Scorched Neutral on shower isolation switch

jodaw

Would appreciate any input on the following. Shower stop working today and removed the isolation to find one of the neutral wires scorched. The switch is always used to switch off power to shower when not in use.

However sometimes kids would not turn off shower switch and turn the shower off direct from isolation switch itself.

There is also a crack it the plastic part of the switch where the neutral concerned is connected to the switch.

Any input as to if this is a damaged switch or something more serious? Shower has never tripped out.

Doolittle51

Loose connection. Replace the switch, strip back cable insulation until you have fresh copper & insulation. If that can't be achieved, replace the cable. It's a job for an electrician really.

2011

^^^ Agree 100%

Don’t use the shower until this is fixed. It would be best to switch the circuit off at the distribution board.

I would replace the switch with the larger type (like a cooker switch) with a quality make such as MK or Crabtree.

jodaw

Have a switched around somewhere. Need to have a look at it because it is a chinese one that is nicer to look at but always thought it look a bit flimsy.

Higher quality one would do a better job.

Doolittle51

You can't just throw any old switch in there. It needs to be rated appropriately. As I said before, it's really a job for a qualified electrician. If you don't know what you're doing, you will cause a fire, it's that simple.

2011

BTW it looks like the earth cable is not connected in that switch.

naughtysmurf

The Crabtree switches are good quality are easier to wire & fix, I'd replace with one of those, get the connections as tight as possible, we don't operate the switch daily, it shortens the life, only use it if I wish to isolate the shower.

jodaw

2011 wrote: »

BTW it looks like the earth cable is not connected in that switch.

Earth is connected at back box? Is that correct?

Bruthal

No earth onto switch terminal. Should be a double size switch, fitting a single size for shower cables was making life awkward even if 6 square.

No bushings or similar on steel box for cable entry.

Lose connection the likely cause, may have loosened more, over time. Switching on and off regularly, particularly under load, would`t help.

2011

jodaw wrote: »

Earth is connected at back box? Is that correct?

That’s good, I couldn’t see that. This should also connect to the switch.

jodaw

Here is a new switch that was never installed. Rated 45A

Is the earth on the metal backbox sufficient? Or is best practive earth terminal on switch?

Switch has not been changed/removed since house was built from new.

John.G

Bruthal wrote: »

No earth onto switch terminal. Should be a double size switch, fitting a single size for shower cables was making life awkward even if 6 square.

No bushings or similar on steel box for cable entry.

Lose connection the likely cause, may have loosened more, over time. Switching on and off regularly, particularly under load, would`t help.

I've wondered about that a few times, ie, switching the shower on/off from the isolation switch. Obviously, it should be treated as such but will often be used as above. If it's suitably rated at 45/50A? (for a 9kw shower) and the terminals have been properly tightened then is there any reason why that switch shouldn't last for a very long time even if it is "improperly" used for switching the shower on/off?.

What I am getting at, is, are there different quality contacts in a switch used for isolation purposes vs switching the load on/off?.

2011

If a circuit is supply a large load such as a 9 kW shower and the isolator is switched then an electric arc will occur across the switch contacts. Every time this happens it will cause some damage. Although this damage is small it gradually accumulates, eventually causing the isolator to fail. Some wear and tear (although far less) also occurs when this switch is operated under no load condition. This damage manifests itself as resistance which gradually leads to more and more heating within the switch can eventually result in what we see in this example.

Therefore, in my view the isolator should only be used to switch off the shower when maintenance is being carried out on the shower unit itself and at no other time.

Bruthal

John.G wrote: »

I've wondered about that a few times, ie, switching the shower on/off from the isolation switch. Obviously, it should be treated as such but will often be used as above. If it's suitably rated at 45/50A? (for a 9kw shower) and the terminals have been properly tightened then is there any reason why that switch shouldn't last for a very long time even if it is "improperly" used for switching the shower on/off?.

What I am getting at, is, are there different quality contacts in a switch used for isolation purposes vs switching the load on/off?.

The contacts are the same more or less, just bigger in higher load switches. Of course, there are different quality contacts in all types of switches. Just that switching high loads causes pitting, and that in turn reduces the contact area for carrying the high load.

