When I'm working on computers, I want to avoid electrostatic discharge. I have a wristband, but I'm not sure that I'm attaching it to the right thing.
ESD rule number 1 - The aim is to have all objects being worked on at the SAME potential.
If this is ground potential, so much the better.
Computer ground and wrist-strap clip should be connected.
Connecting both to ground is a desirable bonus.
The aim is to have you and it at the same voltage.
- Usually, I'll clip it to the case of the computer. However, there are two cases in which I'm not quite sure what the proper procedure is.
As above. The aim is to get you and ALL the electronics that you are working on at the same "potential". This should ideally be ground potential - but it is more important that you and the work be at the dame voltage than that you be at ground. In fact, if you are at ground and the circuit you are working on is not, you MAY do more damage by having the earth strap than by not having it. May.
If there are two cases, ground or connect them both in some way.
- First, sometimes laptops seem to have a all plastic case until you take them apart enough.
They will often have a ground connection or a jack etc that has "grounded" metal. If none of these then see below.
- Second, things like harddrives are ESD sensitive, but when you get them they aren't in any computer, so what should you attach to? That got me to wondering if it would work for it to be attached to a ground (like the third prong in a US outlet, which is attached to a grounding rod or water pipe). Could someone clear up for me what will work to avoid ESD and what will not?
You need an "ESD safe" work area. Typically this is a grounded work surface that is mildly conductive. An ideal material is "butyl rubber" which is used for roofing and waterproofing. This has carbon black included in it which is what makes it conductive.
Price is reasonable compared to almost any alternative. You can sometimes get scrap roll ends or sheet covers used to cover bales which are even cheaper.
Ideally avoid a high conductivity surface such as a metal sheet if you are going to work there with circuits with power on (magic smoke happens) and if you have a PCB with makns or high voltage on even butyl rubber sheet may end up smoking if you apply enough voltage :-(.
A common metal sheet is better than nothing at all - just keep ALL power away from it.
ESD will discharge to ground quit quickly via a 1 megohm resistor. Connecting one og these in the wriststrap gound is wise - unless there is one there already.
To what do I connect the grounding-setup, as a whole? (The mat, or the wrist-strap, or whatever.) I've been told everything from a water-pipe (would have to run a wire to the ceiling, there's nothing down low in the room), to the center-screw of a wall-outlet (really!?) … and, practically-speaking, how do you suggest I do so? Wrap a bare/stripped copper wire around the screw, or around the pipe? Or what?
You want everything Earthed. The center screw of a wall outlet is probably easiest. Make sure you verify that your work area's electrical installation is up to code, and there isn't a ground neutral reversal, for example. Your mat and wrist strap will probably have spade lugs for making the connection.
I know I should be working on an ESD-disappating mat, with an ESD-disappating wrist-strap on at all times. To what do I connect these? Do I connect them together, i.e. to a common point, as well? (From my still-fledging understanding, there should be a single shared ground amongst all points in the circuit, which I suppose includes your body if you touch a conductive part of the board, so …)
Connect them both together, back at Earth.
Is the “ground”, as discussed in terms of dissipating triboelectric
potential / electrostatic charge, the same as the “ground” in circuits
I'm working on? i.e. should I be connecting “ground” in any circuit,
with a wire, to the same grounding-system we're discussing here? Or is
that a separate ground? I've also got a bench power-supply with a
‘ground’ banana-socket, which I'm sure will be used for circuits, so I
suppose … if the answer here is yes, I should wire that to this
common-ground as well?
This is a topic for a separate question all together. Ground has come to be a generic term for circuit common, or zero Volt reference. You may, or may not, be able to make Earth your circuit common, depending on your circuit in question. If your bench power supply is galvanically isolated, it's typically ok to make that connection. More often than not that is through the ground clip on an oscilloscope. For ESD purposes, you don't connect to your circuit. You need to be careful about this, and research it further.
The bench multimeter I've acquired has a grounding screw on the back, next to the three-prong power-plug. Should that grounding-screw also be wired to the common-ground discussed here, i.e. the same as my wrist-strap? (Also, why the hell is there two grounds on that, then; one as a screw, and one as the third prong in the power-cable?)
You can, but for your purposes, it probably won't help much. The safety ground for the chassis is part of the three prong cable. That lug is intended to be connected to a low impedance instrumentation ground. Such a ground will be at approximately the same potential as earth and likely on its own ground rod, but won't won't have all the noise of the building's main electrical safety ground. The safety and instrumentation grounds must be tied together at some point, by code. That is typically as close to the ground rods as possible.
Best Answer
Typically, an ESD-safe workbench is grounded via the wall plug as it's the only decent ground available. It's the same connection used to power the lights, soldering iron etc. via the benches convenience outlets.
When I did this regularly, I found I often had to work in areas that didn't have a suitable grounded bench, so I took a standard ESD strap and mat and wired them to the ground pin of a 3-prong plug. It looked like I was plugging myself into the mains, but the hot and neutral pins didn't go anywhere. Problem solved, works anywhere in North America.
I live in Asia now, where they don't appreciate grounded circuits. At all. Everything is 2-pin, with a short green pigtail on the cord that is useless as there is nothing to attach it to. However, it's humid enough that static discharge is a very minor problem.