Shower Switch Burning Out

Stumps · Posted: Wed May 31, 2006 6:31 am Post Subject: Shower Switch Burning Out

Hi,
I have to replace my 45A shower mains switch every year. I thought this was down to a faulty shower, so I have replaced the shower and it has also burnt out the mains switch twice. The New Shower is 9kW and it seem that it is the N pole on he input of the switch that is getting hot. Any ideas? Could it be an earthing fault? The cable I believe is 6 or 10mm - need to check, either way it should be man enough as it is only a relative short run to the consumer box.

Steve · Posted: Wed May 31, 2006 9:39 am Post Subject:

same thing happened to ours. About 5 metre run to the consumer unit, 6mm 9.5kw. Neutral completely bare and green, switch destroyed, but it still worked. We only found it because the string snapped off and had to get a new switch.

Upgraded to 10mm² cable. We put it down to a bad connection, i mean, it is understandable that such large cables in small terminals will eventually loosen, no matter how tight they are fastened to start with.

JohnD · Posted: Wed May 31, 2006 10:34 am Post Subject:

I think I heard that once a copper cable has got really hot, the copper crystallises or something, and it will tend to break down again; however tight you make it, it will come loose and give you a high resistance joint.

Metallurgy is one of the many things I know nothing about, though.

If this is right then a repair which includes a new section of cable crimped onto the cable, after cutting off the part that got hot, may be needed.

RF Lighting · Posted: Wed May 31, 2006 5:59 pm Post Subject:

I think you are right JohnD. You can see where the copper has got hot as it will be slightly duller in colour. This should be cut away and if no slack can be pulled then the cable should be joined. Make sure the connections in the switch are properly tight and there are no broken / scored strands in the cable as a high current appliance like this (as you know) is very good at finding and destroying bad connections.

Stumps · Posted: Wed May 31, 2006 8:36 pm Post Subject: Shower Switch Burning Out

Hi Guys,

Thanks for the feedback, come to think of it when I moved into my first house the mains supply tails had to be replaced, as they were smelling when loaded and the mentioned that it was better to replace them, rather than re-terminate. Sounds like the Cooper rot has set in !

I think I would be better off changing the whole cable if I can, rather than fitting a JB.
All connections are nice and tight at all terminating points and I have bought good quality DP switches, so running out of ideas.

cheers

savage · Posted: Thu Aug 10, 2006 3:38 pm Post Subject: Burn out

I have had a similar problem, in fact worse i am replacing swiths at a rate of two a year! I have started to wonder if it is actually the position of the switch/pull cord itself, I think mine is getting full of steam and this is creating the shorting and melting in the switch. I am going to move my switch outside the bathroom and see if this works. I could be completly wrong but it is a preferable option to running new cable, espescially 10mm cable

Steve · Posted: Thu Aug 10, 2006 6:58 pm Post Subject: Re: Burn out

savage wrote:

I have had a similar problem, in fact worse i am replacing swiths at a rate of two a year! I have started to wonder if it is actually the position of the switch/pull cord itself, I think mine is getting full of steam and this is creating the shorting and melting in the switch. I am going to move my switch outside the bathroom and see if this works. I could be completly wrong but it is a preferable option to running new cable, espescially 10mm cable

what size cable do you currently have? what is the rating of the shower? and how long is the cable to the shower in total, from the fuse box/consumer unit?

RMS · Posted: Thu Aug 10, 2006 7:11 pm Post Subject:

crafty1289 wrote:

same thing happened to ours. About 5 metre run to the consumer unit, 6mm 9.5kw. Neutral completely bare and green, switch destroyed, but it still worked. We only found it because the string snapped off and had to get a new switch.

Upgraded to 10mm² cable. We put it down to a bad connection, i mean, it is understandable that such large cables in small terminals will eventually loosen, no matter how tight they are fastened to start with.

Is it just me or is it always the neutral conductors that overheat/melt first as a pose to the live. Well, most of then time anyway?

RF Lighting · Posted: Thu Aug 10, 2006 7:28 pm Post Subject:

RMS wrote:

Is it just me or is it always the neutral conductors that overheat/melt first as a pose to the live. Well, most of then time anyway?

I seem to remember the IEE did a study into this, and found the neutral does burn out more commonly than the live. They said it was a subconcious thing, thinking that the neutral is less important that the live, resulting in folk not always paying as much attention to 'nipping up' the neutral as the live.

securespark · Posted: Thu Aug 10, 2006 8:36 pm Post Subject:

Deja Vu???

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Adam_151 · Posted: Thu Aug 10, 2006 10:30 pm Post Subject:

RF, think your memory may be fuzzy...

I remember saying that the topic had come up on the IEE forum and the conclusion of the thread was that it was a subconcious thing before going onto wild theories about fields etc, it wasn't like an official IEE thing or anything, just a group of electricians, electronics designers, etc on a forum all trying to come up with a reason

RobbieRocketPants · Posted: Wed Feb 11, 2009 11:45 am Post Subject:

I have the same problem - 2 burnt out 50Amp pull-switches in 1 year. I have a 10.8KW shower which should draw less than 50Amps. (10mm cable). I have tried a Volex switch and an MK switch.

Does anyone know if you can get any better switches or even a 60Amp pull-switch ?

Cheers,
RRP

ban-all-sheds · Posted: Wed Feb 11, 2009 12:04 pm Post Subject:

But anyway - I've got a 10.5kW shower on an MK switch, and it's been absolutely fine for several years.

It's not the fault of your shower, or of your switches - your problems are entirely down to the switches not being properly installed...

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Steve · Posted: Wed Feb 11, 2009 1:22 pm Post Subject:

No ban, its down to the switches being ridiculously hard to install, due to their small size and terminating huge cores into them.

I'm gonna use a contactor and a 10A switch when it comes to replacing my shower switch next.

IMO its safer than using a shower switch.

ban-all-sheds · Posted: Wed Feb 11, 2009 2:09 pm Post Subject:

ban-all-sheds wrote:

I've got a 10.5kW shower on an MK switch, and it's been absolutely fine for several years.

__________________
I mustn't warn people that the "experts" on the plumbing forum can't be trusted to tell the truth.