Shower isolators wouldnt usually be switching the load even if switched off after every shower. Wall switches would probably last a long time doing this.

Pull chords though, are not as mechanically reliable as the wall switches imo.

Copper also compresses and over time, can become slightly more loose in what was initially a reasonably tight connection, and switching regularly, could loosen the connections more with the snapping action of wall switches. Whether this happens or not, im not sure, but it is a possibility.

John.G

Interesting, the shower contacts themselves, rated, I think, at 27A each, are switching their loads in/out multiply times/day but I have rarely heard of them failing (Sleeper12 will soon inform), these have a switching margin of approx. 40% as they are switching ~ 20A, whether this makes any difference or not.
Also, I think the double pole contacts on my Hager RCBO don't switch together, I think one opens before the other to break the load and makes first when it is switched back in, there must be some reason for this, if true.

jodaw

Connecting up the new switch. It is rated same as switch that came off. Top neutral in photo cable cut back and strip. Bottom neutral slight cables have slight residue but copper looks good.

Both cable earthed on the backbox as per photo. In new build circa 2007, original switch wire like so and not connection to earth terminal on the switch.

Should i definitely link an earth from terminal on switch back to backbox or would original wiring config work fine either way?

Bruthal

John.G wrote: »

Interesting, the shower contacts themselves, rated, I think, at 27A each, are switching their loads in/out multiply times/day but I have rarely heard of them failing (Sleeper12 will soon inform), these have a switching margin of approx. 40% as they are switching ~ 20A, whether this makes any difference or not.
Also, I think the double pole contacts on my Hager RCBO don't switch together, I think one opens before the other to break the load and makes first when it is switched back in, there must be some reason for this, if true.

A lot of the switch problems are probably poor install to begin with.

10 square into these switches wont be helping.

No real reason for one contact to open before the other in a single phase breaker, but there would be good reason for the N to close first and open last in a 3 phase one. Perhaps this mechanism is also used in single phase devices.

salmocab

Yes earth the switch

jodaw

Thanks all. New switch installed. New additional earth from switch added.

Its a sexy looking switch and now i know where the fish smell was coming from after i got out of shower.

Will keep close eye on it going forward.

Would something like that going on with the neutral wire not cause the RCBO to trip? Never did

Risteard81

2011 wrote: »

^^^ Agree 100%

Don’t use the shower until this is fixed. It would be best to switch the circuit off at the distribution board.

I would replace the switch with the larger type (like a cooker switch) with a quality make such as MK or Crabtree.

MK is not a quality make anymore.

salmocab

You haven’t sleeved your Earth from the look of that, that needs sorting.

jodaw

salmocab wrote: »

You haven’t sleeved your Earth from the look of that, that needs sorting.

Thank you for your help. Yes i will get that sorted as soon as i can. Dont have any sleeve on hand

Doolittle51

The insulation on one of the neutrals is damaged, exposing some bare copper...

Bruthal

Pinch damage visible on the neutral in one photo. It just doesnt look like craftmanship, the original install. Its typical,, quick as we can, in and out, or, a diy job.

No way i would put that switch back up with cable cores through raw steel knockout holes.

2011

+1

Shoddy workmanship. If this were in my home I start by checking that everything in the distribution board is ok, right etc.

Note: I am qualified to do this.

aido79

Bruthal wrote: »

Pinch damage visible on the neutral in one photo. It just doesnt look like craftmanship, the original install. Its typical,, quick as we can, in and out, or, a diy job.

No way i would put that switch back up with cable cores through raw steel knockout holes.

Exactly. It's rough. Looks like there was too much cable left in the box behind the switch and that's the reason for it being pinched and most likely the reason for the loose neutral.

Hintel

Personally I wouldn't be too happy to have family using that shower now

Bruthal

Hintel wrote: »

Personally I wouldn't be too happy to have family using that shower now

Plenty of shower installs have switches not too well installed.

Hintel

Bruthal wrote: »

Plenty of shower installs have switches not too well installed.

There's at least 3 issues visible

jodaw

Thanks for all input guys. The electrical or all installations on house always left a lot to be desired. I think i will just isolate circuit a distribution board a get a sparks in to look.

