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should unswitched live should as live on a neon screwdriver?
(dave L) wrote in
om:
As a matter of interest do people who know more about electrics than
me (that'll be all of you, then) use these neon screwdrivers? I read
a wiring book the other day which was quite sneery about them, without
being specific about why. I accept your comment that I didn't
understand what it was measuring. As they're sold as a
current-detecting device (ie, to show if a components is live and
likely to shock you) I think they're perhaps mis-sold.
Or is that -more likely, esp in my case- mis-bought?
The trouble with neons, and also to some extent digital meters is that
they are fearfully sensitive, and
It's volts wot jolts, but mills wot kills.
Your switched live has travelled close alongside a genuine live inside a
twin and earth all the way from a rose, or junction box.
So 240 v has radiated into it, but only a tiny amount; but enough to
light a neon, which prolly has half a million ohms in series limiting the
current to about half a milliamp, like blackpool front, but not enough
for you to feel.
HTH
mike r
If this wire was connected even very faintly to earth, all these volts
would dribble straight down, but as it is open at bothe ends ( the switch
is off and the bulb which is out - I infer from your last sentence).
But as it isn't quite high voltages may appear, these are completely
harmless, like the static a good old brinylon shirt will generate.
A good oldfashioned meter with a needle is prolly better to work with, or
as Dave said, try a shunt resistor across a DVM.
(sometimes I think they're more trouble than they are worth, it's truee
they will detect a .1 volt change, or check your battery to within about
a microvolt, but they can cause unnecessary alarm and despondency.
mike r
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