Mike Marlow wrote:


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

The point being - you do not
need a resistor in series to safely discharge static electricity.

I think you misunderstand the purpose of the resistor; AFAIK it is not
to safely discharge *static* electricity, it is to prevent you from much
higher chance of death in the event of electrocution, for example if you
should touch the mains. One of the most dangerous scenarios is when one
hand touches the mains and the other is grounded; this puts the current
directly across the heart. Wearing a wrist strap is just begging for
trouble in the event of an accident. A resistor mitigates this risk.

PK

Well, I understand this, but I would have to wonder why anyone would wear
a
wrist strap when working with the mains.

One doesn't. But power has a way of appearing unexpectedly on the bench.

Touch the mains with one hand
and ground with the other and a resistive ground strap isn't going to help
you
one bit.

Touch the mains with one hand while wearing a NON-resistive ground strap on
the other and then what?

How much current is any resistor built into a wrist strap going
to
take?

Well, typically the resistor is 1 megohm 1/4 watt, which should be within
its power rating up to 500 volts, at which point the current through it
would be 500 microamps.

How long is that going to afford any protection - if it afforded
any
in the first place?

Unless you're working with more than 500 volts it should provide protection
indefinitely. And when it fails it tends to fail open and break the
circuit rather than fail short.

If you wanted a device which provided a better path
to
ground than through your heart, you would want a non-resistive path.

That is not the purpose of the device.

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?

Yes, you are. The purpose is to eliminate static. The use of the wrist
strap, however, introduces a new danger--a path to ground through the wrist
strap. The resistor is there to eliminate that specific danger by limiting
the amount of current than can flow through that path to a level that is
not dangerous.

--
--John
Reply to jclarke at ae tee tee global dot net
(was jclarke at eye bee em dot net)