Shower fitting head scratcher

Discussion in 'Electricians' Talk' started by MikkDesign, Mar 25, 2021.

  1. MikkDesign

    MikkDesign New Member

    So I am trying to replace a 9.5kw shower that had a burnt out neutral connection on the load terminal on the isolator switch and was just generally old and past it’s best.

    I’ve replaced the switch with a brand new 45a and replaced the 10mm cable from the switch to the shower but left the existing 10mm cable from the switch to the fuse board as it’s in the walls running the length of the house.

    Problem I am having is when I make it live, the isolator switch is lighting up and the shower power light comes on. However, when I turn the shower to the on position the power light goes off and the light on the isolator switch goes off also.

    The rcd (40amp) doesn’t trip, when I turn the shower back off again the light on both the shower and the isolator switch comes back on.

    I’ve double checked that the cable from the fuse board is going into the feed and the shower is wired to the load as well as into the correct terminals and everything is as it should be.

    I have tried two switches to eliminate a faulty switch, two showers to eliminate a faulty shower unit and tried all this in two different rcd’s.

    So, this leaves me with the only thing in the system that is original and potentially faulty is the cable from the fuse board to the isolator switch.

    What I can’t understand is, if it is this cable, a) why I’m still getting power to the shower (albeit until I turn it to the on position), b) why turning the shower to the on position is causing the isolator switch light to go off.

    Any answers to the above and what I need to do to rectify the problem would be greatly appreciated. (“Call an electrician” will not be appreciated ha)
  2. AnotherTopJob

    AnotherTopJob Screwfix Select

    Sounds like the cable isn't capable of providing the high current required.

    You say the neutral was burnt out, I would look further down the cable for heat damage.
    Last edited: Mar 25, 2021
    rogerk101 likes this.
  3. MikkDesign

    MikkDesign New Member

    Apologies, I have said rcd when I meant mcb
  4. MikkDesign

    MikkDesign New Member

    Neutral was burnt out on the load terminal which cable I have completely replaced if that makes any difference?

    Is it possible for an old cable to deteriorate so that it provides some power but just not enough to run the appliance?
  5. terrymac

    terrymac Screwfix Select

    Do you have any testing equipment ? Twin probe voltage tester ,or a multimeter ?
  6. MikkDesign

    MikkDesign New Member

    i can get my hands on one easy
  7. The Happy Builder

    The Happy Builder Screwfix Select

    It sounds like a high resistance fault within the circuit, probably on the neutral terminals at the consumer unit or into the switch.

    I am guessing that when you turn the shower on the voltage is the same on the live and neutral, so the lights won’t light up.
  8. terrymac

    terrymac Screwfix Select

    Measure the voltages at switches feed ( supply) terminals ,between the following conductors...
    Live to Neutral.
    Live to earth.
    Neutral to earth .
    And the same again at the shower main terminal block.
  9. Bazza

    Bazza Screwfix Select

    When you fitted the new switch, did you cut the cable back to new bright copper?
  10. Alan sherriff

    Alan sherriff Active Member

    You sound fairly confident I would suggest taking the isolator out of the equation just a couple of large connectors and try again sounds like something is sinking the voltage only leaves consumer unit connections and the shower unless there are joints along the he cable run or damage
  11. MikkDesign

    MikkDesign New Member

    so feed;

    Live to neutral - 175
    Live to earth - 247
    Neutral to earth - 64

    So, armed with that knowledge, I went back to my fuse board and connected the neutral to a different busbar and hey presto, all is well!!!

    On a side note, you get what you pay for with cheap triton showers! ‍♂️
  12. Bazza

    Bazza Screwfix Select

    How did the neutral move itself on to the wrong bus bar?
  13. Bazza-spark

    Bazza-spark Screwfix Select

    And why are you not getting the RCD tripping?
    Philip Hyde likes this.
  14. Philip Hyde

    Philip Hyde Screwfix Select

    Yeah Like Bazza says How come you've moved the neutral but the RCD isn't tripping. Needs further investigation.
  15. PaulBlackpool

    PaulBlackpool Screwfix Select

    Only DIY but I think a insulation resistance test on the cable from the CU to the isolator is needed.Could rodents have got at it?
  16. MikkDesign

    MikkDesign New Member

    The shower was disconnected completely from the CU previously whilst doing some other wiring as it wasn’t in use. When I’ve reconnected it I’ve used the same RCD but connected to a different busbar most likely.

    At no point has either RCD I have connected it to tripped. Given it was a neutral connection problem at the CU am I right in thinking that I wouldn’t expect a trip anyway?
  17. Bazza-spark

    Bazza-spark Screwfix Select

    If you have a phase - neutral imbalance the RCD should trip.

    The fact neither have suggests you have issues that need to be investigated as a matter of urgency.

    Unless you have the appropriate test gear to check the correct operation of the RCD's and can carry out the appropriate tests I suggest you get a sparky in asap.

    Remember as well, water and electicity do not mix!
  18. The Happy Builder

    The Happy Builder Screwfix Select

    There should not be a neutral bar in the consumer unit that you could connect the cable to and get those test results.

    It is possible that there are two neutral bars that could be linked and the link has been removed which you connected to, but then I would expect the live to neutral to be around zero and neutral to earth 247 volts.

    You have made the shower work, but I have serious doubts about the safety of your electrical installation.

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