Electric shower wire burning out!!

Discussion in 'Electricians' Talk' started by AshMiah, Jun 6, 2015.

  1. AshMiah

    AshMiah Member

    Hi Guy's, revising an old issue here…

    I've got an 8.5kw electric shower, last December I changed the circuit breaker from a 16A to a 32A, hoping it would resolve the issue of the live wire (6mm thick) overheating and melting the plastic around it.

    Unfortunately I was wrong (not the first time i've been wrong), the red wire into the leed port has burnt out just the same way before I had changed the circuit breaker to a 32A?

    I've been replacing the switch, a 45A double pole. Every time I do so I lose a little bit of the wire, and i'm fast approaching the end before theres no more slack.

    I have been told in the past, an 8.5kw electric shower should really have a 10mm wire, but this is not really an option I have unless I tear the walls down.

    Here's what I suggest, to alleviate the problem of running out of wire and upgrading to a 10mm wire, can I attach a 10mm wire to the existing 6mm wire with a connector?

    Whats the dangers of doing this?

    Or some advise on what I can do pls - hopefully it doesn't include buying a 9.5kw shower!!

    Thx as always guys.
  2. unphased

    unphased Screwfix Select

    Hi Ash

    I doubt that the cable is burning due to the loading. Its 99% certain to be poor termination of the cable. Shower accessories are always burning out through loose terminations and if you are continually replacing the switch that is the reason.

    The remedy is to pull out some slack in the cables (there is usually enough to pull) buy another good quality 45A switch or 50A and make sure you terminate the wiring fully in to each terminal and do it up very tight.

    32A breaker on a 6mm2 cable is perfectly adequate. A 30mA RCD is also required.

    FatHands and AshMiah like this.
  3. AshMiah

    AshMiah Member

    Thx unphased.

    This is the switch i've been using for the past few years from B&Q, can you recommend any other better ones?

    Not sure I have that much slack left, but will re-check.

    I had a sparky come in last time to change the breaker to the 32A and thats when he also fitted the new switch, don't know what to say, but he did look like he was tightening it as much as possible?

    Nexus 1-Gang 45A Black Nickel Effect Cooker Switch
    Product code: 5050765023337

    Link to the page.
  4. Mr. Handyandy

    Mr. Handyandy Screwfix Select

  5. seneca

    seneca Screwfix Select

    That switch should be fine. As Unphased said your problem has almost certainly been caused by loose connections.
  6. Mr. Handyandy

    Mr. Handyandy Screwfix Select

    One thing I never understood about the design of terminals, is how the screw never fills the hole for the wire. In the case of stranded solid wires, screwing it down can allow single strand to go up the side of the screw and not get tightened down. Then, what with the thickness of the cable needing a bit of force to get the socket back on, that can move the tightened wire and maybe misplace the tightened wire again.
    You can sometimes see this for yourself, tighten the screws, push the socket in, pull it out, test the tightness. Possibility it is not as tight as you first did it.

    Mr. HandyAndy - Really
  7. Mr. Handyandy

    Mr. Handyandy Screwfix Select

    ....and why is no-one pointing out the errors in Ashmiah's thoughts in regard to the size of the MCB making any difference, and adding 10mm² to 6mm² the same ? And a check that the switch should be outside any zones etc

    Mr. HandyAndy - Really
  8. unphased

    unphased Screwfix Select

    Good morning Ash
    That switch, in my opinion, is too small in size for terminating the wiring. The wiring will be too squashed behind it. I would suggest changing the switch for one like this:
    You would also need a nice deep box, preferably one like this:
    If the wire has become too short then you can extend it with yellow through crimps but this may be outside your scope if you don't have the correct tools.

    In this instance I would get in a pro and point out the issues you have been having and he will advise on best course of action.

    NorbieG likes this.
  9. peter palmer

    peter palmer Super Member

    Nearly all the shower switches I have seen burned out have been the ones the customer has switched off after every shower.
  10. AshMiah

    AshMiah Member

    This is probably ignorant of me, but in an attempt to keep the existing whole in my plaster board (86mm x 86mm) where the switch sits, and to minimise my efforts (really not to create a bigger whole!) as there is room above and below the back of the switch once in the wall. Can I use this switch which really has the same port distances of the bigger one you provided except the earth wire ports are much spaced out?

    I have a plastic back box of 47mm, but the entire back and most of the sides have been cut out to let the wires in without too much hassle. Directly behind the switch wall is the shower room, so won't be able to fit a mettle back box unfortunately, not sure if thats makes any difference.

    I feel I need to provide my history behind my shower problems, so heres a little more insight.

    The switch once newly installed will last typically 9-12 months, average usage, say around two showers a day, but at times for extended periods, 20-30 mins!
    I will notice the switch heating up after around 6-8 months of usage, even if the shower was on for five minutes.
    There are two settings on the Triton 8.5kw shower, most of the year (because it's freezing out side) its on setting two, the higher setting.
    If the shower is operating on setting one (lower setting) the switch hardly heats up al all, warm at best. I am able to use the shower at the lower setting even if the shower switch is nearing the end of its life 9-12 months without it cutting out.
    The live feed wire is the only wire to burn out, all the other wires for the switches I have changed are always fine.

