On 10/12/2017 22:55, D.M. Procida wrote:
I noticed that the wire into a ceiling lamp lit up an electrical
screwdriver when I checked its terminal, and it did the same at the
switch end - even when I completely disconnected it from both ends.

I'm pretty sure that this was a single uninterrupted wire from switch to
lamp, with nothing else connected to it, but I can't be 100% certain.

I assume that there was a very low induced current in the wire from some
other nearby wire; whatever it was, I couldn't actually feel anything
myself when I touched it.

Is this normal behaviour for an electrical screwdriver, to be so
sensitive?

Daniele

Assuming you mean a *neon* screwdriver, yes it is not uncommon, although
with experience you can usually differentiate between a "true" and a
"false" live, the latter lights the neon more faintly and sometimes
there is some flickering.

A useful tool in sufficiently skilled hands. The "volt stick" is also
very useful in diagnosis since it will sense live through insulation,
but some also seem to show false positives, and others can be a bit low
on sensitivity.