Hi

I was changing a light fitting and have run into an unexpected
difficulty. I don't know very much about electricity, but as it seemed
little more complicated than swapping the wires out of the ceiling from
going into piece of plastic into another, I thought I'd be okay.

Before taking off the old fitting I flicked the switch at the fusebox
for the downstairs lighting circuit, which seems to be turning off the
current in the wires (I've touched them and am not dead!).

However while attempting to connect the new fitting the main fuse
tripped, cutting all electricity to the house. I thought this was
just chance so I flipped the fuse back on turning on the electricity
(leaving the lighting circuit switched off). Again after a little bit
of fiddling the main fuse flipped.

I wonder what could cause this - I thought if the fuse controlling the
lighting circuit were switched off then there would be no electricity
in these wires so they shouldn't cause another fuse to flip. I wonder
if anyone has any idea what is going on. I have isolated the wires
with insulating cable and am leaving it well alone until I know why
this is happening!

Thanks!