A neon will glow with very small amounts of current.
You can wave one near any radio source and its quite likley to light up.
I suspect you simply were seeing capacitive pickup from somewhere - maybe other mains, maybe local transmitters.
IIRC you are right. It is practice to throw a an earthed chain over teh cables to be worked on I think.
if you`re working on switchgear, you will have the "hot" stuff usually hidden away behind an interlocked cover with ceramic or shellac`d paper bushings - these bushings are referred to as spouts.
So for a HV circuit breaker, you will normally have six spouts (two per phase) - one on the busbar side and one on the "outgoing" side
Hello Jon
Sorry for late reply, behind again.
Might be an obvious question - but does the screwdriver have an internal battery? (Usually a button type inside the transparent handle).
If so, it's one of those annoying and potentially dangerous "all in one" things that do continuity as well as testing for mains.
I don't recommend 'em for just this problem of false positives.
I have seen this on lighting circuits which include a florescent fitting.
Even when the circuit was isolated from the mains the tester indicated a current present.
More a voltage, really. The current required to light a neon is so small in domestic terms as to be insignificant. That's why they're near useless.
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