I bought 2 anti-static gloves and 1 grounded wrist strap to protect the parts against ESD by assembling computers. I was wondering whether a single wrist strap is enough, because I use to touch parts with my right hand too.
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1\$\begingroup\$ Even the ankle strap should be enough... \$\endgroup\$– Eugene Sh.Feb 22, 2018 at 19:18
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1\$\begingroup\$ depends on your definition of enough. \$\endgroup\$– Trevor_GFeb 22, 2018 at 19:19
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3\$\begingroup\$ Unless you're in a really dry environment on nylon carpets. Humans are conductive enough that a single strap will drain charge effectively. \$\endgroup\$– pjc50Feb 22, 2018 at 19:20
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1\$\begingroup\$ You might need an ESD Hat too. Works even better if you line it with tinfoil. ;) \$\endgroup\$– brhansFeb 22, 2018 at 19:30
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1\$\begingroup\$ Is whatever you are working on also grounded? By means of ESD mat? \$\endgroup\$– Jeroen3Feb 22, 2018 at 19:31
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4 Answers
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Grounding yourself is only part of mitigating ESD. You can still cause damaging discharges while properly grounded when the device you're working on is itself charged, when the tools you use (like a multimeter or screwdriver) are carrying a charge or when your workbench/parts bin is charged.
Ideally you'd ground everything that can come into contact with sensitive devices:
Yourself
Any surfaces where you may lay down your board and/or components
Any tools and equipment that may contact the device (soldering irons, electronic test equipment, screwdrivers, etc.)
This grounding can be accomplished either through your body (as is done with a dissipative screwdriver, side cutters and the like) or a dedicated grounding wire (e.g. an antistatic mat on your bench). Grounding leads must contain a high value resistor, so that you won't get shocked via your strap when accidentally coming to contact with high voltages. Grounded surfaces should be resistive (e.g. ESD mat, dissipative tray), instead of highly conductive (e.g. steel box, aluminum plate), so that any discharges that do occur will get current limited.
Do you really have to go through all this trouble? It depends. I personally don't bother taking all these precautions with hobby electronics or while taking my PC to bits (at my own risk). However, I do take this seriously at the workplace and I think you should do the same.
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\$\begingroup\$ While this is really useful, it does not answer the original question, but probably some of the comments do. Let me ask something. If I have a wrist strap like this: ultrastatinc.com/… I guess it does not contain the "high value resistor" part, so does it mean it is useless against ESD, or it just means reduced protection? \$\endgroup\$– inf3rnoFeb 22, 2018 at 19:52
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5\$\begingroup\$ @inf3rno From the page you linked: "Cords contain built in 1 meg ohm safety resistor". It's standard practice, I doubt that you'd be able to find straps without a resistor in them. \$\endgroup\$– jmsFeb 22, 2018 at 19:53
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\$\begingroup\$ Can you add that part from the comments, that a wrist strap is enough on a single hand and not needed on both hands to ground somebody? After that I can accept this answer. \$\endgroup\$– inf3rnoFeb 22, 2018 at 20:00
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1\$\begingroup\$ @inf3rno your body is about 200pF. Even with a 1M resistor, it would discharge in under a millisecond. The purpose of the 1M resistor is to stop you electrocuting yourself if you accidentally touch something live (e.g. mains voltage). \$\endgroup\$ Feb 22, 2018 at 20:04
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6\$\begingroup\$ @inf3rno You only need a single wrist strap, pretty much anywhere on your body will do. Just make sure that it does its job, the conductive threads in them don't last forever in daily use. In manufacturing and R&D environments you'll often find purpose-built testers that make sure that your strap (and antistatic shoes) are in working order. \$\endgroup\$– jmsFeb 22, 2018 at 20:05
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As the question written, "is one wrist strap enough", the answer needs some qualifications.
If you are concerned about touching parts with your other hand, then the body conductivity will provide discharge path for the entire body even with one wrist strap. So the answer is "YES".
