be a minimum of 3mm thickness I believe, which capping isn't.

AndyGuinness

 

[PC Electrics]

I usually run swa up the outside into the loft in this situation. You're unlikely to have safe zones through the upstairs rooms to go inside.

Shouldn't use the cavity - in this day and age it is highly likely to get filled with insulation soon and may bridge the leaves and allow water flow (i think other build regs have summat to say about this).

 

[Riggy]

You're unlikely to have safe zones through the upstairs rooms to go inside.

What about the safe zone in the corner of every room?

 

[stephen36]

i used a bit of trunking to take me up to the ceiling and came out in the airing cupboard and str8 up into the loft, used trunking in the cupboard as well. the metal capping you dont really need your cable is protected by rcd and lets face it if some1 drilled into wall they would go str8 through capping as its rubbish really of if hammering a nail dont know why they sell it for lol.

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i agree 10mm is adequate for a 9kw shower and 16mm is unessacery and a pain in the bum to terminante into your double pole switch lol.

 

[Evans Electric]

I still question using 16mm for a shower , unless its 3 miles away, perhaps its time I packed up.

 

[Zeespark]

Providing you can keep the 10mm away from insulation for showers, the 16mm wont ever really be needed.

AndyGuinness

 

[PC Electrics]

I still question using 16mm for a shower , unless its 3 miles away, perhaps its time I packed up.

I don't understand this predeliction with putting showers on massive cable. In accordance with BS7671 a 10.5kW shower pulls 43A, so provided you can keep the cable clipped direct (or buried in plaster) and can fit a 45A fuse/mcb then it can go on 6mm (ccc for 6mm in this instance is 47A). Yet everyone seems to scream from the rooftops that you must put any shower over 9kW on 10mm !!! Very unlikley to have vd problems in most houses.

I avoid insulation by putting verticle sections of cable through 4 inch soil pipe to maintain an air gap around the cable and clipping to woodwork well above the insualtion layer for the rest of the run.

 

[Evans Electric]

Ah !! The voice of reason from Mr PC . That is the very essence of it, the length of run in most houses is not great .

The other criteria (to me anyway) is that a shower works for ,say, 10mins , the cable starts thinking about warming up and its switched off.

I didn't like to say it but 16mm is so OTT .

 

[PC Electrics]

Thanks Ev. You hit one of the other nails squarely on the head - shower operation is almost never continuous. Continuous is generally defined as operating for 1hr or more. In the example given, I'd have no compunction putting it on a 40A mcb if a 45 was not available for the particular make of board. A 40 will [almost] never trip with a continuous 43A load!! Even this will still meet the reg about avoiding small, continuous overload, by simple dint that the load is not continuous!!!

What really gets me about this subject though is that people don't seem to be able to follow the ccc tables of 7671. Why do they feel the need to "play it safe" - BS7671 already has the safety factors engineered in.

It's a bit like buying a 200HP car and putting a block under the throttle so you can't use more than half power in case you 'strain' the car too much!!