Read this first!
Despite the fact I am a Senior in Computer Engineering (which carries a lot of Electrical Engineering with it), all information provided here is only for hobbyist purposes and Hallman Labs is not liable for your mistakes. There are potentially LETHAL voltages at play, should you connect to something other than the outlet ground. You will notice, there are no wiring/outlet diagrams shown at all on this page. This was purposefully done, for both our sakes (see links below).
For this reason, Hallman Labs assume no responsibility if you read the Q/A and do something to harm yourself or your circuit. Before you do any of what is mentioned, please do the proper research and do not try and skip ahead. While this can be used as a cheat sheet, it should not be used as your sole ESD reference.
With that said, I did everything I could to ensure this was written in a way that you would have a hard time following it and getting yourself hurt. I pretty much included all the caveats to wiring ESD protection. I also included the best ESD references I found during my research, at the end of the document.
I have read questions like these more times than I care to count. It seems many people lack the proper understanding of ESD protection and why/when it’s used.
TLDR: In this case, you need to read the entire document, for the safety of yourself and your circuits.
Question 0: What is electrostatic discharge?
Electrostatic Discharge (ESD) is an electrical phenomena where voltage spikes appear between two bodies of differing electric potential. The discharge occurs one of three ways: direct contact, dielectric break down (arcing through the air), or a short circuit (never good to have in a circuit). The most famous example of this is in lightning strikes, where the cloud and the ground/earth are the two bodies of potential difference.
The two principle causes of ESD are: static electricity and electrostatic induction. Static electricity just means there is a voltage discharge between two potentials, due to contact or dielectric breakdown. Electrostatic induction operates on the same principles as any sort of induction. Without having to actually make physical contact with an object, induction redistributes charge around the body (to an imbalanced state). This induces a voltage due to this new arrangement of charge.
Question 1: Do ESD straps/mats protect the technician from voltage spikes in the circuit itself?
No, it doesn’t. ESD only protects the circuit from your discharges. Which is the same discharge you get from touching a door knob in dry weather. This is the entire purpose of ESD protection and nothing more.
Question 2: Is it really okay to plug myself directly into the outlet’s ground pin?
The short answer is yes (remembering the 1M-ohm safety resistor in the wrist-strap itself). Before you even attempt to do this, I highly recommend buying a $5-$10 3-prong outlet tester, such as one of these. This way, you can ensure the wiring is safe, before you hook your ESD strap to it. Without this step, you are essentially putting your life in the hands of the electrician who wired the outlet.
If you want to be able to hook up directly to the outlet’s ground, you’ll need to purchase a plug specifically made to connect only to the 3-prong’s ground (the round pin). You can find a kit from Amazon for $30 that includes such a plug right here. I own this same ESD system and use it for all of my ESD strap connections. This one does connect more than just the ground, but this is done in a safe way.
Important note: this is something I wouldn’t recommend doing as DIY. It’s just too risky and too cheap to buy one (that is known to be safe). If you want to go a purely DIY route, then just use the screw on the face plate of the outlet. Also, if you make your own ESD wrist-strap, be sure to include the 1 Mega-ohm resistor (all ESD straps have this for safety). See the diagram below for reference.
The key here is, you need to be sure you connect your ESD strap to something that has a strong connection to ground. On any outlet, the center screw that holds the face plate (between the two plugs) is always connected directly to ground (assuming the electrician built it to code). You could also connect to any chassis screw on most electrical devices, such as a computer or audio amplifier. It’s unlikely you’ll find a chassis that isn’t grounded. Although, you’ll need to have the device plugged into the wall in order to create the path to ground. Don’t forget this step, if you decide to hook up your ESD strap/mat to a chassis!
Note: You shouldn’t use the chassis of the actual device you are working on. It’s recommended to totally unplug and discharge the power capacitors (if applicable), much less leaving it plugged in. It’s never a good idea to leave something plugged in while working on it, unless absolutely necessary in order to diagnose.
Question 3: What circuits are most susceptible to damage from ESD?
One rule of thumb: the smaller the circuit elements, the higher the chance you will damage them from electrostatic discharges (ESD). This is pretty intuitive, considering the smaller the component is, the less current it can handle. This is due to the fact that the physical dimensions of electrical components determine their current carrying capability.
MOSFET transistors have a very high input impedance, which means that the voltage is not dissipated. Due to the small size of transistors, the barrier between the conductor and insulator is very small. This makes it susceptible to high voltage spikes from ESD.
Below you can see an electron microscope image (provided by Analog Devices Inc.) of ESD damage to electrical traces on/inside the PCB. This is the sort of microscopic damage that occurs, which we have no way of seeing (in our home labs).
Question 4: Do I need ESD protection even if I am never getting discharges in my lab/work environment?
Yes, you do! Assuming you work on anything that uses surface mount components or transistors of any kind. When you hit a circuit with an electrostatic discharge, you are essentially inserting a short pulse of (static) voltage, which induces a short burst of current in the circuit (due to the resistance of the circuit elements and Ohm’s law).
For you to feel the discharge (like the classic doorknob example), the voltage needs to be between 2000-3000 volts. You might think this sounds awfully high, but remember how short of a discharge we are talking about. By the way, it’s the capacitance and resistance of the human body which determine the RC time constant, as ESD occurs!
The caveat, you are discharging ALL the time without even knowing it! Since it requires such a large spike for us to feel it, we don’t feel the majority of the discharges we create. On the other hand, our sensitive circuits may get ruined by a small 50 volt ESD spike (or less).
This means, that circuit you randomly killed last month, might have been hit by small ESD voltage spikes! I definitely recommend using ESD protection when dealing with any computer parts, especially if doing anything involving touching the motherboard, CPU, GPU or RAM (anything with exposed contacts or PCB itself).
If you’d like to know more, see the links below.
The Lazy Man’s/HL’s ESD and 100% Safe:
The following is the method I used my entire life until the last five years or so, since using dedicated ESD wiring. I have yet to knowingly shock a piece of hardware, so it obviously is effective and requires no extra work.
It relies on the same principles we already discussed, how nearly all chassis are grounded (*knock on wood*). This is all you need in the vicinity of your workstation. Then, just before you go to touch the circuit, touch the grounded chassis first. If you don’t move your feet at all, you likely don’t need to repeat the process.
Preferably you want to touch an unpainted metal surface on the chassis. Here are a few examples of where to touch:
- Back panel of an amplifier: the AM antenna hookup or the RCA jacks.
- Any BNC Input Jack, on the outer ring.
- The bottom of a metal chassis, on the inner side is likely unpainted.
- Anywhere you see a screw running into a piece of sheet metal (of a chassis/enclosure) with a wire coming off of it, that is a ground (check to be sure with VMM).
This will remove any large excess charge off of your body. Note: you can immediately build it back up without having a grounded strap on.
I also found this on Amazon recently:
References and Additional Reading on ESD:
Out-of-Circuit Overvoltage Protection From ESD
Electrically Induced Damage to Standard Linear Integrated Circuits