Strange cooker switch incident

Interslice

One of my housemates noticed the cooker switch was roasting hot today. Oven was on full whack and two hobs going. The power light on the hob started to flicker. So I pulled off the switch just now and the two neutrals were loose and mildly burnt. One of the lugs that should have been holding one of the neutrals in fell onto the counter as I was removing the switch.

So which came first the chicken or the egg? Any one come across this before. Was this a case of a dodgy sparky or tiler maybe leaving them undone. Surely the lug wouldn't fully unscrew itself . All other connection were sound just the two neutrals left completely open.

Outkast_IRE

Interslice wrote: »

One of my housemates noticed the cooker switch was roasting hot today. Oven was on full whack and two hobs going. The power light on the hob started to flicker. So I pulled off the switch just now and the two neutrals were loose and mildly burnt. One of the lugs that should have been holding one of the neutrals in fell onto the counter as I was removing the switch.

So which came first the chicken or the egg? Any one come across this before. Was this a case of a dodgy sparky or tiler maybe leaving them undone. Surely the lug wouldn't fully unscrew itself . All other connection were sound just the two neutrals left completely open.

I came across this once before, but the root cause that time was incorrect wiring of the switch.

Interslice

Outkast_IRE wrote: »

I came across this once before, but the root cause that time was incorrect wiring of the switch.

Melted switch you mean?

Bruthal

Terminals loose by the sound of it.

Outkast_IRE

The reason it was discovered was the switch itself stopped working properly, and when removed it was clear to see it was wired incorrectly, and the switch had begun to melt at the plastic at the rear and the cables to it were after heating up.

In your case it could be faulty wiring / terminals loose.

Bruthal

Outkast_IRE wrote: »

The reason it was discovered was the switch itself stopped working properly, and when removed it was clear to see it was wired incorrectly, and the switch had begun to melt at the plastic at the rear and the cables to it were after heating up

Yes loose connection tend to overheat, oxidise, and then stop conducting properly, and start arcing sometimes. Once overheating starts anyway, the switches don't last long.

Interslice

Bruthal wrote: »

Yes loose connection tend to overheat, oxidise, and then stop conducting properly, and start arcing sometimes. Once overheating starts anyway, the switches don't last long.

All of this, caught it before the arcing I think.

Cheers lads. Thought this was the reason just a bit baffled that someone would do this. I shouldn't be too surprised though really some of the crap you see.

Outkast_IRE

Interslice wrote: »

All of this, caught it before the arcing I think.

Cheers lads. Thought this was the reason just a bit baffled that someone would do this. I shouldn't be too surprised though really some of the crap you see.

You would be surprised at the amount of DIYers that make a balls of simple things like a switch, or even double checking terminal connections are right.

tomdempsey200

Outkast_IRE wrote: »

The reason it was discovered was the switch itself stopped working properly, and when removed it was clear to see it was wired incorrectly, and the switch had begun to melt at the plastic at the rear and the cables to it were after heating up.

In your case it could be faulty wiring / terminals loose.

faulty wiring?

Outkast_IRE

tomdempsey200 wrote: »

faulty wiring?

Wrong term I suppose, but basically the live neutral, on both the load and supply side were wired to incorrect terminals in the switch and the switch terminals weren't tight enough

tomdempsey200

loose wires,cheap switches
can't think of any incorrect wiring scenario that might cause it

Bruthal

Yea loose terminals and/or cheap switches are the causes.

Terminals do loosen slightly after first terminating. So they need to be good and tight at the start, without overdoing it.

Quite a few seem to barely tighten them.

Bruthal

Outkast_IRE wrote: »

You would be surprised at the amount of DIYers that make a balls of simple things like a switch, or even double checking terminal connections are right.

Yea it looks simple, but the diy'r rarely if ever does it right.

maxfresh

seen this a few times loose connection is the problem will eventually burn out the switch and damage the wiring because of the arcing

Bruthal

Arc detecting breakers next maybe. Detect random brief current interruptions or transients, and trip.

Danny Mulcahy

Seen it more often then I should.
In theory a loose connection is a ticking time bomb

tomdempsey200

i tighten all connections well

i don't recall being called called back to a burnt shower or cooker switch i fitted myself

although i've seen lots of them

Interslice

The worst i seen was a neighbours switch that had about a foot of cable mashed into the box and alot of exposed wires at the terminals. They said it had never been touched since the house was bought new. It was really badly melted. Must be decent flame retardant in the switch and wires for it not to have gone up.

Bruthal

tomdempsey200 wrote: »

i tighten all connections well

i don't recall being called called back to a burnt shower or cooker switch i fitted myself

although i've seen lots of them

Yea I think its a case of connections being barely tightened in most cases. Connections loosen slightly, after they are first made, so they need to be properly tightened at the start.

tomdempsey200

ya,i wondered is ..

shallow boxes,switching on-load and cheap switches a major factor in this at all?

Bruthal

tomdempsey200 wrote: »

ya,i wondered is ..

shallow boxes,switching on-load and cheap switches a major factor in this at all?

