That was the problem, Dean! I was too busy holding up... Oh, well... :) But interesting info!

My concern stemmed from having "zapped" my VCR long ago when touching it - with spark - after walking on a carpet. It shut down, and needed an unplugging boot to restart.

Rob
 
----- Original Message ----- 
From: Dean Kukral 
To: [log in to unmask] 
Sent: Saturday, June 20, 2009 2:36 PM
Subject: [PCBUILD] Fw: [PCBUILD] It is neither necessary nor desirable to ground the case to a wall socket - follow-up


Well, it is impossible to say no, but "zapping" might be a bit strong.

This phenomenom is related to that of lightning striking a car.  I have heard that inside a car is one of the safest places to
be during a lightning storm, because you are surrounded by a metallic sphere.  But, if you touch the door handle while it strikes,
might you still be safe or can you get shocked?  That is the question, here.  The answer might depend on several variables, such as
where the lightning strikes, is the car grounded or insulated from ground, and other conductive situations.  You are asking if you
are safer in the car if it is grounded than if it is not grounded.  (For example, your tires are dry.)

Charge will tend to go to the outside of the case, and, from there, drain off at sharp edges.  It is not inconceivable that for an
instant some charge would dristribute itself into the the innards of the computer to those parts that are grounded, such as the 
substrate
of the integrated circuits, if grounded.  [The motherboard likely has a thin copper ground plane (or they used to) which would slow
things up.]  It is only speculation on whether it could do any damage, and, if so, how much.  I am not knowledgeable about static
damage, but my understanding has been that damage comes from zapping a chip, causing immediate burn damage, burning
out the aluminum and other microscopic connectors, and weakening others.

Whether grounding the case would lessen the potential for damage is also speculative.  IF damage is possible, then grounding the
case first might lessen the chances for damage, because the ground would give a low-resistance path to ground for the current
as opposed to the capacitive path into the logic.  Certainly, like the car, the inside configuration and overall construction
of the case would have some effect on the outcome.

Perhaps some research has been done in this area that someone knows about, not just speculation.  It might make a good senior
project for an EE student who has sensitive measuring equipment at his/her disposal.

This can all be prevented by placing a resistor in the wrist strap to prevent "zapping," but you would want the alligator clips
insulated, too, or the purpose of the resistor would be defeated.

I have heard that static damage is most likely to circuit boards when the board is out of the case, so stuff should be kept in the
plastic bags for that reason.  When the boards are plugged in to the case (motherboard, memory, video card, etc.), they are
relatively safe because they are grounded to the case.  Your pose an interesting question because of the immediate impulse of charge
as opposed to the slow introduction of charge.  For example, if you carry the case across the carpet, there is virtually no danger
to the components.  It is the components out of the case that are most vulnerable.  But, that assumes, of course, that  you are not
walking across the carpet and then immediately touching an ic!

Maybe if you wear a belt AND suspenders, you would ground yourself first to something else and then attach yourself to the computer.
:)

Dean Kukral


----- Original Message ----- 
From: Robert Citkowitz
Sent: Saturday, June 20, 2009 11:15


What-if question:

If you connect yourself to the uplugged computer via wrist strap, couldn't you be zapping the computer/chips with whatever static
charge you had built up (eg, the surprising, sparking amount you get during the dry winter after walking on a carpet) on the way to
the computer?

Rob


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