Shower electrics melting

[andrew299]

Hello all,
I have a strange problem.
The shower in my bathroom was installed 18months ago. It is a 10.5kw shower and I think a 10mm2 cable.
It worked fine for a year until one day the pull cord stopped working.
I opened it up and found that some white plastic had melted over the cord stopping it moving. I assume that this is some sort of safety feature if the cable gets too hot?
Any way, the live cable was black and the insulation melted. I replaced the pull switch with a new one and stripped back the cable and insulation so that it was clean. After about a month the same thing happened. I thought perhaps the terminals had come loose when I fitted it and also I had used a cheaper make switch. So I replaced it with an MK one making sure that all connections were tight and that the cables fitted into the back of the box tidily.
This again lasted a couple of months.
What is happening? surely if the cpacity of the shower (10.5kw) was too much for the cable this wouldn't have taken a year to manifest itself in the first place.
Can anyone suggest what else could be the problem.
Thanks

 

[Chri5]

10mm cable should be ok, but......

What sort of distance is there between the shower and the main board, can you follow the route and explain how it runs ?

i.e. from switch to loft void, 3m in loft insulation, down airing cuboard (clipped / surface) etc

 

[andrew299]

thanks for the reply,

the shower is downstairs. The routing of the cable is approx 5ft shower - pull switch
then
pull switch - fuse box approx 20-25ft running between ceiling and wooden floor above so I don't think any insulation. I cant pull any more of it through so I assume that it is clipped in places but no way of telling

 

[pjcomp]

... the live cable was black and the insulation melted....

This usually means the terminals haven't bene tightened up enough, leading to arcing across the terminal which damages rthe insulations and overheats the switch. Are you being completely ruthless when you tighten those screws! Are you certain the cable is 10mm? Is there an RCD fitted?

PJ

 

[electronicsuk]

You also need to strip back the cable a fair way past the heat damage. Remember, copper is a pretty good conductor of heat, so the damage wont be restricted to just the small portion of cable that goes in the terminals.

 

[RMS]

Is the shower in use for long periods of time?

As said, make sure you get your terminals really tight and make sure your screwdriver is the correct size for the screw.

 

[andrew299]

Thanks for the replies,
I will strip the cables back a good distance from the damaged areas and refit a new pull cord (probably MK) and make sure the terminals are tight.
Would it be worth crimping a little nodule ( not sure what they are called) onto the end to ensure a good connection?

 

[electronicsuk]

A ferrule might help, but they are not likely to be locally available for 10mmsq conductors, nor are the crimp tools for them particularly cheap. I've never seen anyone bother with this before, not have I, and the isolator switches on my showers all seem just fine.

 

[flameport]

refit a new pull cord (probably MK)

The MK one is no better than most of the others.

The Crabtree one is vastly superior.
http://www.screwfix.com/prods/90597/

Crimping anything on the end isn't necessary and won't help at all.