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[ched2be]

i m installing ceiling light the light works when the switch is off but when i turn the switch on it trips the main trip switch

[sparx]

hi, you have put all lives together & all neutrals together, right?
WRONG! see DOC's project section for wiring a light.
If old wiring is red/blk, then one of the blks would have been on its own in to Live of light as returning sw. live, other blks would have connected to Neutral of light , reds did not connect to light at all & would have been in seperate connector block looping to each other only
By putting sw-L. in with N when turning sw on will Cause a 'short-circuit' & trip MCB.

[jackhawk]

ched2be,
You have connected all like wires together. This will allow the light to work with the switch off but when you swith on at the wall you are causing a short circuit thus tripping mcb. Switch off mcb for light circuit and ID the switch wires. Depending on age of wires you will have red/browns(L) and black/blues(N) at the fitting. You need to ID the switch wires. The black /blue switch wire return needs to be sleeved brown. All the Brown/reds need to be connected together with a 10A block including the switch brown/red. The blue/black switch return wire (sleeved brown) will go into the light live. All the blues/blacks need to be connected together in a block with a blue wire connecting the block to the light N. I assume the fan light is metal so ensure all earths are sleeved green and yellow and terminated in the LIGHT earth block. Good luck with the arm ache.