# Connect anti-static wrist strap to earth wire?

I have started doing some hobby electronics at home and got myself an anti-static srtist strap recently.

I am unsure as to where to attach it to. Most topics I found online regarded PC building and attaching it to the PC case, but I want to use it while handling other things as well, mostly I am scared of killing my raspberry Pi. Since I live in Europe, one idea I had was to attach the clip to the earth connector on a Schuko (3-prong) outlet. But I'm not sure if it would be on the same potential as my pi or other things. And what happens if that clip comes off?

So is it safe to attach it to the ground wire? If not, where else can I ground myself?

• The PE (protective earth) pin of a Schuko (three-prong) outlet would be exactly right. The issue is: how. Many such straps come with an alligator clip. The potential of your Pi does not have to match yours, although it might be wise to 'protective-earth' your Pi too (e.g. via a shielded Ethernet cable). – sekdiy Jun 3 '16 at 21:46
• A plug with only the ground connected (to a bare or GREEN color insulated wire) is more robust than a clip which can come loose. Usual practice is to have a slightly-conductive table-covering pad as well as a wrist strap, both grounded. – Whit3rd Jun 3 '16 at 23:03

There are several considerations for your wrist strap.

A) Safety for you
B) Safety for your fragile components and kit
C) Process, use them correctly
D) Grounded?

Your wrist strap should include a large amount of current limiting before connecting to a real earth. In practice, this is a 1meg resistor in the strap, and/or where you clip it to, and/or a connector that you plug into an earthed outlet to contact the ground pin.

There is no point grounding yourself, if the stuff you're working on can float to any potential. Use a conductive sheet, and place all your tools, components, work in progress, on it, and ground the sheet (via a safety resistor) as well. Metal foil, sheet or a tray will do. In industry they tend to use conductive plastic, which is nicer to work on.

C) Process

Having the right equipment doesn't help if you don't use it correctly. When your PI arrived through the post, it was (obviously) not connected to your grounded sheet. At some point, you have to connect them, and it's at that point a damaging charge transfer could occur.

When you connect them, make sure the point that connects first is a grounded point of the PI, a connector shell for instance. Before you unwrap a component from its conductive bag, or pull it from the conductive foam, touch the bag or foam to bring it to the same potential as you (ground).

D) Grounding?

Once you, you tools, your components, your work in progress are all at the same potential, it doesn't matter whether the whole equipotential group is actually connected to ground or not. In practice, it's a whole lot easier to keep track if it is, and as soon as you use a grounded soldering iron, 'scope or power supply you have that earth connection, so you may as well start off with it.

Your anti-static wrist strap should include a built-in resistor in the order of 1MOhm. If the resistor is present, it is safe to connect the wrist wrap to earth.

If not it is dangerous, because any voltage present in the equipment you are working with would easily discharge through you and the wrist-wrap.

The idea is specifically to bring yourself to the same electrical potential as the ground point of the device that you're operating on. If you've got a way to secure the ground of the Pi to your wrist strap, do that; otherwise you can make a quick-and-dirty ESD mat by putting a piece of thin cardboard or cotton sheet over a sheet of aluminum foil. You can also ground to a metal pipe or any other large metal object, but I wouldn't connect to your home's electrical ground -- you can get shocked that way if there is any defect in your home's wiring

I have always thought the workbench should have a single earth ground attachment point, with the mat, power supplies, electronics and wrist-strap all connected to that one point.

Most wrist-straps include a bleeder resister so you won't get zapped too hard if you touch anything hot. That protects both you and the circuitry.

Whether you connect the wrist strap to the mat or back to the central ground isn't that much of an issue.

The only real concern I've had in the past is when I've use wrist straps that have an alligator clip to connect to ground. If that clip comes off that whatever it is connected to (you, in this case) does not have a reliable ground.

So in my later years I first started hard-wiring everything. Which is good.

But the lazy part of me doesn't want a wrist strip on at all, so I figure simply touching the mat is usually enough to discharge any static I have in my body.

My soldering iron is plugged into the same ground source, as are the workbench power supplies.

One fallacy I think people need to dispel of involves working inside PCs. All the manuals tell you to first unplug it. I humbly suggest this is not a good idea, because if you leave it plugged in the entire chassis is at ground potential, so resting your hands on the metal discharges you enough that it is safe to install RAM and such. It has always worked for me.

When I work on very high-voltage circuitry (like broadcast transmitters), I always follow the left-hand rule: Keep your left hand behind your back. That way any accidental discharge will most likely just go through a hand or maybe an arm, but not through your heart. Same concept as a wrist-strap without having a wire hanging from your arm.

• All the manuals are right to tell you to unplug the PC. Unplug the PC, and touch the PC housing to equalize your potential to the PC before working on the innards. Or unplug and attach your grounding wrist band to the PC. DO NOT monkey around in there with the power on without a damned good reason. – JRE Feb 3 '17 at 8:56
• 100% agree that no power should be on. It wouldn't do to plug in RAM with the power switch on. And yes, if you are going to open up a power supply it should be completely removed and unplugged. But losing earth ground is more important to me than being afraid of 12 Volts. Just think about this - if you wear a wrist strap to ground while the computer is unplugged, then the chassis is at a different potential (floating) than the strap - and it could discharge through the RAM. Not a good situation. Best to have everything grounded and no strap. – SDsolar Feb 3 '17 at 21:40
• Broadcast transmitters present a different problem: stored energy in the components. Even shutting down the circuit breakers does not guarantee safety, and no strap will save you if you let a tool or screw drop into the wrong place. I have had flash blindness from this due to a faulty bleeder resistor. Lost a precious 15 minutes just recovering before hunting down that problem so I could get back to business. Left hand was behind my back where it belongs. I am retired now, and never got electrocuted, even though I prefer to work on live circuits. You get better scope readings that way. – SDsolar Feb 3 '17 at 21:44