With cooker and shower switches, id say they are probably never really switched on load. Like yourself, I cant remember ever replacing a burnt one I did myself.

Maybe they just wouldnt call me back:D

Danny Mulcahy

A shallow box would cause movement when first screwing the switch to the wall so may start the loosening process but as said above rule number one is make sure it is fully tightened from the start.

A common issue with any socket and switch is when the outlet itself loosens and people don't tighten them back up.
Every time a plug or switch is switched you will be moving the cables behind.
This will cause the connections to loosen over time or just possibly snap

Bruthal

Danny Mulcahy wrote: »

Every time a plug or switch is switched you will be moving the cables behind.
This will cause the connections to loosen over time or just possibly snap

I was going to post a bit on that in last post there, and thought someone else might. It possibly does happen alright, but id say its minimal if connections are made properly in the first place.

Leave shower and cooker isolators on, and they will last longer.

Danny Mulcahy

Bruthal wrote: »

but id say its minimal if connections are made properly in the first place.

Yes that's it..Follow rule number one and all should be good for years

Danny Mulcahy

Bruthal wrote: »

Leave shower and cooker isolators on, and they will last longer.

I personally always isolate the shower after use.
I used to leave to cook switch on till the little ones realized there was a lovely line on nice knobs to turn on the cooker!!!!:rolleyes:

Bruthal

Danny Mulcahy wrote: »

I personally always isolate the shower after use.

Many seem to. I leave the isolator on myself though.

brightspark

Danny Mulcahy wrote: »

I personally always isolate the shower after use.
I used to leave to cook switch on till the little ones realized there was a lovely line on nice knobs to turn on the cooker!!!!:rolleyes:

In your case it is better to switch off the cooker, can't see any real reason to turn off the shower though.

Off Topic.. I was in a factory several years ago that had a disused kitchen with an electric hob. One of the rings had been left turned on, but with the main switch off. A cardboard box was subsequently left on top of the cooker hob as the room was just being used for storage.

All ok until another box was pushed onto the counter top, of just the right proportions, turning on the switch. A short while later the smoke alarms were triggered!

It took at least three full fire extinguishers to put the fire out!

Danny Mulcahy

brightspark wrote: »

can't see any real reason to turn off the shower though.

Yes no harm in leaving it on once the pipe work is bonded and the shower is RCD protected.

more habit now more than anything else!!

Sounds like a close shave in the work place.
It could have got nasty.

danjo-xx

Danny Mulcahy wrote: »

Seen it more often then I should.
In theory a loose connection is a ticking time bomb

Can over tightening a screw cause any danger electrical wise (apart from the obvious ringing of the thread etc) could it cause burning or welding of the screw into the copper and what are the effects of that.

Danny Mulcahy

danjo-xx wrote: »

Can over tightening a screw cause any danger electrical wise (apart from the obvious ringing of the thread etc) could it cause burning or welding of the screw into the copper and what are the effects of that.

If the thread is wrung it will not tighten fully so is a loose connection.
Worth replacing to be on the save side.

Bruthal

Danny Mulcahy wrote: »

Yes no harm in leaving it on once the pipe work is bonded and the shower is RCD protected.

more habit now more than anything else!!

Sounds like a close shave in the work place.
It could have got nasty.

Pipework being bonded wouldn't really come into it. That's really just for keeping all metal at equal potential in the event of failed neutral outside house, type events.

RCD is for protection of someone in the shower, during which time the switch is on anyway, so leaving it on while not in use, the RCD won't be doing much.

I suppese the RCD might help isolate it should a fault develop in the unused shower alright, while the isolator is on.

The problem area of leaving shower isolator on might be with priority units, person goes to use shower, won't come on, and they forget to turn it off before leaving.

A simple relay wired like a DOL starter with start and stop buttons solves that though. They should be part of a shower setup from manufacturers. Simple to do, and effective.

Danny Mulcahy

Bruthal wrote: »

I suppese the RCD might help isolate it should a fault develop in the unused shower alright, while the isolator is on.

Yes thats my point.
Granted its all in theory if things go that badly wrong but accidents in theory are what the safety regs are built on. that would be why I mentioned bonding to even though I was kind of veering off topic

whizbang

Can over tightening a screw cause any danger electrical wise

If its a good quality terminal, the screw can cut through the wire end, or damage the wire beyond useful.

tomdempsey200

i was looking for info on thermal insulation
first time i saw that ecssa did actually suggest using the remote contactor instead of local isolator

weird that they would think that's ok
http://www.voltimum.es/files/ie/others/A/200709186888200709182020200709189222210summer2007.pdf

Bruthal

tomdempsey200 wrote: »

i was looking for info on thermal insulation
first time i saw that ecssa did actually suggest using the remote contactor instead of local isolator

weird that they would think that's ok
http://www.voltimum.es/files/ie/others/A/200709186888200709182020200709189222210summer2007.pdf

Definitely is not right to use that method as proper isolation.

tomdempsey200

Bruthal wrote: »

Definitely is not right to use that method as proper isolation.

yes ..in fact it's a bad idea altogether to suggest it