"John Stumbles" wrote in message
...
Lurch wrote:
On Mon, 03 Jan 2005 15:07:12 GMT, "BigWallop"
strung together this:


I've just been reminded of a good story I'd like to share with you all.

The screw driver was presented to the live mains electricity for the
first
time with its new neon lamp installed and................BLAM !!!! The
cruel owner was flung off the top of the step ladder on to his back.
The
screw driver had got its revenge on its cruel owner at last.

The moral of the story is "Make sure you understand how things work,
before
you go trying to repair them".


Excellent!
Another moral is, "if you've bought some useless piece of crap that
was unreliable in the first place, don't bother repairing it".

I've been using neon screwdrivers for decades and find them very useful.
I'm rarely without one: mostly I use it for mechanical purposes (driving
slot-head and small cross-head screws and other less screwdriverey
purposes) but because I have it to hand it's my first-line mains tester.
I find it gives a reliable indication as long as you know that you have
to be touching the contact on the end for it to light up. I'm aware that
it may give false positives (e.g. lighting up on an unterminated
conductor from capacitive coupling from nearby live conductors) and
could give false negatives (the tester may have failed). For the latter
reason I make sure it lights up on a known live terminal before putting
too much trust in the absence of a indication on the cct under test. The
same (false +ves and false -ves) applies to high-impedance digital
multimeters, and any indicator will give false negatives if broken.

The moral, to extend on the OP's, is to understand how things work
before putting trust in them.

And what better for sticking into the terminals of a central heating wiring
box than a neon screwdriver. A multimeter needs two steadily held terminals
and usually a head turned 180 deg as shown by the girl on the exorcist to
see any clues as to the fault. A volt stick lights up as soon as you enter
the wiring box and is so unhelpful.

Neon testers do have a useful but limited purpose in life.

Adam