ESD Grounding Question - Page 1
Forum section: electronics / beginners

author: Mp3
author_rank: Frequent Contributor
timestamp: March 04, 2018, 08:09:11 am
content: OK guys,For many years i have been in the camp of "don't need to use ESD protection because i've never broken anything yet." For things i was very worried about I got some anti static gloves on amazon, but learned they might not do the trick always. I looked into it some more and realized that is not a smart position to take, so i've also got some ESD bracelets now. I have two questions i'm not 100% clear on.1. For devices which have a plastic enclosure, what to attach the ESD bracelet to?2. Are you only protected if you're grounded to the device you're working on, or is something else which is earthed acceptable too for the +0v?

author: Vtile
author_rank: Super Contributor
timestamp: March 04, 2018, 09:40:34 am
content: Well, since no one else have answered anything I'll mix this soup with my ramblings.When you are dealing with the static electricity you are facing different kind of physical phenomenas than normal conductor based electricity. These are charged particles in surface of objects or inside the material itself or ions in the fluid around them. The object as such is anything in your working space.So ideally you would work in a conductive box wearing a conductive suit. Since we would want to have every object to be electrically connected through big enough conductance.Now we can wait someone to give you a real answer.

author: ogden
author_rank: Super Contributor
timestamp: March 04, 2018, 11:25:30 am
content: There are different levels of ESD protection. You shall decide how ESD-safe you would need/want to be. It depends on how often you work with ESD-sensitive devices and how much they costWear plain cotton, make sure all your instruments including soldering iron are earthed, use ESD bracelet and earthed ESD mat on the table. Next level is ESD footwear and chair, ESD-rated tools (screwdrivers, tweezers and so on), waxing floor(s) with anti-static wax, air humidifier if dray air. Then comes ESD coats, ESD floor vinyl

author: Fludo
author_rank: Regular Contributor
timestamp: March 04, 2018, 12:33:15 pm
content: The ESD rabbit hole goes very deep and is very expensive. Our workstation we bought was $25k with including irons, hot air, lighting, and microscope. You will be fine for personal work using a wrist strap and ESD mat. Make sure the iron says ESD safe and has a grounded tip. A set of ESD screwdrivers is generally a good idea when connecting things to circuit boards.The strap will give you a high impedance ground to dissipate charge from your skin, and the mat will do the same for any objects on it. Try to keep paper, plastic, and foam off the mat.

author: Shock
author_rank: Super Contributor
timestamp: March 04, 2018, 01:29:28 pm
content: This tutorial looks ok to get you started. Don't go near the mains though with your multimeter unless you have like suggested, a safe multimeter and experience in how to remain safe.You can alternatively connect the antistatic mat strap to the earth connection on your power supply or an earthed chassis of any test equipment you have plugged in permanently. Good idea to get an earth leakage or RCD type device for your benches mains outlet as well. If you do get one installed you can get the electrician to check the outlet for good earth and install the strap if you need help.

author: Mp3
author_rank: Frequent Contributor
timestamp: March 05, 2018, 01:06:28 am
content: Ok thanks for all the replies, but what are you supposed to ground yourself to if the enclosure of the thing you're working on is plastic and powered by an AC (not DC) wall wart?I know that ESD is a rabbit hole that can go very deep but what i have to work with is ESD safe gloves from Amazon and ESD wrist strap. Please help me do the best i can do with what i have. I know about proper conditions including humidity etc, but i don't know what to do with the esd bracelet when there is no obvious ground.The PCB is sensitive, the enclosure is plastic and the source of power is an ungrounded wall wart. No, i do not have a grounded 9V AC supply.

author: FrankE
author_rank: Regular Contributor
timestamp: March 05, 2018, 06:21:49 am
content: I've a plastic plug that goes into the wall socket. The L&N pins are plastic, only there to open the earth shutter and provide mech support. The strap clips on the front.I've also a manifold block which incorporates a resistor. I guess it can be connected to any equipotential grounded point.

