Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!bbn!mit-eddie!mit-amt!mit-caf!ankleand
From: ankleand@mit-caf.MIT.EDU (Andrew Karanicolas)
Newsgroups: sci.electronics
Subject: Re: Touching a "hot" connector
Keywords: touch, sensation, live, shock
Message-ID: <2968@mit-caf.MIT.EDU>
Date: 5 Aug 89 23:29:28 GMT
References: <89Jun8.160452edt.10877@ephemeral.ai.toronto.edu> <814@corpane.UUCP> <427@edai.ed.ac.uk> <1528@sunset.MATH.UCLA.EDU> <498@edai.ed.ac.uk>
Reply-To: ankleand@mit-caf.UUCP (Andrew Karanicolas)
Organization: Microsystems Technology Laboratories, MIT
Lines: 29

>Well, as I promised, I tested my resistance. As I said I have dry skin.
>With a light touch. such as I use for testing mains, my resistance is
>>10MOhm. If I dampen my fingers by breathing on them, and grab the test
>prods painfully firmly, I can bring it down to around 10KOhm. That's
>still an order of magnitude under the lethal current. So you all kind
>folks can stop worrying about me! As a matter of fact, the kind of jolts

You are placing yourself at immense risk.  You are making several 
DEAD WRONG ASSUMPTIONS.  You measured your resistance but thats only
part of the story.  You really need to measure the IMPEDANCE of your
body at the frequency of interest (50 to 60Hz).  You will find that this
impedance is quite different from DC measurement you made.  I recall being
told that 60Hz just about minimizes the impedance of the body. The
other seriously wrong assumption you are making also concerns itself with
the order of magnitude of the impedance: you measured the resistance between
your finger tips.  While using your fingertips to sense mains voltage, you
may expose another part of your body to ground, say the side of your arm, 
or hand, without knowing it.  The larger surface will result in a drastically
lower impedance than you are ever going to get by pinching two probe tips 
until your fingers are blue.  If your skin is moist, say from the humidity
of the air, then the impedance of your body will be even lower.

If I were you, I would discontinue this practice and invest in a neon bulb
tester.  The AC mains are something you should respect, there are many 
needless deaths because of careless procedures.

Andy Karanicolas
MIT Microsystems Laboratory
ankleand@caf.mit.edu