However, this answer assumes that the rest of assembly environment is designed in full accord with ESD protection methods. Ideally, you need a ESD mat, and an assembly table with ESD-qualified surface, all properly grounded with leads having 500k+500k "safety" resistors. Check with some articles on ESD protection how to accomplish this.
answered Feb 22, 2018 at 20:18
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\$\begingroup\$ Thanks Ali! I already accepted an answer and I don't like to change that, but I'll have another question later about ESD and soldering. :-) \$\endgroup\$– inf3rnoFeb 22, 2018 at 20:20
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\$\begingroup\$ @inf3rno, your future soldering question already has an answer, electronics.stackexchange.com/a/268990/117785 :-) \$\endgroup\$ Feb 22, 2018 at 20:23
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\$\begingroup\$ I have already read that, but thanks! :-) It will be related. \$\endgroup\$– inf3rnoFeb 22, 2018 at 20:41
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\$\begingroup\$ Posted, but it might not meet the standards of this site. \$\endgroup\$– inf3rnoFeb 22, 2018 at 22:56
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There is really no answer to this question as written. Since ESD protection is really a probability thing, "enough" is meaningless.
There are also many variables that affect how much ESD you may be carrying. What you are wearing, what kind of shoe or sock you are wearing, carpet or tile, dry air or humid, dry skin or moist, hairy wrist or bald, how much you are moving around... it all affects the formula
Enough also depends on what you are working on. Some devices are relatively insensitive to ESD. Others are so sensitive you need to work under ionized air.
In general, if your wrist strap is making good skin contact, you are pretty safe to work on general electronics. However, it doesn't hurt to get into the habit of touching something grounded with the other hand before you unpack a device or touch a circuit board.
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\$\begingroup\$ Enough = computer parts are not damaged due to ESD. If you want probability, then <1/10k damages due to ESD. These are mostly PC parts, not workstation or server grade parts. The temperature is 20°C, relative humidity is around 30-40%, I think you can guess the pressure. \$\endgroup\$– inf3rnoFeb 22, 2018 at 19:40
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\$\begingroup\$ @inf3rno ya but the point is that it is a matter of degrees. One part may be good for one level of ESD, another.. not so much. The more ESD protection you use the less probability of damage. There is no such quantifiable thing as "enough" for all circumstances. \$\endgroup\$– Trevor_GFeb 22, 2018 at 19:42
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\$\begingroup\$ I am pretty sure the parameters are quantifiable, and I guess there is already a literature of such tests, measurements, scientific experiments, I just did not read them and I don't want to become an expert in the topic, that's why I am asking here, maybe somebody have an answer. \$\endgroup\$– inf3rnoFeb 22, 2018 at 19:46
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\$\begingroup\$ @inf3rno you might think so, but in reality, it's hard to quantify this shirt vs that one, etc. It comes down to numbers more like... 1000 people tested with a strap 1000 didn't, of those that did, the device failures were 70% less than those that didn't. \$\endgroup\$– Trevor_GFeb 22, 2018 at 19:51
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\$\begingroup\$ I found that there are ESD simulators/generators used for testing purposes, e.g. testing a part for ESD immunity. It is surprising that I could not find any publications about experiments/tests. I guess the manufacturers wants to keep the results for themselves and nobody wants to conduct independent experiments in the topic. Or it just takes a lot more time to find such articles. \$\endgroup\$– inf3rnoFeb 22, 2018 at 20:39
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One grounding point on your body is sufficient to drain any charge on your skin. We are not insulators, our skin is conductive and any static electric charge on your body will equalize over your entire body within microseconds.
You can dispense with a ground strap entirely by using ESD conductive shoes and working on a conductive floor or ESD mat that is grounded, and using a grounded ESD mat on your work bench. It is also advisable to wear an ESD smock over your clothing, as your clothing is actually one of the the primary sources of static charge.
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1\$\begingroup\$ ESD shoes won't offer sufficient protection when you aren't putting enough pressure on the soles of your shoes (as when sitting down) and ESD chairs alone are not effective enough. You should still plug in your wrist strap whilst sitting down. Disclaimer: this is what three employers in the industry have led me to believe, but it certainly shouldn't be taken as fact on that basis. You are welcome to prove or disprove this. \$\endgroup\$– jmsFeb 22, 2018 at 21:56
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\$\begingroup\$ Well, I certainly can't prove it to be sure. I worked in manufacturing test department for 10 years at Beckman Coulter and that was our standard. ESD shoes on a conductive floor or heel straps with regular shoes was required (along with an ESD smock). In general if you were sitting with feet flat on the floor it was allowed, if your feet were not on the floor you had to be grounded with a wrist strap. It seems its something that varies from one employer to the next. \$\endgroup\$– NormFeb 22, 2018 at 22:36