Avoiding Static electricty

wrote:
On Saturday, May 26, 2012 3:20:26 PM UTC-7, GT wrote:
Leave the PC plugged in and turn off the socket at the wall to cut the
power - the whole case is then earthed and anything touching the case is
also earther. No need for anti-static straps, wrist things or anything
clever.

Wrong. Really wrong and potentially dangerous.

You shouldn't leave the AC cord plugged in because a direct, low impedance
connection between you and earth ground can be dangerous, as evidenced by
people touching defective toasters and faucets at the same time. That's why
anti-static wrist straps have a million ohms between them and their ground clips.

Some electronic assembly factories make workers go through a checkpoint where
they have to plug in their wrist straps, and any that measure more than about
2 megaohms or less than 1 megaohm are rejected.

It doesn't matter if the computer chassis is at earth ground or 20,000 volts higher.
The only thing that matters is for everything to be at the same voltage, and your
recommendation won't eliminate the need to take anti-static precautions.

Earthing is irrelevant, and adds nothing to the problem of ESD.

"everything to be at the same voltage" a.k.a. equipotential, is exactly what's desired.
Agreed.

When three items being assembled, are all brought to the same potential before
touching one another, there is no delta_V and no net current flow when
they touch. Using the 1 megohm resistor (or the high resistance per square of
an ESD bag), is so any discharge actions required, have a relatively long RC time
constant, causing low peak current flow. Current density is part of the damage
phenomenon. Using the 1 megohm resistor, results in the eventual equipotential
condition, and while things are getting there, the current flow is tiny, and
won't "blow a hole" in any semiconductor junctions.

"Earth" is simply another reference point. Sure, you can earth yourself and
earth the chassis, and earth the ESD bag. And by doing so, you're equipotential
(so no net current flow when the items touch). But you can just as easily
"be your own electrical island", and as long as the three items are connected
by the equivalent of an ESD strap (conductor with moderate resistance), you
won't need earth at all. You don't need to "drain" stuff, as much as you need
"all items charged to the same voltage". It doesn't matter what that
voltage happens to be, relative to any other items not within reach in the
room. If there was a Wimhurst machine across the room, charged to 1 million
volts, since you're not going near it, that voltage is irrelevant. Just
as irrelevant as earth would be.

Paul

On 27/05/12 08:20, GT wrote:
wrote in message
...

wrote in message
...

A friend of mine bought a new graphics card for his computer and he also
got a high end power supply , I told him to contact me when possible so
i can go to his place and install the new upgrades
I dont wanna end up messing it up he is low on budget so i would like to
know
whats the best way to discharge static electricty before opening the
case and working in it


I keep part of my arm on the chassis at all times.

That's fine if the chasis is earthed!

Technically it doesn't matter. so long s chassis, your bodt, the card
packaging and the card are at the same voltage, then there will be no
discharge. Hint, how they work on live high voltage lines.

In the last episode of , Paul
said:

"Earth" is simply another reference point. Sure, you can earth yourself and
earth the chassis, and earth the ESD bag. And by doing so, you're equipotential
(so no net current flow when the items touch). But you can just as easily
"be your own electrical island", and as long as the three items are connected
by the equivalent of an ESD strap (conductor with moderate resistance), you
won't need earth at all. You don't need to "drain" stuff, as much as you need
"all items charged to the same voltage". It doesn't matter what that
voltage happens to be, relative to any other items not within reach in the
room. If there was a Wimhurst machine across the room, charged to 1 million
volts, since you're not going near it, that voltage is irrelevant. Just
as irrelevant as earth would be.

The one advantage that "earth" has is that within a particular building,
if it's properly wired, it's roughly equivalent.

This means that if I touch my desk, computer case, storage shelf, etc,
they all have the same reference voltage.

While it's true that I can be my own "electrical island", as soon as I
bump a metal part of my desk I'll be grounded back to earth, while the
components on the non-grounded part of my desk will be in their own
electrical island.

I prefer to ground my desk and keep everything as close to earth's
voltage level just to increase the size of my electrical island.

--
This signature was randomly selected