author: ogden
author_rank: Super Contributor
timestamp: March 05, 2018, 09:44:05 am
content: Quote from: Mp3 on March 05, 2018, 01:06:28 amMost likely device is not that big, right?Anyway - in this case you must have earthed ESD mat and earthed bracelet. When you start your work - put device on a mat and take a second. It will lose surface charges quickly, if any. When device is on the mat there's no way for charges to build-up because of mat, gloves and bracelet. That's it. Those who work on mobile phones even in assembly factories where ESD is top-notch, do not earth themselves to device as well. There are loads of consumer device assembly videos on youtube, you can learn a lot from them in this regard. Search for instance "iphone assembly".There'sgoogle as well.

author: Shock
author_rank: Super Contributor
timestamp: March 05, 2018, 10:06:29 am
content: Quote from: Mp3 on March 05, 2018, 01:06:28 amTL:DR - You're doing it wrongThe ESD mat, wrist strap is always connected to a real ground. This prevents you building static charges and discharging through the circuit.The alligator clip for connecting to a metal chassis is for convenience. The chassis still has to have a good ground connection. Through a connected power cable for example (see below).If there is a static build up on the plastic enclosure, after your wrist strap and mat is properly grounded just handling it will discharge it.For circuits if you want them at the same potential as your ground you can make a connection between the ground and the negative or common side of the circuit and keep it in place while servicing.For safety don't ever clip a wrist strap (or use a wrist strap) in a situation where you have live/energized circuits. So for a clip on wrist strap the device needs have a good chassis to ground connection, to be switched off at the mains outlet, but still be connected to have a good earth/ground present.

author: Mp3
author_rank: Frequent Contributor
timestamp: March 05, 2018, 10:12:06 am
content: Gonna buy an esr mat now then. Thanks everyone! I was confused about the enclosure being plastic!Something better than this for the money?https://www.ebay.com/itm/3-Layer-Dissipative-Vinyl-Anti-Static-ESD-Mat-W-GROUND-CABLE-18-X-24-Grey-/272289662932

author: alexinokotoks
author_rank: Newbie
timestamp: March 05, 2018, 04:10:19 pm
content: Hi there! New here, as in just registered. One thing about ESD damage is the latent type. Lets say you are working on a project without ESD protection in place. Finish your project and yep it works. However a few days/weeks/months it fails for no reason. You can damage a component through ESD discharge but not kill it only weaken it. This is a big issue for CMs (contract manufacturers) who have shoddy ESD practices.Alex

author: Vtile
author_rank: Super Contributor
timestamp: March 05, 2018, 04:33:28 pm
content: Quote from: ogden on March 05, 2018, 09:44:05 amNot entirely correct, since the plastic surface can generate triboelectric charging (=search tip for OP) and depending the material it can stay partially charged. You can easily measure (see the effect) these charges if you happen to have a volt meter with greater than 100Mohm input impedance and short piece of leads on the connectors.You can even create the charge with some plastics while rubbing the surface with the tip of the meters probe.

author: BillB
author_rank: Unknown
timestamp: March 05, 2018, 04:41:30 pm
content: Quote from: Mp3 on March 05, 2018, 10:12:06 amIf you are going to do any soldering on the mat, then rubber might be preferable over vinyl though they are more expensive. In the past I have purchased rubber mats from that same vendor and they seem like good quality.

author: GeorgeOfTheJungle
author_rank: Super Contributor
timestamp: March 05, 2018, 06:34:55 pm
content: You may already know this but just in case...The bracelet protects the thing you're working on, not you. To protect you, you'd better be floating in isolation, not connected to anything, not even to GND. But the bracelet connects you to GND.In the past, when the displays were CRTs, the service manuals had a big warning saying do NOT wear an ESD protection bracelet when working on CRTs (or on anything with high voltages). Later on when the SMPS power supplies became common, (late 70's) most came with the same advice/warning.I don't know how much current can pass through the resistor of a good ESD bracelet before if breaks open, I'd guess it shouldn't be much, but just in case, if the warnings were there I suppose it was for a reason.So to be clear: your chances of electrocution are higher with the esd bracelet than without it...

