Bulb blowing on new 3 bulb light?

Hi
I bought a new 3 bulb (E14 type) ceiling light. When I turn on the wall light switch it blows the bulb. It's alway's the same socket. If I screw the bulb in when the light is already switched on it doen't blow. I had to use choc blocks when fitting as the wiring coming out of the celing cables would not fit into the one's on the light. I did not use insulation tape to cover the blocks so could this be the problem? Any other ideas? Thanks.