Garage consumer unit trips off when switching off garage lights

Discussion in 'Electricians' Talk' started by Karl Taylor, Mar 25, 2018.

  1. Karl Taylor

    Karl Taylor Member

    ok thanks for that information . i try that test .
  2. Bob Rathbone

    Bob Rathbone Well-Known Member

    Karl, you did not mention the crackling switch earlier, it should not crackle, so it needs to be changed whatever you decide to do.
  3. JP.

    JP. Screwfix Select

    Can an arcing switch contact trip rcd?
  4. Bob Rathbone

    Bob Rathbone Well-Known Member

    It depends on the type of loads connected, the RCD will respond adversely to non symmetrical currents such as may be found in circuits that have arcing contacts. Change the switch, it's a couple of quid and half an hour of your time, take a photo before you start and identify all of the cables. If it does not fix it you are only out of pocket by a few quid. If it does fix it, then you have saved yourself a considerable sum.
  5. JP.

    JP. Screwfix Select

    Yes agree. Whatever happens the switch should be changed. I suppose if you look at an arcing switch output on a trace then spikes of varying amplitude would be generated - wether this could trip an rcd I haven't got a clue. This begs the question - can rcd's trip if they sense transients of varying magnitude?
    Last edited: Mar 27, 2018
  6. unphased

    unphased Screwfix Select

    You said "The only other thing i can say is that some times when i was switching the lights off from the front double switch i could here a slight crackle noise as i switch the light off and then the rcb would trip."

    Apologies, I missed that snippet of information. There could be a clue there. Please do check the switch.
  7. Karl Taylor

    Karl Taylor Member

    thanks all that have commented , very helpfull. i do that first and get a new switch. very suprised that mk logic stuff might go faulty but again ist all mass produced and worked ok on install so any think could cause it to fail , looks ok as new but for a couple of quid i get one on way home tonight and have a look tomorrow . thanks
  8. Bazza

    Bazza Well-Known Member

    MK is not the company it once was. Mostly made in china now.....

    Re crackling switch. Fluorescent lights have a largish start up current, and you may get a crackling at switch on/off. But do change the switch and prove everybody wrong - you know you want to!
  9. Karl Taylor

    Karl Taylor Member

  10. JP.

    JP. Screwfix Select

    Is it possible that a back emf is being produced on florrie switch on which imparts a trip on over sensitive rcd?
  11. Lectrician

    Lectrician Screwfix Select

    A lost earth can cause this type of fault, as can an insulation fault on the supply side of the RCD.
  12. Karl Taylor

    Karl Taylor Member

    A lost earth can cause this type of fault, as can an insulation fault on the supply side of the RCD.

    these kind of faults i will need to get a electrician in to test the system then as i wouldnt know how to check apart from the obvious loose wires etc .....

    i try a new switch and then disconnect one light at a time to narrow it down ........then it will be a call to a electrician as these faults i wouldnt know........
    A lost earth can cause this type of fault, as can an insulation fault on the supply side of the RCD.
  13. Karl Taylor

    Karl Taylor Member

    Well changed the switch. crackle sound gone . Switch a lot more accurate in pressing now.

    But switched lights on a few times and off again and yep sure enough the rcd has tripped out.

    I now disconnect each one of the lights tomorrow in turn and go from there.
    Hopefully it will be a light fitting thats faulty... .....
  14. Karl Taylor

    Karl Taylor Member

    Isolated first flourecent light. Result doesn't trip. So i thought.
    Reconnected and then isolated second .it trips out so thought this light fitting .
    Nope .

    Tested again now tripping on first light fitting when second one disconnected.
    So its not the light fittings??

    Carnt be both?

    Must be some fault inside the fuse box??
  15. PhilSo

    PhilSo Active Member

    Does it trip with all the light fittings disconnected?


    Found your diagnostic report confusing. That might just be me though. :oops:
  16. Karl Taylor

    Karl Taylor Member

    Disconect light 1
    Switch light switch on for both lights
    Switch light switch off for both lights, switch off light 1. Then switch off light 2.
    Rcd tripped

    Reconnected light 1.
    Disconnected light 2.

    So in theory the rcd shouldn't trip. As its just tripped on light still connected.

    Switch light switch on and off for both lights.

    Rcd trips.

    Could both new light fittings be faulty? Or is the rcd faulty?

    Time to get a electrician in i think to test it as i carnt think what else to do apart from change rcd.
    But i have had the cover off after isolating garage electrics and i carnt see any thing loose or burnt etc so what now?
  17. Karl Taylor

    Karl Taylor Member

    So how can this be found? I need a electrician in now i think.
  18. Sparkielev

    Sparkielev Well-Known Member

    Take both lights down and fit 2 standard pendants then you will know if the lights are faulty
    PhilSo likes this.
  19. Karl Taylor

    Karl Taylor Member

    What the chances of both light been faulty ???
  20. Sparkielev

    Sparkielev Well-Known Member

    Hard to say without seeing the fittings are they old ?

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