Introduction: Grounding an ESD Mat and Wrist Band at Home.
Electrostatic discharge is no laughing matter. The discharge voltage can reach tens of thoushands of volts, although it is low amperage. It usually takes several thoushand volts before humans can feel the discharge, such as walking across carpet with socks and touching a metallic surface. As little as 3 volts can damage components such as microprocessors. I will show you how to ground yourself and work surface at home. I was able to achieve this for under $5 as I used items that I already had. You can buy a kit that has everything you need but you will still need to follow the instructions for hooking up to ground. Let's get started.
*****DISCLAIMER*********
You should make sure that your home has proper grounding before attempting this instructable.
Materials:
Esd mat- we used to buy this by the roll at a previous employer so I had a small piece
Wrist Strap and cord- again already had this from a previous employer
Female banana plug
Ring terminals (qty 2)
Grounding household plug
Machine screw w/NUT- I used 1/4"x20x1"
Washers (qty 3)
Heatshrink -this is optional I just think that heastshrink makes things look a little nicer.
Wire -I used 16ga
The images are in order by step.
Make the wrist strap adapter.
If you buy a kit it will come with a hub that attaches to the mat via a snap, when the mat is on a roll it will not have this snap, so I just used items that I already have. Strip the wire and crimp a ring connector to one end , strip the other end and solder it to you banana plug. I used heatshrink over the post of the banan plug and the ring terminal.
Make the ground interface.
Remove the AC blades from the plug so no one gets shocked. Cut the wire to length ,strip both ends. Attach one end to the ground post terminal on your plug. Crimp a ring terminal to the other end again use heatshrink if you would like.
Grounding the mat and wrist strap
You can decide where to insert the bolt depending on your space. I chose the upper right corner as I am right handed. Used an Xacto knife and cut a slit vertical and the another horizontal making a cross , yes you can use other means but this is what I did. Place a washer on the bolt then insert the bolt through the mat from the bottom side up. Place another washer on the bolt. Now take the grounding plug and your wrist strap adapter and slide the ring terminal ends on the bolt. Place another washer on the bolt and use the nut and hand tighten.
Making the connection
Now plug the grounding plug into the ground on your receptacle, no risk of shock as there is no AC. Plug your wrist strap up and your are nowgrounded as log as you are strapped in.
Testing
Take a multimeter and test your wrist strap, you should have somewhere around 1M ohm resistance. Now, test from your wrist strap to the plug and ensure you don ot have a dead short. Now check from the grounding point on the mat to your earth ground you should have less than 1 OHM resistance according to the ESD Association.
Remember to never work on anything live even low voltage , I know this is one of the first things you learn but we are all guilty of it at some point
I hope this writeup comes in handy and saves some components from ESD. Thanks goes to Mik for his comment which made me realize a few things need to be added.
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10 Comments
6 years ago
Unfortunately I wouldn't follow your advice as it is quite dangerous
what you're suggesting. The reason being is that there is no protection
from your mat to ground (it's a dead short). So if something goes wrong
working on mains voltage gear - poof - you're dead. Yes I know you said
don't work on live equipment - sometimes it's unavoidable. The fact
remains - it's dangerous what you propose.
What you should do is
connect your mat to ground via a 1M resistor. The wrist strap should
also be connected to this ground point. Then go from that ground point
to your mains earth. Much safer and the correct way of eliminating
static discharge.
Here's a link - have a read on how to do it
correctly (sorry won't let me put direct links in) Search esdjournal for
grounds/fsg.htm
9 years ago on Introduction
Nothing about the clothes ?
10 years ago on Introduction
I have my electronic desk in my basement. I clip my wrist strap to a wire attached to a ground clamp on a pipe. I wonder if a Zener diode could be used, to make sure that any static goes one way.
11 years ago on Introduction
I see no mention of the very important series resistors here. If you are constructing your own ESD straps or body attachments read on :-
Most ESD wrist straps, strap cords, or official "earthing point" plugs have a series resistor somewhere to reduce the rate at which static "bleeds off" you and the circuit. But more importantly, to stop you getting a serious electric shock.
"no risk of shock as there is no AC" is not quite true. You have just deliberately earthed yourself via a nice low impedance path. If you accidentally touch anything live you are increasing the effect of an arm-to-arm shock. I know -- don't touch anything live ... but accidents happen!
Testers exist for wrist straps to make sure the series resistance is in the right range. Too high, it doesn't provide protection for ESD, too low and it creates a safety hazard for the user. If you don't have a tester, use a multimeter on the
"megohms" range and make sure that from the end that touches YOU to the end that touches mains earth is NOT a short circuit direct connection.
I have a "proper" ESD strap kit here - the wrist strap is 0 ohms from skin contact to the button. The lead has 1.2Meg resistor built in. The 4mm socket earthing point on my PSU is 0 ohms to mains earth. I wouldn't replace the lead with a simple wire!
Reply 11 years ago on Introduction
MIKB
The 1M ohm resistor is not a a requirement by the ESD Association, some manufacturers will place a 1M ohm resistor for current limiting purposes, which my wrist strap does have I did not mention anything about making or replacing the wrist strap with a "simple wire" for this reason, but I understand some people may not take that advice and try and make one without the resistance. My setup meets specifications set forth by the ESD association.
The mistake I made was assuming everyone has a proper electrical system in their house. I will add the requirements and the testing procedure to the instructable. Also the risk of shock that I was referring to would be form the AC plug. As everyone should know, nothing should be worked on live. We have all done it though but if you are going to work on anything that is live and has enough voltage to cause serious harm then you should know what you are doing. I guess I put common sense into to play on a daily basis but some may not.
Thanks again
Reply 11 years ago on Introduction
If you work with this stuff on a daily basis you can tend to forget the "obvious" stuff :)
I'm amazed the resistor isn't required by the ESD association, the testers we used to use at work would error out for "too low" as well as "too high" resistance when you clipped onto them and touched the test panel.
P.S. It's not just about working on live equipment, but the additional risk of you being HARD earthed by one hand and touching anything else that may have malfunctioned, totally unconnected to whatever you're doing!
11 years ago on Introduction
Do people have a lot of issues with static electricity and electronics anymore? I know the early series CMOS stuff was very sensitive but I've noticed a vast improvement over the past 20 years or so. Granted if you're running around on your synthetic rug with wool socks on you may build up a substantial charge and then I can see damage happening but I don't think normal levels of static are a concern today.
Personally I can't stand wrist straps and wearing one makes me clumsy to the point where I'm going to do more damage than they're ever going to protect me from causing. So no, I don't use them myself. If I think I have static build up I just touch something grounded before handling sensitive items.
You're better off with a humidifier.
Reply 11 years ago on Introduction
I am used to wearing wrist straps, as I have worn one just about everyday for the past 6 years, at work. Yes ESD is still a concern today, yes some components can take a little more than others. Humidifiers alone will not prevent static discharge.
Reply 11 years ago on Introduction
Dang, I'd think you'd have upgraded to an ankle strap by now! A little more? Uh huh.
Reply 11 years ago on Introduction
If you work in a lab that complies with Mil standard you would see how much effort is taken to prevent static build up. Yes we wear heel straps on an elevated grounded floor....