28 Feb
2000
28 Feb
'00
10:29 a.m.
These comments are clearly made by someone who has experience with this
matter!
Dick
-----Original Message-----
From: Tony Duell <ard(a)p850ug1.demon.co.uk>
To: classiccmp(a)classiccmp.org <classiccmp(a)classiccmp.org>
Date: Monday, February 28, 2000 4:40 PM
Subject: Re: Is ringing voltage dangerous?
>
>
> >RULE 1, unless the voltage is very low it _can_ be dangerous. Low is
hard
> > number be exact about but, over 12-30V
is the watch out zone.
> >RULE 2, All efforts are to be made to avoid crossing the heart or chest
> > as a possible path for safety. One hand in pocket rule is
derived
> > from this.
> >RULE 3, if you not sure, make sure. get a meter and find out if it's
live
> > and how hot hot is.
>
>
> I just want to add a rule - Don't always trust what the meter says. I
took
I believe that when working on live power lines and other circuits
carrying dangerous voltages, you test the meter on a known HV source,
then you test the line, then you test the meter again on said known HV
source. Then, normally, you connect the power line to earth, assuming
it's shown to be dead. And only then do you touch it.
Some HV meters used for this sort of thing have a 'proving unit' (a small
PSU that gives out a few kV at a minimal current, running off batteries)
in the carrying case for these tests.
> 1950 v from an electron multiplier supply because the meter read around
40
volts. There
was a common failure mode of this supply that it would shut
down to 40 v. Instead of walking around to shut it off before
Ouch!. That's not pleasant :-(. Oh, and never trust indicator lamps (they
can burn out), and never trust on/off switches to isolate something. Pull
the mains plug and put it where you can see it (or some idiot will plug
it in again).
I'll add another 'rule'... When you are sure something is not live, brush
it with the back of your finger. If, by some strange chance it _is_ still
live, your finger will be thrown off. Touch it with the front of your
finger and you'll be forced into better contact with it.
-tony