Electrical – Lighting circuit trips breaker every time

circuit breakerelectricallighting

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

Best Answer

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.

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