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

    Hi all. Just after some advice please just in case i can fix this.
    On a few occasions i have come to switch my internal garage light off it has caused the garage consumer unit main breaker to trip.
    I have the lights on a duel circuit, i can switch them off and on at either end of the garage. I have six lights in total on six switches at the back of the garage and two at the front of the garage.
    It doesnt matter which light i switch off and doesnt matter if i am at the front or back of the garage. The garage consumer unit trips out.
    Light switch at front of garage i can switch two lights on, one at front of garage and one at back if garage. The switches at back of garage can switch these two lights on and off as well as the other 4 lights.
    The lights are fluorescent single tubes.
    The fuse boxes have been installed by a qualified electrician and tested on install.
    Now out of guarantee .

    I suspect its just a power surge as doesn't do it all the time? Or is there something wrong or do i need higher values of mcb in the fuse box in the house or is it a faulty garage rcd unit?

    House supply fuse to garage is a mcb rated at 40. This does not trip out.

    Garage fuse box rcd says 63A 30 ma 240volt
    This is what keeps tripping out. the lights mcb on this unit does not trip out.

    I have tested the garage rcd by pressing the test button and it works fine .

    Think might have to get electrician out if not a simple fault? any advise welcome.
    Last edited: Mar 26, 2018
  2. Comlec

    Comlec Well-Known Member

    A pic of the garage fuse box might help get better answers
  3. Karl Taylor

    Karl Taylor Member

    Can not post photos at the minute as saying this server is saying photos are too large for this server to process. I have them on my phone.

    Both consumer units are 17th edition units.
    Both MK consumer units. Garage unit is a 6 way garage unit with six seperate mcbs operating different cicuits in the garage. The lighting cicuit is protected by a B6 mcb

    The rcd inside the garage unit is a 63a 30ma breaker.
    Last edited: Mar 26, 2018
  4. Comlec

    Comlec Well-Known Member

    If the RCD trips it is because there is a fault to earth. This can be from the live or the neutral. I would check for damp in the fittings, switches and any junction boxes. Next stop would be check the light fittings.
  5. Karl Taylor

    Karl Taylor Member

  6. Karl Taylor

    Karl Taylor Member

    The picture above is the unit in the garage.

    The six independent light switches at the back of the garage are inside waterproof boxes. 3 in total so as to make 6 light switches if that makes sense.
    The light switch at the front of the garage on the inside wall is just a normal two way rocker switch.

    So this could be damp inside?
  7. Karl Taylor

    Karl Taylor Member

    I have 3 of this type of switch at the back of the garage, to try and make it clearer of what type of switches BGE_WPB42.jpg i have .
    At the front of the garage is just a normal two gang plastic switch.
  8. fire

    fire Well-Known Member

    If they are the fluorescent tubes, the capacitors can be feeding back on the circuit tripping out your breakers. It is very common those light fittings end up leaking current to ground so much so even the housing of the light can become live.
    You need to test the circuit completely, insulation test as well as check all the switches. Corroded terminals and connections can cause issues, an insulation test and resistance check can determine the fault.

    Inside the lights is a transformer a HV transformer so be careful. The transformers can fail and cause a ground leakage, when you power off the light the stored energy as in it's capacitance has no where to go but down the earth wire to ground which trips the breaker.

    It does need testing but most likely it is a faulty light fitting/transformer, starter or something along them lines.

    If you need change the lights then replace them with LED type instead. Fluorescent lighting sucks.
  9. JP.

    JP. Screwfix Select

    I've got a couple of 4 ft florry units in my loft Mr F (I think there 4ft) problems? Nope very good light output for the wattage and colour is good.
  10. fire

    fire Well-Known Member

    When they work they work, it is when they fail you get problems. Some of these light fittings are built well and work fine but some of these cheap made in china ones don't last and are more prone to fail than others i have found.
  11. Bob Rathbone

    Bob Rathbone Well-Known Member

    Do the lamps have electronic or inductive ballasts. It is unusual for the RCD to trip on switch off, normally they trip at switch on for reasons stated above, such as damp. Has it always been like this, have any additions been made. The cause could be anything from a fried mouse to a faulty RCD. Need to get a good electrician in.
    Karl Taylor likes this.
  12. unphased

    unphased Screwfix Select

    I would be tempted to replace both florescent light fittings with new LED batten fittings, similar shape but much better energy efficiency. I agree with fire, it is likely to be one of the fittings failing that is causing this. Very unlikly to be a wiring fault. Something like this would be perfect.
  13. JP.

    JP. Screwfix Select

    Hmmmmm view good reviews Un
  14. Karl Taylor

    Karl Taylor Member

    Been having a look tonight. This is what i have done as dont have access to testing equipment so think next to get a electrician out:

    Have checked two way double switch at front of garage for moisture etc . All fine.

    Have checked all the light fittings. All wires secure.

    The 3 double weather proof 2 way sockets at back of garage i have not checked internally yet.

    Have managed to get it to trip the rcb in garage several times by operating the frint garage rocker switch om both sides switching the two lights off either by switching the front light off then the back or by switching the back light off first then the front one.

    I then did the same again with the 3 weather protection switches at the back of the garage.
    Result is only when i switch the two suspect lights off either by first switching the front one off or the back on it trips the rcb in the garage. When i switch the other four garage lights on and off the garage rcb does not trip.

    My thoughts are it must be either a fault on both flourecent light units , but they are not that old or may be the front double switch but again that is not that old.
    Its not a cheap make either. It was a mk logic switch.

    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.

    Would a faulty rocker switch at the front of the garage cause the problem even if i switched them off from the insulated switch at the back of the garage? I know its on the same circuit but would this cause the fault still?

    Think next cause of action is to get a electrician in
  15. nigel willson

    nigel willson Well-Known Member

    Would it be any good ,having access to test equipment,would you know what to look for . Only saying!
  16. HarDeBloodyHarHar

    HarDeBloodyHarHar Active Member

    My opinion is yes, it might. Change the switch as a test.

    And remember, on a two-way switch, either switch sends the power through both switches.
    Karl Taylor likes this.
  17. Karl Taylor

    Karl Taylor Member

    Probably not to be honest with you
    So think i buy a new switch and then if that fails to fix it i get a electrician in before i buy something else which might not be needed
  18. unphased

    unphased Screwfix Select

    Its probably the lights, as I've already told you. Your wasting your time buying switches, they wont be the cause. Switches are just switches, wires are just wires. The lights contain components that fail, so start there. It is obvious to me anyway, maybe you think your better than me? I'm just an electrician with 15 years experience so just ignore me. A decent electrician would go straight to the two florescent lights causing problems.
    Cecilb70 and Karl Taylor like this.
  19. Karl Taylor

    Karl Taylor Member

    thanks for that information. only thing i carnt understand is why if you flick the switch on either side , ie switch one of the lights off then the other and then the other way round it trips the electrics so giving no indication as to which light is faulty . i would expect it if you switched one light off and it trips it would be that light and same for other light not both?? that what i asking , unless both linked and need test equipment to check both out etc
  20. unphased

    unphased Screwfix Select

    Two way switches are linked. You are trying to separate two linked switches in to separate entities. Forget the switches, concentrate on the light fittings. Disconnect one of them and switch it on and off. Then reconnect it and disconnect the other one, do the same. That should tell you.
    Karl Taylor likes this.

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