    Here is the most puzzling fact. I have the exact same electric shower on the second floor which is almost twice the distance from the fuse box then the one in question. It operates a pull cord, and has never caused any problems in the past 12 years (we have changed showers in that time by the way).

    Hope that provides a better insight.

    One other question, when I expose the copper wires, I am supposed to twist the strands until they are interlocked as much as possible right?

    Thx for all your advise guys!!
  11. JP.

    JP. Screwfix Select

    No you do not twist the strands - you flatten them. Same as when fitting 16/25's into DB main switch etc tunnels.

    If you don't do this then there is a good chance of fizzing tunnels 'n' stuff
    FatHands and unphased like this.
  12. unphased

    unphased Screwfix Select

    Hello again Ash. No you should NOT twist the wires. That could be the reason they are loosening over time. The professional way to tighten the terminal is to have approximately 10mm of the copper strands cut nicely square at the ends and STRAIGHT (not twisted) so that they go snuggly and completely in to the switch terminal. Then you tighten up the screw nice and tight, push the wire in to the back box, CHECK the tightness of the screw again then push the switch in to position and secure it.

    As regards getting a larger switch you should consider this. It is very easy to cut plaster board and you can get bigger plasterboard boxes to suit like this:

    I suspect that you may have stripped and cut the wires to the point where they will be straining on the terminals now so it really would be a good idea to get them lengthened if you have no more slack to pull through. One advantage of cutting in a new bigger switch is you may be able to cut the hole towards the two wires thus lengthening them.


    Last edited: Jun 7, 2015
    FatHands likes this.
  13. sorethumb

    sorethumb Member

    I had this problem on a Triton shower. Seems incredible that they would fit flimsy push on 'Lucar' style connectors to handle a heavy current. I substituted heftier spade terminals which could be bolted together.
  14. AshMiah

    AshMiah Member

    Thx guys, can't stress how useful this forum is, particularly when you have legends like Unphased!!

    Quick dumb question - apologies.

    1. It will make no difference to have the larger switch placed horizontally, this is the only way I can get some length back?

    Also, I'm guessing the link of the stainless steel switch from Ukelectricalsuppliers is a very good one compared to the previous one from Screwfix because...?

    Will attempt to replace the switch this weekend, this time flattening the copper wire.
    Will it be a problem if I was to insert some of the insulation with the 10mm coper wire I will expose into the terminals?

    Thx guys
  15. unphased

    unphased Screwfix Select

    Hi Ash. No it won't make any difference to have the switch horizontal. I just used the link as an example of an alternative switch. That one is from Click Deco range. I just thought you wanted a decorative one rather than white. The size of the switch is more important.

    If you ensure that the screw in the terminal makes good contact with the copper that will be fine. It is usual to have a short amount of insulation entering the terminal so no copper is exposed within the switch.

    Good luck! Let us know how you get on.
    FatHands likes this.
  16. NorbieG

    NorbieG New Member

    I was Googling for help when I came across your thread about the same issue with my electric shower switch - wire burnt out. I must say; it's everything I needed to know.:) I'm going to buy the BRITISH GENERAL 900 SERIES 45A 2-GANG DP COOKER SWITCH and the APPLEBY GALVANISED STEEL KNOCKOUT BOXES 2G 47MM. And yes, I'm going to flatten the copper wires this time.

    Nice one, guys! ;)
  17. NorbieG

    NorbieG New Member

    Is the 'British general 45a 1 gang double pole cooker switch large plate white/91193' suitable to fit in the barth room, or, should it be fitted outside of the bathroom?

    I've bought the 'Appleby 2 gang 47mm dry lining box' instead of the 'Appleby galvanised steel knockout box' because it has to be fitted in the plasterboard.
    Last edited: Feb 13, 2020
  18. peter palmer

    peter palmer Super Member

    Don't put the switch inside the bathroom, they are usually on the wall outside somewhere near the light switch or inside the airing cupboard. You could possibly fit it inside the bathroom if its more than 600mm from the shower or bath (not a wet room) but I don't recommend it. You are right to buy the double size switch as opposed to a single one, a client has just bought 2 single size 45A chrome switches for me to fit to two showers, absolute ***** of a job to get 2 x 10mm cables inside a single box, I actually broke the first fast fix box in half trying to get it back.

    BG should be ok, just don't buy one made by LAP, the ones with the twin terminal screws are the best though but I can't remember which make does them.

    Meant to add, if this is a new install done by you then it should have building control notification as a new circuit, and make sure its RCD protected / main bonding done etc, don't want to kill anyone now do we.
    NorbieG likes this.
  19. Mr Rusty

    Mr Rusty Screwfix Select

    thread archaeology again
  20. peter palmer

    peter palmer Super Member

    For once its not a troll though this time, its soemone asking a genuine question.
    Rulland likes this.

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