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
Keywords: touch, sensation, live, shock
Message-ID: <427@edai.ed.ac.uk>
Date: 17 Jun 89 06:16:44 GMT
References: <89Jun8.160452edt.10877@ephemeral.ai.toronto.edu> <814@corpane.UUCP>
Reply-To: cam@edai (Chris Malcolm)
Organization: University of Edinburgh, Edinburgh
Lines: 29

In article <89Jun8.160452edt.10877@ephemeral.ai.toronto.edu>
dudek@ai.toronto.edu (Gregory Dudek) writes:
>
>    I noticed long ago that if you (accidentally) touch a live
>conductor, there is an odd sensation reminicent of a rough surface.
>  Does anybody have a good explanation for this phenomenon?
>

I've always presumed it was a very slight shock due to the very slight
leakage from the body, e.g., the way one can light a neon test
screwdriver by tounching one end to live and the other to you. The
current is so slight as to only be perceptible when it is communicated
through a very small contact patch. Hence it can only be detected when
very lightly brushing the surface. That's all just my guess. I've used
the effect for 30 years to detect live mains by touch. It works best on
shiny surfaces, stroked slowly with a very light touch. It is not a
reliable indicator of _connection_ to live mains, however: the feeling
also occurs in metal connected only capacitatively (i.e. by adjacency)
to live metal. It _is_ a reliable indicator of something not being
earthed, however. The buzz (roughness) is the AC frequency.

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.

-- 
Chris Malcolm    cam@uk.ac.ed.edai   031 667 1011 x2550
Department of Artificial Intelligence, Edinburgh University
5 Forrest Hill, Edinburgh, EH1 2QL, UK