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The MCB gets tripped when ***** is switched on, how do I establish which of the light wiring connection is shorting.
What you describe is a very serious direct short. Did you mean one of the 15 or 20A breakers trip?
I assume you've unplugged all the receptacle loads and turned off all the lights and the problem still exists.
If so, I like to lift the wire to the tripping breaker and one lead of a 100W light bulb to the breaker. Connect the other lead from the light to the wire you removed from the breaker.
Now, turn the breaker back on. If it lights to full brilliance you still have a short on the circuit.
Turn off the breaker and go to all the receptacles that are off and remove one of them from it's box. Look for soot or traces of arching. If no problem is seen, disconnect all the black and red wires, but mark how they were connected.
If the bulb is dim or out when you turn the breaker back on the problem is further "down line" and you disconnected the problem from the breaker.
Pick another box that is out (in another room) and repete the same procedure as above.
I've used that procedure for over 40 years and just learned it's called the "binary" troubleshooting method by some. I suppose because by picking a box halfway in the circuit you eliminated a lot of boxed quickly. Good luck!