"John Rumm" wrote in message
...
ger wrote:

So, I pulled back the wall switches and did some simple probing with a
neon tester.

Poxy dangerous things! (as you have discovered)

Some wires showed a bright neon - obviously live.

Not always...

Some showed no light - not live.

Not always...

BUT SOME WIRES SHOWED A DULL NEON LIGHT - when other switches were turned
on these became bright.

Not uncommon...

So, my question please. If a neon tester just glows a bit, can this be
due to seeing a neutral with a long run back

It can be seeing a unconnected wire that is running a distance close to a
live wire and is hence capacitively coupled to it.

Two way lighting circuits are exactly the sort of place you tend to find
this and hence these things are no use to man nor beast in fault finding.
Even a digital volt meter can give you spurious results. An old analogue
one will tend to be more accurate since it will normally place enough load
on the line to dicharge the (tiny) capacitance.

to the local supply trafo and hence with some small voltage drop?
Can a neon tester (the screwdriver handle type) register a few volts on
the neutral?

Unlikely to be enough voltage on a neutral to light it. You are correct
that a neutral can and should be treated as a live - in that it can be
held several volts above ground and with a reasonably low impedance - so
significant current can flow from say neutral to earth in some
circumstances.

Or am I losing it totally? Missing some point?

Only that neon screwdrivers are the work of santa!

Any advice (be gentle, please) appreciated.

Dig out a circus diagram for a two way lighting circuit (there are a few
ways of doing it - my favourite wires the live and swtich return across L1
and L2 on the nearest switch and then simply joins L1, L2, and COM, to the
other switch using some three core and earth). Work through it methodicaly
with a clunky old multimeter (in fact a digitial will often work in that
you can usually see the difference between real 240V live and a coupled
but floating wire)

P.S. Plan B is to switch off the supply to the house, isolate all the
wires from the switches and use a meter to trace the wiring.

That might work as well. ;-)

--
Cheers,

John.

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Many thanks to all who replied. Problem now fully understood.
Neon testers now reduced to the role of screwdriver - intestines removed.

Ger - a happy camper!