Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!tut.cis.ohio-state.edu!cs.utexas.edu!uunet!mcvax!ukc!etive!epistemi!edai!cam
From: cam@edai.ed.ac.uk (Chris Malcolm    cam@uk.ac.ed.edai   031 667 1011 x2550)
Newsgroups: sci.electronics
Subject: Re: Touching a "hot" connector
Message-ID: <444@edai.ed.ac.uk>
Date: 23 Jun 89 20:49:46 GMT
References: <89Jun8.160452edt.10877@ephemeral.ai.toronto.edu> <843@corpane.UUCP>
Reply-To: cam@edai (Chris Malcolm)
Organization: University of Edinburgh, Edinburgh
Lines: 37

In article <843@corpane.UUCP> sparks@corpane.UUCP (John Sparks) writes:

>In article <427@edai.ed.ac.uk> cam@edai (Chris Malcolm) writes:

>/Not recommended unless you don't mind the occasional jolt from the
>/mains, which probably means your skin ought to be on the dry side. I'm
>/talking about 250V mains, by the way. 120 is less lethal.
>               ^^^^!
>Er, not wanting to flame you... but that's stoopid! Why do you want to risk
>your life? That's exactly what you are doing by touching live 250VAC. It only
>takes milliamps to stop a heart. The current is passing from your hand to
>ground (probably your feet), and passing by your heart on the way down. 

I was talking about feeling a faint sensation when touching live mains
with one hand while no other part of the body is grounded. The current
in this case is so trivial that some people can't actually detect it.

As to the heart-stopping bit, since I was told that I've been careful to
keep one hand in my pocket when playing with live mains with the other,
in order to stop the current going through the heart. But, like lots of
other people I know, I have had a few dozen 250V shocks from one hand to
the other, which would seem likely to pass through the heart, and it
didn't stop, or give any evidence of upset. In the days of AC and DC in
the UK some electricians would routinely discover whether a house supply
was AC or DC by sticking their fingers into a live light socket. 

The resistance of the body is largely due to the skin contact points,
and is considerably affected by contact area and dampness. It changes by
orders of magnitude as you pass from light touch to strong grip. Next
time I'm near appropriate equipment I'll measure my ranges of resistance
to these kinds of voltages and tell you, but I suspect the dangers of
_light_ touch with _dry_ skin are much exaggerated - as they should be,
for the sake of general safety.
-- 
Chris Malcolm    cam@uk.ac.ed.edai   031 667 1011 x2550
Department of Artificial Intelligence, Edinburgh University
5 Forrest Hill, Edinburgh, EH1 2QL, UK