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I have a lighting circuit in my home like so:

Circuit

Every time I turn on the switch, the breaker trips. This circuit has existed for over four years and only now has the problem begun.

I've checked all connections (neutral in the switch was burnt from the original, probably caused the original trip) and they are all fine. In the moment before tripping, all bulbs are lit.

Any ideas what is wrong and what is the remedy? I'm hoping for options that don't require a rewire as that would mean a re-plaster. :(

Note:

  • There are actually ten bulbs in the circuit, but I drawn only three for brevity.
  • The bulbs are actually 50W GU10 down lighters.

what I've tried so far:

  • Removed all but one bulb from the circuit
  • Replaced the bulb
  • Tested the bulb in another circuit proving it works
  • Removed the bulb
  • Replaced the switch with a proved to be working one
  • Removed the switch
  • Moved the switch to the neutral wire
  • Changed the RCB

All of these result in the same outcome. The breaker always trips.

Update
The following diagram demonstrates how the physical wiring runs:

enter image description here

  • Are they individual fixtures or part of a track light system? – mikes Mar 14 '15 at 18:32
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    Remove all bulbs. Does it trip when turned on? If not, put in one bulb - same question. Move one bulb from fixture to fixture - same question. Something has become faulty, it's a matter of tracking down what. – Ecnerwal Mar 14 '15 at 18:51
  • @mikes They are individual fixtures. Just standard down lights, a standard on/off wall switch, and a 6A RCB. – Paul Fleming Mar 14 '15 at 18:53
  • @Ecnerwal See my update for everything I've tried so far. – Paul Fleming Mar 14 '15 at 18:54
  • Your update could be clearer, in the sense of "...and in every case the breaker trips when the switch is turned on." ...which you didn't quite say. If that is the case, (ie, it trips with no bulbs in circuit, with a new /different breaker, etc, etc.) then you have a wiring fault and I suggest you get in a replastering mood, because it's "the gasman cometh" time for you. – Ecnerwal Mar 14 '15 at 18:58
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I know you are to avoid making statement based on opinion, so here is my thought.

The Breaker, like me, has gone soft and infirm.

The 'thermal' part of the thermal-magnetic breaker was willing to tolerate the slow death of the burned switch, but it weakened itself in the process. So the slightest load will now trip it.

  • I'm not sure I understand your answer. I tried it on a different breaker with the same problem. I also tried a different switch. The only thing (other than the wiring) that I have been unable to change is the actual first light fixture. I disconnected the rest from the circuit. – Paul Fleming Mar 15 '15 at 21:56
  • Forgive me, please - I was thrown by RCB – Some Guy Mar 15 '15 at 22:54
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The simple answer is the one you least want to hear, though most likely the correct one. There's a fault in the wiring, and the breaker is doing the job it was designed to do.

If you don't have the tools and/or knowledge to locate and repair the fault, it's time to step aside and let the pros do their thing.

  • Thanks for the honesty. What tools are you referring too? – Paul Fleming Mar 15 '15 at 21:53
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If none of the above is fixing the issue... it will most likely be inrush current. Drivers for LED lights have a very high instantaneous inrush current at start up. A 6a RCBO will not cope well as it it a very low amperage. Try take half out and see what happens

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What type of breaker do you have? I have experienced a similar issue with circuits protected by GFCI breakers. It could be bad wiring or it could be a light fixture that has a short of some type or it could just be the GFCI breaker. Id try everything prior to rewiring!

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