ESD mat earth connection - Page 1
Forum section: electronics / beginners

author: metebalci
author_rank: Frequent Contributor
timestamp: February 11, 2021, 05:14:24 pm
content: I have just installed my first ESD mat. So the ESD mat is connected to the earth bonding plug adapter which is connected to the mains earth (I live in Switzerland and I know at least the apartment has proper earthing specifically TN-S).I saw in a youtube video, someone was connecting the ESD mat to the ground terminal of the lab power supply. I dont have ground terminal in front in my supply but I have ground terminal at the back. Is this method the same or does it have any pros or cons ?I still feel strange about being connected (even through resistors) to the wall plug and I would like to install a tester or a monitor as well. Is a continuous monitor enough to give alarms in case of any issues ?Thanks.Mete

author: madires
author_rank: Super Contributor
timestamp: February 11, 2021, 05:49:43 pm
content: Electrically it doesn't matter how you connect the ESD mat to PE, i.e. via some lab PSU or directly by a mains plug. Just make sure that you have a 1M resistor in series for each mat or wrist band to limit the current to earth and between all ESD protection gear. If you use a mains plug remove the live and neutral prongs, just to be safe. Grounding via a lab PSU's earth/ground terminal has the drawback that you could lose the grounding when you move the PSU around or need to ground a DUT via the PSU. So a dedicated mains plug would be safer. Unless an earth/ground monitor is required for QA reasons or special applications I wouldn't bother to spend money on that.

author: ogden
author_rank: Super Contributor
timestamp: February 11, 2021, 05:54:23 pm
content: Metallic enclosures of most electronics devices are connected to mains earth and you don't mind that, so you may relax about ESD mat connection too. Ground terminal of any device shall be used only for grounding that device, never other way around. Connect your ESD mat using "ESD grouning plug". ESD chair would be better investment than ESD tester if you want to spend your money by all means.

author: metebalci
author_rank: Frequent Contributor
timestamp: February 11, 2021, 06:09:21 pm
content: Many thanks for the info and recommendations. The plug I am using has the insulated/plastic plugs for live and neutral and has 1M, so that is fine in that regard. But thanks for reminding about 1M, I did not realize that would be needed if PSU ground is used (which I will not use but anyway).

author: Ian.M
author_rank: Super Contributor
timestamp: February 11, 2021, 06:22:34 pm
content: The one megaohm series resistor is to limit the touch current to under 1/4mA if you get yourself between the mains supply and the mat, ESD protective wristband, etc. to prevent electric shock.Also, if you *ever*work on mains equipment and you are doing your own ESD grounding wiring, and need to fit a 1Meg resistor, use 2x 510K resistors or 3x 330K resistors in series to ensure it has enough voltage rating for it *NOT* to break down if the item it provides the ESD ground to comes into contact with Line of a live mains circuit.

author: madires
author_rank: Super Contributor
timestamp: February 11, 2021, 08:06:59 pm
content: ... or use 1 or 2W resistors rated for 500V or higher.

author: harerod
author_rank: Frequent Contributor
timestamp: February 12, 2021, 08:13:01 pm
content: Cascading several resistors has the additional important benefit of enhancing your chances of survival, should one resistor fail as a shortcircuit.@metebalci: Excellent timing. With the low outside temperatures causing low absolute humidity, it is that time of the year, when lots of electronics die from ESD.A few days ago I was remote guiding two guys installing PCBs in a new machine, 500km away in Basel. They worked in the conference room, not in the electronics lab, to facilitate video conferencing with several cameras. Long story short - I guess they fried one board with ESD, because of insufficient protection. Well, scrap a few k€ worth of time and hardware, next week we try again, under more carefully controlled conditions. ESD may be a tricky problem, because it can cause multiple types of errors, performance degradation and eventual early device death being among the worst.