I just want to make sure all is sorted. So issues to be sorted

- earth from switch to be fully sleeved
- pinched neutral to be sorted
- no cable cores through steel knockouts

Would this sort it?

Bruthal

jodaw wrote: »

Thanks for all input guys. The electrical or all installations on house always left a lot to be desired. I think i will just isolate circuit a distribution board a get a sparks in to look.

I just want to make sure all is sorted. So issues to be sorted

- earth from switch to be fully sleeved
- pinched neutral to be sorted
- no cable cores through steel knockouts

Would this sort it?

Cables through steel knockouts with grommets or bushings fitted.

Pinched neutral is in photo 2 where you can see insulation is damaged and copper is visible. Looks like it was possibly against the steel edge of the knockout hole when the neutral was longer before you cut to clean up.

The cores will be pressed against the edges of the steel holes with switch fitted.

If it was touching the steel box if its properly earthed, it should have tripped the RCD when the shower was on, assuming the shower has one in the fuseboard.

jodaw

Bruthal wrote: »

If it was touching the steel box if its properly earthed, it should have tripped the RCD when the shower was on, assuming the shower has one in the fuseboard.

Then it looks like it was never properly earthed. Has rcd in distribution. Shower never once tripped it.

No backboxes in house have any sort of grommet

Bruthal

jodaw wrote: »

Then it looks like it was never properly earthed. Has rcd in distribution. Shower never once tripped it.

No backboxes in house have any sort of grommet

Its possible the neutral copper never touched the box or anything earthed.

Bare steel holes with cables through is a real cowboy effort imo. It is not unusual.

jodaw

Bruthal wrote: »

Its possible the neutral copper never touched the box or anything earthed.

Bare steel holes with cables through is a real cowboy effort imo. It is not unusual.

Very cheapo effort in whole house really. Switches and backboxes crooked and any i have seen would have no grommets.

One thing that pisses my off is there were never any circuits ran to hotpress, so an immersion or pumped shower would need a whole new circuit run back to fuseboard

Tuco88

I don't know why fellas don't just put fly leads on all the back boxes/metal clad boxes before installing. Thats what we used to do.

Should the link between the Shower Isolator switch and backbox be the same C.S.A as the line conductor?


Personally I wouldn't really see an issue with 2.5mm^2, as regards on a technically point of view for an Earth fault path should it be the same? Be all is you couldn't possibly get 3 into 1 terminal anyway..

Could he repair the cable insulation with a heavy heat shrink.

Risteard81

Tuco88 wrote: »

Personally I wouldn't really see an issue with 2.5mm^2, as regards on a technically point of view for an Earth fault path should it be the same?

It would only need to be able to sustain the fault current until disconnection occurs (as per the adiabatic equation). So 2.5mm^2 would be absolutely fine for a 6mm^2 cable (or say 4mm^2 for a 10mm^2).


It simply isn't possible to connect 6mm^2 or 10mm^2 conductors to the backbox (without drilling and tapping), and as you point out would never fit in the terminals on the accessories anyway.

Sam Quentin

Can the experts also advise: it's just not good practice turning off shower by main terminal, slamming the shower into a no power lock down instead of turning the shower off with its intended stop button couldn't be good,.am I right!?

Hintel

Sam Quentin wrote: »

Can the experts also advise: it's just not good practice turning off shower by main terminal, slamming the shower into a no power lock down instead of turning the shower off with its intended stop button couldn't be good,.am I right!?

Yes those isolators are best left on all the time anyhow

They're too troublesome when used all the time

2011

I agree with Hintel but, there are plenty of highly qualified and experienced professionals that take an opposing view.

Sleeper12

2011 wrote: »

I agree with Hintel but, there are plenty of highly qualified and experienced professionals that take an opposing view.

I understand your logic behind this but the Fire Officer now recommends the isolation switch be turned off after each shower. His logic is even if isolation switch needs replacing every year or two it's cheaper than repairs after a fire. This isn't a legal requirement. It's a comment he made after an unattended electric shower, turned off, went on fire.

