12V Halogens trip RCD

Discussion in 'Electricians' Talk' started by colinm, Nov 1, 2003.

  1. colinm

    colinm New Member


    I've fitted a 5-spot, 35W 12V halogen lighting system to replace existing ceiling light (Screwfix item #16071).

    At seemingly random times, switching it on causes the upstairs lighting RCD to trip instantaneously - none of the lights come on. At all other times, the lights work fine.

    There is no earth terminal on the transformer, and I have already fitted a replacement transformer with no luck.

    I can't see anything else that's wrong - anyone got any ideas? Could the transformer be drawing more current on when switched on than the RCD can cope with? Surely it should work with RCDs??
    Any advice would be much appreciated,
  2. chtechie

    chtechie Member

    I've seen loose connections cause spurious RCD trips.
  3. supersparky

    supersparky New Member

    yea, on some the initail draw can, lights arnt usualy on the rcd...do you not have a split load? of you do , put it on the main switch.

  4. seylectric

    seylectric New Member

    Are you using the "soft-start" electronic transformers; the ones where there is a slight "pause" before the lights come on, i.e. the type where you can use a dimmer switch? This avoids a start-up surge and should solve your problem.

    Good advice above too, check for loose connections, surely the biggest cause of "false" tripping?
  5. colinm

    colinm New Member

    Thanks for the helpful info
    I've checked and double checked all my connections are good - and by replacing the transformer I had to re-wire anyway.

    I was concerned there may be a short somewhere, but removed all the lights (it's one of those track systems where you have two parallel insulated wires and screw the lights onto them) and still had the problem.

    I'm not sure about the dimmer - I think there may be a slight pause upon switch on but I'm not sure. I'll check the instructions and fit a dimmer as that sounds like the best way forward for now.

    Thanks again
  6. seylectric

    seylectric New Member

    Track systems are a pain for this type of fault but if you have ruled that and loose connections out it definately sounds like the transformer is the problem, and a "soft-start" transformer should solve your problem. Fitting a dimmer will not be necessary, and if it is a transformer problem it will not make any difference anyway if the transformer is not replaced with a "soft-start" type.

    Do let me know how you get on, I will help if I can.
  7. supersparky

    supersparky New Member

    or put the lights on the main incomer side if there is one then there will be no problem with the transformers he has got, although soft start will solve it

  8. seylectric

    seylectric New Member

    Good shout super...we've saved the world again! Over and out.
  9. supersparky

    supersparky New Member

  10. Excalibur

    Excalibur New Member

    I had a similar problem in my bathroom fitted with 7 x 50w LV spots. The electrician at my local shop told me to replace the 6anp rcb with a 10 amp because the lights worked fine except if you turned them off and then on again within seconds it would trip the rcb. I am going to do it but waiting untill I have a good sized order for Screwfix although I will check my connections first, in case that is the problem.
  11. ban-all-sheds

    ban-all-sheds New Member



    What's tripping - the RCD or the lighting circuit MCB?
  12. Excalibur

    Excalibur New Member

    In my case 6amp RCB in the main fuse box.
  13. supersparky

    supersparky New Member

    thats a 6 amp mcb that is totaly different thing and reasons for tripping are also likely to be diferrent

  14. Excalibur

    Excalibur New Member

    That is why we pick the brains of experts as yourself. :>)
  15. colinm

    colinm New Member

    Ah...I may have made the same terminology mistake as Excalibur...it's the 6A fuse on my fuse box that's tripping. I always thought that was the RCD. Sorry.

    Shall I do the same by fitting a 10A?

    I don't intend to replace the transformer - not when I paid nearly £80 for the light! If Screwfix can't supply products that work, then it'll have to go back! :)

    The instructions do say that I can use a dimmer, but not when PLCE lamps are used. Anyone know what PLCE lamps are?? Is it worth me still going down this route?

    Unlike Excalibur, mine trips when switching on, and doesn't necessarily happen if it's just been turned off and back on again.
  16. supersparky

    supersparky New Member

    you could try 10 amp but only if your lighting circuit is run in 1.5mm2 you cant without upgrading if its only 1.00mm2
    And have you tryed switching the lights on with all the other lights in the house off?

  17. seylectric

    seylectric New Member

    I beg to differ, super... 1.0mm2 is perfectly acceptable if the total load on the circuit is not more than 2400 watts - equivalent to 40 x 60w lamps! Voltage drop over a long cable run would obviously reduce this figure but in your average 3-bed semi that would not apply.

    What baffles me slightly here is that there is a surge current present on start-up, but not enough to knock off a 6A MCB in my experience. I still think that the best solution is to change the transformer. Personally I use a seperate tansformer for every 12v 50w halogen lamp fitting, they only cost about a fiver apiece and if one goes down only one light doesn't work instead of a whole series of lamps going down. I'm not keen on these "kits" personally. OK fitting an individual transforme for each lamp involves a little more work, and puts the price up somewhat, but it gets rid of problems like this. Trust me, I've been there...
  18. ban-all-sheds

    ban-all-sheds New Member

    Not necessarily - 1mm cable at 10A gets you 21m. For upstairs lights you could well use 1/3 of that just getting to the loft. Then a meandering path to 3 bedrooms, bathroom, toilet and landing could quite easily exceed 14m.
  19. supersparky

    supersparky New Member

    well im not to keen on the kits either but the only time i will use 1.00mm if for switch drops forthe difference(bout£4) you might aswell use 1.5 then you have no worries about V.D

  20. colinm

    colinm New Member

    Hmmm...sounds like these kits are more trouble than they're worth!

    I think I'll return the product and fit individual downlights with separate transformers.

    I don't know anything about how the house has been wired so length of upstairs circuit cable is totally unknown. Fitting a 10A fuse may just buy me more problems.

    Thanks to all for your excellent assistance!

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