MCB trips when light is switched off?

You have probably miswired the new light fitting - you have very likely connected switched live (looks like a neutral) to neutral - and permanent live to the new light.

When the switch is OFF the light comes on and all looks well - when you set the switch to ON a direct connection is made between Live (the neutral looking wire that's not a neutral) and neutral; with no light as a load - the fuse breaker will complain.

Look at your light switch - you will probably see two wires of different colours - BOTH of them are Live, one of them turns the light on and off.

Peccavi
October 2009

thanks ill check that out

eric wilson
October 2009

It could be in the switch itself...but also a connection from a neutral to earth would cause this. Check out your work again!

John
October 2009

i wired from the house to the shed put an MCB and Two RCD one for lights one fore a socket the socket is fine but the lights as i said where would a loose wire be likely to be?

Eric Wilson
October 2009

The switch is sparking internally - try a different one after making sure that the cable terminal screws are tight.

John
October 2009