Path: utzoo!utgpu!jarvis.csri.toronto.edu!rutgers!usc!csun!psivax!torkil
From: torkil@psivax.UUCP (Torkil Hammer)
Newsgroups: sci.electronics
Subject: Re: Touching a "hot" connector
Message-ID: <2793@psivax.UUCP>
Date: 26 Jun 89 17:43:54 GMT
References: <89Jun8.160452edt.10877@ephemeral.ai.toronto.edu> <843@corpane.UUCP> <444@edai.ed.ac.uk>
Reply-To: torkil@psivax.UUCP (Torkil Hammer)
Organization: Pacesetter Systems Inc., Sylmar, CA
Lines: 47

You are discussing 3 different things.

One is an electrical shock, as you can get from touching a live 110 or 220
V wire.  Usually those shocks are not lethal, but if you stand on a wet
grounded concrete floor and/or get them through the heart they can be.

The second (original posting) is a capacitative coupling between
equipment (lamps, stereos, appliances) and you.  The coupled voltage
can be high - up to the line voltage and possibly higher, but the generator
impedance is several megaohms, so the fuzzes don't harm you.
The fuzzes can be induced by microamps, but not everybody can feel them.
I experienced the fuzz the first time from a well insulated lamp on a
wooden table.  It went away when I reversed the plug, but much to my
surprise the proper position of the plug depended on the position of the
lamp on the table.  Which goes to prove that the effect is not ohmic
conductive, but must be of proximity coupling nature.
The fuzzes are difficult to reproduce, because you need just the right
skin resistance to make them work.  You also need the right muscle
tension.  I think they work by having a small current trigger muscles
nerves that are already biased.

The third is the jolts you get from cattle fences.  These are kilovolts
delivered through an impedance high enough to make it safe in most
situations.  Because the source impedance is very high, the fence delivers
a current that does not depend on how well you are grounded - the jolt is
the same whether you stand on dry or wet soil, though if you grip the
fence you can get your skin resistance so low that you barely feel
the jolt - the most of the current bypasses along the surface of your skin.
Warning:  Don't pee on an electric fence.  The shock passes directly
through rather sensitive body parts.  The jolt can knock you unconscious
and possibly do some internal damage.

Finally, don't play with neon bulbs without limiting resistors.
The bulb is started with a peak voltage of 90-165 volts or so,
but then enters a negative impedance region where an applied
voltage of low impedance can make the thing explode with sparks
of white-hot bits of metal coming out through the soldered end.
These sparks can burn holes in carpets, hands, eyes and whatever
else gets in the way.  A limiting resistor of 220 kohms is
standard for 110-220 VAC applications.

If you want to check the house wiring, you can (at least in USA)
buy a 3-pronged gadget that contains 4 neon bulbs arraigned in
a pattern that can detect most miswirings including reversed and
disconnected wires.

torkil