"Paul Kierstead" wrote in message
news
In article . net,
"Mike Marlow" wrote:

Well, I understand this, but I would have to wonder why anyone would
wear a
wrist strap when working with the mains. Touch the mains with one hand
and
ground with the other and a resistive ground strap isn't going to help
you
one bit. How much current is any resistor built into a wrist strap
going to
take? How long is that going to afford any protection - if it afforded
any
in the first place? If you wanted a device which provided a better path
to
ground than through your heart, you would want a non-resistive path. A
simple ground braid. The only purpose I know of for a wrist strap is
specifically for static electricity. I can be educated though - am I
missing something?

Ahh... yes, a few things in this particular case, which is OK, we all
have mental blocks sometimes.

Who me???? Mental blocks???? Sometimes????????? You're too kind...


- It isn't about working on the mains, but about accidents that happen.

The post I replied to mentioned mains, that's why I comment on them.

A power supply might be plugged in and wired incorrectly, for example.
The oddest things happen. I remember working on a darkroom timer
(digital) once; it had the grounding plug cut off and was wired with the
neutral to the case. The plug was in upside down and I got quite a jolt
from the *case* (this is why it was being serviced). If I had a
non-resistive wrist strap on, the unpleasant experience could have
become a fatal one.

Correct, but in this case no wrist strap would have been better than a
resistive one. The original symptoms called for checking voltage on the
chassis to ground. This is not really a wrist strap issue.

Rule one of working with power: Accidents happen.

Yes they do and doggoneit how comes it always seems that they never happen
to the other guy?

- The resistor limits current a lot. Lets say your body is zero
resistance; a 5 megaohm resistor will limit current to microamps. It
does'nt have to "take" current; it limits the current simply (consult
ohm's law).

The basic problem here is you should not be attaching anything to your body
in the hope it will conduct current like that. You stay away from making
complete paths to ground from high voltage. Again - in this situation, no
wrist strap is better than a resistive one. Consider - the only way your
resistive wrist strap is going to be beneficial is if you have no other path
to ground through your body. You're insulated at the floor and the only
path to ground is that strap. No strap - no path to ground - no current
flow. Conversely, perhaps you're on a conducting surface and you do somehow
have a path to ground besides through the strap - that's the path current is
going to take - not through the 5Mohm resister.


--

-Mike-