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I've watched the recent video of LTT with ElectroBOOM (The SCAM of Wireless ESD Straps - Feat. ElectroBOOM) and they mentioned that the ESD wrist wrap is essentially there to protect you and the electronics from ESD.

I'm wondering if an ESD strap could save you or at least reduce the risk of being electrocuted from mains voltage by routing the voltage through your hand and the ESD strip to ground and not via your body.

The ESD strap used in the video has a 1 MΩ resistor built in. That should theoretically reduce the amperage down to 0.00023 A at 230 V which is less than 35 mA and reduce the risk of a cardiac arrest.

Little disclaimer: Being an emergency paramedic I know that this is totally stupid and should never be done, but I wondered if this would work.

Andrew Morton
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Pa0x43
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    No! If you are being electrocuted the current is not flowing on the surface of your skin. – John Birckhead Apr 14 '23 at 18:19
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    The ESD strap isn't to protect **you** from ESD. It's to protect the stuff you're working on from **your** static electrical charge. If you happen to get zapped less often in the process, that's just a happy (for you) accident. – TimWescott Apr 14 '23 at 18:30
  • I know very little about this subject, so have a question for the people answering this question: couldn't the wrist wrap theoretically protect you by providing a path to the GFCI (ground-fault circuit interrupter) ? The way I am thinking of it is as follows: when you are ungrounded, you touch one pole of the mains with your left hand, nothing happens; you touch the other pole with your right hand, you are dead. However, when you are grounded, you touch one pole, the GFCI immediately drops. – Mike Nakis Apr 15 '23 at 09:05
  • @MikeNakis Good answers in the thread. You could also see [this old answer](https://electronics.stackexchange.com/questions/265920/should-there-really-be-1-m%e2%84%a6-resistance-between-an-anti-static-wrist-strap-and-a/265924#265924) of mine regarding the issue. – LorenzoDonati4Ukraine-OnStrike Apr 15 '23 at 10:05

6 Answers6

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It will not provide any protection. The goal of the ESD strap, as you mention, is to protect your workpiece from ESD by slowly removing charge from your body by providing a controlled, high-resistance path to ground.

This high resistance prevents the risk of one avenue of electrocution, which is electrocution through the ESD strap which connects you to ground, thus preventing the ESD strap from adding a new risk.

If you're unlucky enough to touch a 230V potential while grounded through some other connection (e.g. a grounded metal chair, other hand at ground, etc), you could still get electrocuted - 0.00023A through the ESD strap, and enough current to induce acute medical issues running in parallel through that other ground connection.

To avoid electrocution, you need a high enough resistance in series with any possible current paths. This would mean electrically insulating gloves, keeping one hand in your pocket to avoid a path across your hands, fiberglass (rather than metal) ladders, shoes with thick rubber soles, and safety tests/certifications on all of these measures.

Once you've assured that there's adequate insulation to protect the worker, then you can begin to worry about ESD protection to protect the workpiece, with enough series resistance (and a safety assurance that the resistor will never fail short) to limit the current that could flow through the worker.

nanofarad
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  • What about GFCI? (See my comment under the question) – Mike Nakis Apr 15 '23 at 09:26
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    @MikeNakis 230V/1 MOhm is too little current to reliably trip a GFCI. A GFCI outlet/breaker upstream of the workpiece and workbench is still a useful step for increasing the overall safety of the system, regardless of the presence of an ESD strap (which does nothing good or bad for safety when properly constructed). – nanofarad Apr 15 '23 at 15:18
  • I wonder if it would be useful or practical to have a sense circuit, connected to the strap with a series pairs of safety-rated 1M resistors, which woud trip a GFCI if there were any appreciable sustained voltage on between the wrist strap and ground. – supercat Apr 15 '23 at 20:54
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An ESD strap does not protect you from electrocution in any way.

WITHOUT a resistor, the ESD strap would be much MORE dangerous than wearing nothing. The reason being that at all times it's providing a low impedance path to earth from your body, which is half the equation with regard to getting electrocuted.

WITH the 1 megaohm resistor, the wrist strap is similar in safety to wearing nothing.

Drew
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No, you will get electrocuted, but the 1MegΩ resistor will prevent large currents and arcing if there is a short.

The 1MegΩ resistor makes the ESD strap "relatively safer", it also works the other way around if there is a ground fault on the ground line it can also help to protect equipment and people.

Voltage Spike
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An ESD strap with an integral 1 megaohm resistor is better than an ESD strap with a 0 ohm resistor (i.e. no resistor).

You may have looked up and seen birds perching on the medium-voltage (2000-9000 volt) distribution lines, and you think "why aren't the birds dead?" Well, they're only touching one wire, and it takes two to complete a circuit. So...

  • If you touch 1 hot thing and absolutely nothing else, you are a "bird on a wire".

