9kW shower wiring.

[alcazar]

Hi all, first post, so please bear with me.

Some years ago I fitted an electric shower in my youngest son's bedroom. It has a ceiling pull switch outside the shower.

Shower is 9kW.

It was wired with 6 sq mm cable. It has always (about every year or so) needed new ceiling switches, despite me using hager products rated at 50A+

Last time, the live feed to the switch was partially melted and the cable had to be cut to remove the switch. Checking further back and the cable is undamaged except for the last 25mm or so.

I am reliably informed that I need to go up to 10 sq mm cable. Pulling it through would be a nightmare, and I don't really want it in a conduit outside.

However....when I fitted the shower above, I also ran a second length of 6 sq mm cable, which was to power a second shower that never got fitted. It's still up there.

Is there any reason why I cannot now parallel the two cables? Both will fit into the feed mcb (50A) and at the shower end, couple to a shorter length of 10 sq mm using a DP Henley Block, then run 10 sq mm to the switch, and from switch to shower?

Thanks for any advice.

 

[Andy™]

cables can be doubled up, however some conditions have to be met, i.e both same CSA (different is possible but gets more complicated) and same route etc. what you propose doesnt sound too bad, however henley blocks are designed for DI tails, not T&E, so you'd need to put it into an enclosure otherwise youd have cables with only single insulation at the connections

 

[Ardet R]

Welcome to the forum.

The parallel arrangement has been covered by Andy.

However it is not very likely that the size of the cable is the issue, if this were the case then the damage would occur at other points in the circuit as well.  It is more likely that the cable termination in the switch terminals is failing and causing the local overheating.  Ensuring the cable being connected is clean bright copper and not suffering from heat corrosion and also ensuring the cable is firmly held in the terminals even after is has been manoeuvred back into position and the screws remain tight should prevent this sort of problem.  Terminating two cables into the switch terminals will require even greater care to ensure they are securely terminated.

 

[Andy™]

yes, is always that. decent. decent switch and you should be OK. fit  crabtree pull switch, best one imo and rarely fails with dodgy conenctions

 

[Phoenix]

There shouldn't be an issue with the hager pull switches IMHO, what I think there is a problem with (and I mean no dispespect to the OP y this) is switches fitted by DIYers.

Its important to take time dressing the cables in, otherwise if its just forced back, things move and work loose. My own personal approach (some might chime in with variations, but theres many ways to skin a cat..!)

If you have any overheated (discoloured copper) you must cut it it back, Orient the cables comming through the ceiling so that the conductors match where the terminals will be on the switch, you dont want to have to cross them over, bind the cables together with tape to keep them like that. Strip the grey sheath of, but a leave about 6 inches on which will get pushed into the ceiling to leave you some spare and allow you to work. Put a set on each conductor, such that it flows neatly to its terminal, and then straightens out straight. (also be midful that this needs to fit in the back box and the blue and brown must not stick out the back into the loft!) Cut and strip the conductors to the right length to have the proper amount of copper in the terminal and none showing. Put the switch on all conductors and tighten the terminals. Next sleeve the earths and dress them so they run through the middle of the other conductors towards the middle of the switch then turn and flow nicely into the earth terminal, ith 2.5mm  solid cores, double them over. Now go and retighten all the terminals, push the switch up and guide the slack into the void above and test fit it to the back box, very little presure should  be needed to get it into the back, pull it back down slighly and give tightness one last check before screwing it back.

(Easier with pictures I know, but I have't got any)

I've never had to change a switch that I've fitted, but I've changed many that others have fitted and generally they look like they have just been rammed home

Andy, Crabtree switch is nicely designed from point of view of installer, but looks a little ugly and out of place IMHO

 

[Andy™]

Andy, Crabtree switch is nicely designed from point of view of installer, but looks a little ugly and out of place IMHO

there not the best looking, but good connections that you dont need to disturb whilst putting cover on / removing

 

[Evans Electric]

there not the best looking, but good connections that you dont need to disturb whilst putting cover on / removing

Best switch available to handle 6.00mm & 10.00mm  . 

And its designed to span a ceiling joist  so you get your two fixing holes  lined up on timber  ...and  the  terminal pairs are  each side of the joist  , top quality , top design  ( and not much of that these days )  Never known one burn out . 

 

[Murdoch]

Andy, Crabtree switch is nicely designed from point of view of installer, but looks a little ugly and out of place IMHO

Ugly - no

Out of place - why

Reliable - 100% based on my expereince

 

[alcazar]

Thanks for the responses.

Having done almost all the wiring in a new part of a house we were trying to renovate in France, (yeah, I know: different regs), I know all about tighten, then retighten screws and make sure cable runs are sensible to switches, junction boxes etc. So I'm pretty sure it's not that.

I might look into a henley box for the solution, but, as said, place it in an enclosure. Any ideas for an enclosure?

 

[binky]

how many kW is the shower?

 

[Andy™]

how many kW is the shower?

9

maybe a trip to specsavers?

 

[binky]

missed that bit  :shakehead .

 

[alcazar]

Yeah, it's a 9kW. Not done anything yet, it's just got bare wires hanging out of the ceiling, but the room is spare and it's isolated at the consumer unit.

Wife's long term in hospital, so not a deal of time left for stuff....