On 10 May, 20:30, Drake wrote:
I was mystified by something I experienced today. I'm sure any
electrician will know the answer. Sorry if its a naive question.

I was using one of those electrical screwdrivers with abuilt-in diode
for identifying live wires. I wanted to disconnect a security light on
my house but I wasn't sure which circuit it was connected to. I
concluded the light was wired into the lighting circuit, because it
failed to come on after I pulled the main fuse from that circuit. But
just to play safe, I touched the screwdriver onto the terminals in the
junction box which the light was connected to. The diode didn't light
up. However, when I touched the brass end of the screwdriver's handle,
it lit up, quite brightly. So I found my volt meter and tested the
wires to see if there was any voltage there. No voltage registered.
Can anyone explain why the diode lit up when I touched the brass end?
And it lit up the same, whether I touched the screwdriver onto the
live, the neutral or the earth terminal.

Regards,

Drake

Did you read the instructions? The light will only light when you
touch the end as you're completing the circuit. Why it lights on all
three wires is somehting else though!