  • If you touch 2 hot things at the same voltage, phasing and polarity, e.g. the 2 terminals of a switch that is on, you are a bird on a wire with 2 feet on the same voltage. No problem.

  • If you touch 1 hot thing while touching a) neutral, b) safety ground which is bonded to neutral, or c) another hot thing on a different phase or polarity (think two phases of 3-phase, or Philippine, British or American L1 and L2 poles)... then you will get shocked. If you have a 3rd connection via a megaohm ESD strap, this changes nothing.

  • If you touch 1 hot thing while grounded with an ESD strap that lacks a resistor, same result - you get shocked.

  • If you touch 1 hot thing while grounded via an ESD strap with a megaohm resistor, we have arrived at the situation you are asking about. The megaohm resistor saves your bacon.

Harper - Reinstate Monica
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  • Can you elaborate why (in your last point) ESD strap with 1M resistor will save you? I think human skin has resistance of about 100k at most (when dry) and down to as little as 1k when wet. So, even with 1M alternative path to the ground, shouldn't between 90% and 99.9% of the current still flow through human body instead of through ESD? – Matija Nalis Apr 16 '23 at 15:54
  • @MatijaNalis You're thinking of the 1 megaohm resistor as if it is in parallel with something else. I'm not sure what that would be. The 1 megaohm resistor will be in series with the ESD strap. – Harper - Reinstate Monica Apr 16 '23 at 22:37
  • I'm imagining user with ESD strap on left hand being connected to the ground via 1M. The user touches high voltage source with right hand. Current can go `right hand -> body -> left hand -> 1M ESD -> ground`, or it can go for example `right hand -> body -> legs -> ground`, right? What am I missing? What would be example where 1M ESD protects the user (and s/he would be unprotected without such ESD)? – Matija Nalis Apr 18 '23 at 00:53
  • @MatijaNalis I realize when we are not flying we call that "on the ground", and you might be confusing that with "having a quality electrical ground". Most of us work in shoes and a human-built floor, which provides for functional insulation against the unexpected. Someone expecting to be shocked should use better protective equipment. – Harper - Reinstate Monica Apr 18 '23 at 04:54
  • Thanks - I agree that (with careful and well educated user) path via foot to ground is not a electrical ground of "good quality" (i.e. low impedance), and I understand that people should wear shoes with big protective rubber soles etc. when working with dangerous voltages to reduce the risk of that path to the ground. But I am still confused in which situation exactly do you envision the 1M ESD would help to protect the user? Can you give concrete example (like I did above)? – Matija Nalis Apr 18 '23 at 23:14
  • @Matija I already said. `Hot -> right hand -> body -> left hand -> ESD strap -> 1M resistor -> ground`. Note how the 1M resistor is in series. – Harper - Reinstate Monica Apr 18 '23 at 23:28
  • But that example only **adds** risk as opposed to user having **no** 1M ESD strap at all, instead of **reducing** their risk? I.e. if in that the same example the user didn't have _any_ ESD, it would be `Hot -> right hand -> body -> ... nowhere? as there is no path to ground` so circuit would remain open and user would be (even if only slightly) **safer** because they ***didn't have*** ESD strap? Or what am I missing? In which example is user **more safe** while _"wearing 1M ESD"_ compared to _"not having any ESD at all"_? – Matija Nalis Apr 19 '23 at 00:07
  • Oh, or are you instead comparing situation _"ESD with 1M resistor"_ to _"ESD without any resistor"_ (instead of _"no ESD strap at all"_ which I seem to have understood)? – Matija Nalis Apr 19 '23 at 01:59
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    @Matija ah yes, that explains it. Yes, I was presuming that an ESD strap was required for the task, and was contrasting "ESD strap with 1Mohm resistor" to "ESD strap with 0 ohm resistor". The difference in safety between "1 Mohm" and "not wearing ESD strap" is negligible since 230V @ 1 MOhm will flow 0.23 mA which is not even detectable by human senses. Assuming the location of the resistor is competently chosen. – Harper - Reinstate Monica Apr 19 '23 at 02:11
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Well, you are correct in that the 1 megaohm resistor - as part of an ESD strap - is indeed a protection feature against mains voltage. But that resistor exists only because you are putting yourself in danger by strapping yourself to earth in the first place.

feynman
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The ESD strap is intended to provide a slow equalization of static charge between the human body and a workpiece through a 1 megaohm resistance. That's it. The workpiece does not need to be grounded. If ground is not available the wrist strap is connected to the chassis of the workpiece so that sensitive parts can be handled. Often when removing or installing parts the chassis of the workpiece is not or cannot be grounded. Static dissipative mats are intended to provide a slow discharge path to ground thus allowing the work surface to equalize with surrounding voltage. Placing a charged workpiece on the mat will allow the static charge to dissipate slowly.

The wrist strap is not intended to protect a body from voltages within the workpiece or other sources. Spark free voltage equalization is the only intended use.

RussellH
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