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Scorched Neutral on shower isolation switch

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  • 22-04-2020 10:15am
    #1
    jodaw
    Registered Users Posts: 691 ✭✭✭


    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.


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    #2
    Doolittle51
    Registered Users Posts: 398 ✭✭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.


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    #3
    2011
    Moderators, Home & Garden Moderators, Technology & Internet Moderators, Regional East Moderators Posts: 12,596 Mod ✭✭✭✭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.


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    #4
    jodaw
    Registered Users Posts: 691 ✭✭✭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.


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    #5
    Doolittle51
    Registered Users Posts: 398 ✭✭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.


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    #6
    2011
    Moderators, Home & Garden Moderators, Technology & Internet Moderators, Regional East Moderators Posts: 12,596 Mod ✭✭✭✭2011


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


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    #7
    naughtysmurf
    Registered Users Posts: 3,263 ✭✭✭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.


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    #8
    jodaw
    Registered Users Posts: 691 ✭✭✭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?


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    #9
    Bruthal
    Closed Accounts Posts: 13,422 ✭✭✭✭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.


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    #10
    2011
    Moderators, Home & Garden Moderators, Technology & Internet Moderators, Regional East Moderators Posts: 12,596 Mod ✭✭✭✭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.


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    #11
    jodaw
    Registered Users Posts: 691 ✭✭✭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.


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    #12
    John.G
    Registered Users Posts: 3,514 ✭✭✭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?.


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    #13
    2011
    Moderators, Home & Garden Moderators, Technology & Internet Moderators, Regional East Moderators Posts: 12,596 Mod ✭✭✭✭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.


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    #14
    Bruthal
    Closed Accounts Posts: 13,422 ✭✭✭✭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.


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    #15
    John.G
    Registered Users Posts: 3,514 ✭✭✭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.


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    #16
    jodaw
    Registered Users Posts: 691 ✭✭✭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?


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    #17
    Bruthal
    Closed Accounts Posts: 13,422 ✭✭✭✭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.


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    #18
    salmocab
    Registered Users Posts: 11,366 ✭✭✭✭salmocab


    Yes earth the switch


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    #19
    jodaw
    Registered Users Posts: 691 ✭✭✭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


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    #20
    Risteard81
    Registered Users Posts: 2,567 ✭✭✭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.


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    #21
    salmocab
    Registered Users Posts: 11,366 ✭✭✭✭salmocab


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


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    #22
    jodaw
    Registered Users Posts: 691 ✭✭✭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


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    #23
    Doolittle51
    Registered Users Posts: 398 ✭✭Doolittle51


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


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    #24
    Bruthal
    Closed Accounts Posts: 13,422 ✭✭✭✭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.


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    #25
    2011
    Moderators, Home & Garden Moderators, Technology & Internet Moderators, Regional East Moderators Posts: 12,596 Mod ✭✭✭✭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.


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    #26
    aido79
    Registered Users Posts: 5,374 ✭✭✭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.


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    #27
    Hintel
    Closed Accounts Posts: 110 ✭✭Hintel


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


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    #28
    Bruthal
    Closed Accounts Posts: 13,422 ✭✭✭✭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.


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    #29
    Hintel
    Closed Accounts Posts: 110 ✭✭Hintel


    Bruthal wrote: »
    Plenty of shower installs have switches not too well installed.

    There's at least 3 issues visible


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    #30
    jodaw
    Registered Users Posts: 691 ✭✭✭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?


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    #31
    Bruthal
    Closed Accounts Posts: 13,422 ✭✭✭✭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.


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