author: Mp3
author_rank: Frequent Contributor
timestamp: March 05, 2018, 07:39:46 pm
content: Quote from: BillB on March 05, 2018, 04:41:30 pmThanks for this!I have been de-staticing myself for years by touching my computer's power supply. I worried it would transfer static thru my power supply and weaken it, but the same machine i was using when i learned this "trick" still works like a charm....I have a rubber mat on order, but the mats they sell that don't come with a grounding point, do they expect you to add your own? It seems like there is not a lot of reason to use one without a ground point attached. Do some of them not come with those in case you have your own ground point?Quote from: GeorgeOfTheJungle on March 05, 2018, 06:34:55 pmThanks for this but i'd rather take a little zap than the gear i'm supposed to be fixing!

author: chriswebb
author_rank: Unknown
timestamp: March 05, 2018, 07:47:35 pm
content: Quote from: GeorgeOfTheJungle on March 05, 2018, 06:34:55 pmCan you explain this a little better, because I am having a hard time understanding what you are saying. Warning labels aren't necessarily proof of something being inherently dangerous. They could be used purely to prevent liability. So really haven't established proof that wearing an ESD bracelet is harmful. Just that makers of those products don't want you to.Also I am just purely not understanding how its more dangerous than without it.Seeing as you are basically adding a 1M ohm series resistor in between the live wire and your body. The current still has to pass through your body to ground so will be limited by the current there, most current choosing to take the direct path to ground rather than going through the body anyway. But the bracelet isn't the only thing connecting you to ground. Your feet do that too, or your chair so most people probably cant isolate unless they actually float. So really isn't the important part the wire that connects the wrist strap to ground and not the wrist strap to you through the 1M ohm resistor?Can you provide some data or some research into this? I am probably just missing something simple...Also not sure if I explained my confusion adequately, I can go back over what I'm trying to say when I have more time later..

author: helius
author_rank: Super Contributor
timestamp: March 05, 2018, 08:49:37 pm
content: The 1M resistor in the wrist strap is not capable of holding off EHT voltages from CRTs. In fact it probably is only rated for 1KV?It's also what happens if it gets snagged or cut. If you have your hand wrist-deep inside a CRT set and the conductive thread makes contact with the flyback...or if the cable gets nicked...

author: chriswebb
author_rank: Unknown
timestamp: March 05, 2018, 09:29:05 pm
content: Quote from: helius on March 05, 2018, 08:49:37 pmI was still questioning this, but I think my confusion might stem from the fact that I may be overestimating/not understanding the bodies resistance. I also probably shouldn't be applying Ohms law as strictly here, since the body isn't a normal conductor. Thanks for the further explanation! Still curious about some things, may be a good idea to come up with some safe experiments (not high voltage!!!)

author: ogden
author_rank: Super Contributor
timestamp: March 06, 2018, 11:23:54 am
content: Quote from: chriswebb on March 05, 2018, 07:47:35 pmI wonder why would anyone need to wear ESD bracket when working on CRT. Do you wear ESD bracelet when you work on your tesla coil driver? It's in the same category as warning "do not dry your pet in the microwave oven".

author: GeorgeOfTheJungle
author_rank: Super Contributor
timestamp: March 06, 2018, 11:46:16 am
content: Quote from: ogden on March 06, 2018, 11:23:54 amNot all the CRT displays were analog, b&w and with valves...

author: chriswebb
author_rank: Unknown
timestamp: March 06, 2018, 05:45:26 pm
content: Quote from: ogden on March 06, 2018, 11:23:54 amYou are in the beginners section, mate. I don't touch anything with High Voltage. Things need to be explained if they are to be understood.

author: Shock
author_rank: Super Contributor
timestamp: March 06, 2018, 09:23:45 pm
content: Quote from: chriswebb on March 05, 2018, 07:47:35 pmIt's common sense in bench safety not to connect yourself directly to a high energy circuit, it adds another element of risk. You can surmise all day over it would be safer this way or that way. With a nice air gap between you and any mistakes you make, current has a far harder time flowing.When it comes to SMPS, TV, Microwaves and CRTs the warning labels ARE there to show inherent dangers, so much so they put drawings and lines on the PCB and little stickers on heatsinks and outside showing you.You gotta remember all the pioneers of stupidity died yesterday so we can have a safer today.