Shower ceiling switch shorting out?

[kma2k]

Hi, wondered if anyone could offer an explanation of why this happens?
The ceiling mounted switch for our 9kw shower began to get stiffer - not switching off cleanly and yesterday I heard what I assumed to be some 'arcing' in the switch. It was hot to the touch and beginning to smell a bit, so I swapped the switch for a new one.

The neutral wire on the feed side had clearly been getting hot - it was held securely by the screw but the insulation had charred and the copper strands were blackened. I cut this back before re fitting.

Is the load too much for the wire? We're just starting to use the hotter settings on teh shower - using both of the elements. Why does it just happen at the switch? is it just a by product of the ceiling switch failing? It has happened before, but probably 2 or 3 years ago without any re occurrence.

Help? View media item 85653

 

[EFLImpudence]

Loose terminal or poor switch contact.

 

[Jackrae]

Or cheap switch. A good price doesn't always mean a good product

 

[kma2k]

Thanks guys,
I've gone with MK usually, admittedly bought from a DIY Shed, but they're usually a good product I think. The replacement was MK again, so I'll keep an eye on it - check the tightness of the terminal again for good measure. Its the correct wire although it is at its limit at 9.0 kw i think - didn't want to go any higher for fear of overloading, but the responses put my mind at rest. There's another in the house which hasn't been nearly as troublesome.

 

[Steve]

The switch failed because the terminal worked loose and heated up the innards under load.

IMO These switches are a very poor design, always have been. To get two 10mm cables into the enclosure is bad enough, but to then work four cores into the live terminals, and two earths into the final terminal, and squash it all up into the ceiling or backbox - takes skill and a certain degree of brute force usually.

By the way, the neutral failed because of a psychological aversion to tightening it up as much as the live.

You must cut back to fresh copper before you reterminate the cable.

I opted for a mixer shower running from the combi boiler rather than have one of these stupid switches in my house (and its just better at giving a good shower! My boiler is 28kw!)

 

[ban-all-sheds]

To get two 10mm cables into the enclosure is bad enough, but to then work four cores into the live terminals, and two earths into the final terminal, and squash it all up into the ceiling or backbox - takes skill and a certain degree of brute force usually.

Or it takes a rear entry into the box and two short pieces of flexible conduit. Assuming there's a floor void, why not use it?

 

[kma2k]

Thanks both , I'll check the terminal periodically to see if it is working loose - couldn't have been tighter this time - needs to be to get all of the wires back into the box - its in the loft rafters above the ceiling so there's some slack left to push back through.
All the embritteled insulation was cut back and shiney copper exposed - the head would have been considerable. Its on the list of things to watch more regularly now.

 

[Adam_151]

To get two 10mm cables into the enclosure is bad enough, but to then work four cores into the live terminals, and two earths into the final terminal, and squash it all up into the ceiling or backbox - takes skill and a certain degree of brute force usually.

Or it takes a rear entry into the box and two short pieces of flexible conduit. Assuming there's a floor void, why not use it?

Rear entry, yes...
Short lengths of kopex... no!

If you have used the correct 47mm deep box and are able to push cable into a void space behind then you can make it off and keep all the unsheathed cores inside the box as per traditional practice, rather than ****ing around containing them in kopex!