Light switch regularly blowing main fuse

[rfarrand@madasafish.com]

I have recently moved house and replaced all the light switches. One is a problem , it is a 2way switch , in the lounge , I have replaced the other switch that also controls the same light but its never used. The problem switch seems to me to be very strange. It regularly blows the main fuse but when its being swithced off, never when its being switched on. Sometimes it last weeks , sometimes just a couple of days. Any help much appreciated

[sparx]

Hi, as no neutral at sw. the only way to blow a fuse with a sw. fault would be Live to earth contact, most likely way is you have a wire in behind lug of sw. box and sw. face plate mounting screw is too long & bearing against wire, remove sw. & look for tell-tale mark on wires.
regards SPARX

[sparks]

sorry about name sparx had no idea it would be so close ,hi respect for the advice you give ,regards sparks

[rfarrand@madasafish.com]

Hi Sparx, thanks for advice but have checked both switches out and there seems to be no wiring problem. I have experimented and find I can blow either of the 2 switches (which are about 20 ft apart) and when they are not screwed to the wall. I find it strange they only blow on switchinf off the light ??

[sparx]

Hi agn, yes very strange... unless there is an earth fault on one wire of 2 way which is only Live in certain sw. combination which coincides with light being turned off ie one of the 'strappers' between L1's OR L2's, will need insulation tester to verify which ain't the sort of thing a non-leckie would normally have!
sorry but I think it's that time£££
regards SPARX

[rfarrand@madasafish.com]

Hi Sparx, thanks for latest comments, I think you are right I need to spend some £££

regards
bob