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

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?

Yup. I've got one of those table lamps which turn on when you touch the
metalwork, and that lights a neon screwdriver dimly, showing that they
put mains (or near mains) voltage through you. Real electricians dislike
them as they respond to leakage currents.

--
Max Demian

On Sunday, 10 December 2017 22:55:33 UTC, 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

Yes it is. It's voltage produced by stray capacitance, not inductance.


NT

Yes.
They are and can only be a rough guide. My old Neon one when I could see
could light up if you just laid a wire alongside where a mains cable went. I
imagine the newer kind use some kind of fet and an led to do the same job,
but either way, I'd not want to trust on myself.
The only use I ever found for them was as a confidence check that an
appliance was absolutely dead and disconnected. Anything involving runs of
wire will be very ambiguous.
Brian

--
----- -
This newsgroup posting comes to you directly from...
The Sofa of Brian Gaff...

Blind user, so no pictures please!
"D.M. Procida" wrote in
message
...
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

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.

On 10/12/17 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


Depends on the 'electric screwdriver'- they are not the most 'reliable'
or safe items. As you surmise, they can detect 'stray' fields / currents
and give misleading results.