John.G

And yet, while worrying about such trifles, I am quite happy to (legally) shower away merrily in my 14 year old Mira Sport with water spraying everywhere with my nose literally inches away from a 230V cable contained in a "shower proof" plastic box!.

Sleeper12

John.G wrote: »

And yet, while worrying about such trifles, I am quite happy to (legally) shower away merrily in my 14 year old Mira Sport with water spraying everywhere with my nose literally inches away from a 230V cable contained in a "shower proof" plastic box!.

Water resistant rather than waterproof. Hold the full flow of the water over the top of the cover & the RCBO might pop

Bruthal

Sleeper12 wrote: »

I understand your logic behind this but the Fire Officer now recommends the isolation switch be turned off after each shower. His logic is even if isolation switch needs replacing every year or two it's cheaper than repairs after a fire. This isn't a legal requirement. It's a comment he made after an unattended electric shower, turned off, went on fire.

He may as well recommend turning off the DB main switch whenever a house is left unattended too.

John.G

Sleeper12 wrote: »

Water resistant rather than waterproof. Hold the full flow of the water over the top of the cover & the RCBO might pop

My relation's shower would trip the RCBO once or twice a year, I found one of the front cover top securing screws wasn't fitted so I replaced it and the shower hasn't tripped since.

2011

Sleeper12 wrote: »

I understand your logic behind this but the Fire Officer now recommends the isolation switch be turned off after each shower. His logic is even if isolation switch needs replacing every year or two it's cheaper than repairs after a fire. This isn't a legal requirement. It's a comment he made after an unattended electric shower, turned off, went on fire.

The counter argument to what you have stated above is that a fire is far more likely to occur in the first place if the isolator is operated before and after the use of the shower. Although I accept the argument that replacing an isolator every year or two is not that expensive this ignores the fact that the fire that may occur due to the failure of this device is the real cost.

My next point is where does this end? Does the fire officer (or others sharing this view) only insist on this practice for the shower or does it extend to other fixed appliances? If not, why not? Surely only a consistent approach makes sense? In many homes fixed appliances typically include:

• Hob
• Oven
• Boiler
• Intruder alarm
• Immersion
• Zone valves

Also there are many devices that are left plugged in for years in homes up and down the country such as:

• Washing machine
• Tumble dryer
• Dish washer
• Microwave
• TV
• Satellite box

If all of the above are to be unplugged or their isolator switched off it would take at least an hour to leave the house each day:D

As I have already stated, I accept fully that there are differing opinions on this. That is why I made it clear in post #13 that what is stated is just an opinion (by using the words "in my view").

John.G

Does the isolator have to installed in close proximity to the shower or can it be installed at the main board?.

2011

John.G wrote: »

Does the isolator have to installed in close proximity to the shower or can it be installed at the main board?.

It should be local to the appliance it isolates. However there are specific requirements about how and where devices such as this are installed in a bathroom.

Frequently you will see these devices are installed just outside the bathroom.

Bruthal

John.G wrote: »

Does the isolator have to installed in close proximity to the shower or can it be installed at the main board?.

Its function is to isolate the shower to allow safe working on it. Down at DB doesn't do that.

To allow easier wiring of isolator beside showers it was recommended contactors be fitted at the DB and small control wiring up to isolator.

My opinion at the time this is not proper isolation. Very bad actually imo.

I think 10 square with 10 square earth is over the top as well.

John.G

Thanks, would/are you happy to carry out maintenance on a shower with say a pull cord isolator without switching out the RCBO or whatever as a extra precaution even though this wouldn't be considered a isolator as such.

Bruthal

John.G wrote: »

Thanks, would/are you happy to carry out maintenance on a shower with say a pull cord isolator without switching out the RCBO or whatever as a extra precaution even though this wouldn't be considered a isolator as such.

I would anyway. Sometimes the RCBO would be used, for example, changing the isolator.

The way regs are going, they might bring out an isolator for the isolator.


In industrial situations, locks would be used to keep circuits isolated. Domestic it is much easier to keep track of what is happening around the area.

2011

Yes, industrial installations are a very different animal. They require electricians with very different skill sets, which can often require specialist training.