Path: utzoo!mnetor!uunet!mcvax!unido!ecrcvax!ralph
From: ralph@ecrcvax.UUCP (Ralph Hill)
Newsgroups: sci.electronics
Subject: Re: Automobile shock hazard (was: shock box)
Message-ID: <520@ecrcvax.UUCP>
Date: 23 Mar 88 07:41:59 GMT
References: <560001@hpcljws.HP.COM> <334@eos.UUCP> <5773@watdragon.waterloo.edu> <888@stracs.cs.strath.ac.uk>
Organization: ECRC, Munich 81, West Germany
Lines: 43
Summary: Automobile electical hazards.

In article <888@stracs.cs.strath.ac.uk>, al@cs.strath.ac.uk (Alan Lorimer) writes:
> The 12V supply in a car is quite capable of delivering currents of the
> order of several hundred Amps. Ok, so what can happen? Well I heard
> of an accident happening to someone a few years ago, whereby the
> bracelet of his watch became welded accross the starter motor
> terminals. 
> 
...burns, etc..
> 
> I would agree that 12V is safe from the dangers of electric shock,
> but please be aware of the dangers of low impedance sources, and take
> care to remove any jewelry before starting work.
> 
> UUCP: ...!seismo!mcvax!ukc!strath-cs!al    DARPA: al%cs.strath.ac.uk@ucl-cs
> 					   JANET: al@uk.ac.strath.cs

Watch the long tools too!  You can easily damage tools or parts of the
engine.  The way to do this is to bring one end of the tool in contact with
some part of the engine, and the other to the + terminal of the battery, or
the heavy wire going to the starting motor (as was the case for the watch
above).  The way you avoid it, is to disconnect the - terminal of the
battery.  Having learned, I now disconnect the - terminal, and put an
insulating cover over the terminal, before beginning any non-trivial
under-hood work.

My lesson:  I managed to stretch a long feeler gauge from the + terminal
to the cam shaft while setting the valve lash.  Fortunately the cam shaft
was a much better conductor than the feeler gauge, and there was good
contact between the feeler gauge and the cam shaft and the cam shaft to its
bearings, ... (i.e., no hot spots).  The cam shaft, cam follower and
bearings all lived.  The feeler gauge made and exciting N-amp fuse!
I consider my self very lucky.  I spent a long time checking for bits of
feeler gauge welded to the cam face, and had bad dreams of welding bits of
tools to all sorts of things.

The feeler gauge was borrowed.  Fortunately the owner was glad to learn the
lesson without risking his engine and thought it was a feeler gauge well
spent.

 ralph hill

P.S. the third party repair manual for my current car begins most
under-hood repair sequences with "disconnect the battery negative terminal"