Corran wrote:You don't seem to understand what I'm saying. The only thing that has to be the same charge is yourself and your computer.
ESD sensitive devices can be potentially damaged it they suddenly meet a charge different than what they already are. When you touch your case or attach an ESD wrist strap, you drain or add a charge to the ESD sensitive device in a non-destructive way.
Touching your plumbing before touching you computer will only increase the difference in charge between yourself and the computer. So not only does it not help but it potentially worsens the situation.
You're both right and wrong about different things. Suppose you're working on your PC, then leave for a bit, then walk back to it over a dry carpet. Suppose you touch the PC frame and a spark jumps from you to the metal. That charge is going to go someplace: into the case metal, the power supply box, through the ground wires to the motherboard and anything else connected to it. Theoretically, you can damage your PC just by discharging yourself like they tell you to do - although in practice I have never seen this happen.
Ideally, the PC would be sitting on an antistatic mat that is attached to an "acceptable" ground. You would then attach yourself to the same ground using an "acceptable" strap.
Then you can touch the computer. In other words, you reach the same state of charge using something other than the device you're trying to fix. This is what we're taught in our certification classes at work.
As for "acceptable" grounds: Sink pipes as grounds are an old method based on the fact that the best ground around is literally ground; i.e. dirt, like that in your back yard or under your house. The wetter it is, the better. Most water piping reaches the dirt somehow or other, but it has to be metal pipe. Most homes use plastic PVC pipes for drains, so the cold water supply pipe is a better choice. In some homes, you can find a large metal stake driven into the dirt near where the power lines enter the house. This stake will have a wire or cable connecting it to the home's electrical lines.
In the labs where I work, we use 1 inch by 1/2-inch thick copper bars typically 10-15 feet long. They're connected to the building's electrical ground. Here at home, I have two antistatic mats and I've connected them to the metal frame of my desk.
By "acceptable" wrist strap, I mean something with a resistor built into it. When you grab a wire or touch the case, you make yourself the freeway for any current going to the ground. Read that as potential electrocution. A good wrist strap has a large enough resistor to keep the current to a survivable level. This is just a last-ditch safety measure. You should not be touching any power sources to begin with.
As Corran suggests, putting on a good wrist strap first, then connecting its wire to the case, should be safe enough in practice. The resistor in the strap should prevent a sudden current flow into the case.
Despite all the training I've had to take on this subject, I still build my own PCs with everything spread out on the carpet. Haven't roasted anything yet although I do try to keep some part of me (like toes, if necessary) in contact with the case when I'm working inside it.