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I am looking to purchase some anti-static gear for when working on electronics(I'm assuming all electronics should be worked with on an anti-static pad, that's correctly grounded, correct?), and noticed in some reviews there are mention of not having "Continuity" in the strap they purchased.

One review mentions

WARNING FOR PURCHASERS AND ALL BRANDS OF A COMPUTER ANTI-STATIC WRIST STRAP – Before beginning my PC build, and looking at this $400 motherboard, from a past experience, I decided to verify that the Rosewill ESD Anti-Static wrist Strap will actually work, by testing it with my Multi meter. The Results were stunning - THERE IS NO CONTINUITY (CONNECTION) FROM THE ALLIGATOR CLIP TO THE METAL PAD ON THE WRIST STRAP – THIS NO STATIC PROTECTION!

So this brings a couple questions: 1) Is the bad connection just on the wrist strap I just bought, or on a whole bunch. 2) How many people buy any brand of anti-static wrist straps, put it on and think they are protected, then for their electrical part go bad thinking they were protected!!

Worse yet, most everything Nowadays is cheap China Stuff (CCS) and it is really hard for a company to make sure China/Asian products have quality.

I had randomly learned about continuity(right before reading this review), from a video of a water damaged iphone. The user used a multi-meter while connecting 1 side to something (couldn't see in the video), and would test both sides of the capacitor to see if it would beep. If both sides beeped, it seemed to be a bad capacitor, but if only one side beeped, that means it was good.

So I'm curious about,

  1. If the information presented in the video is true, and if so what exactly is going on there with the beeps and why it should only beep on one side?

  2. What exactly am I trying to test, and where, on the anti-static wrist band? The definition of continuity mentions "Continuous flow" so would I test the 2 ends, and multiple parts of the wire if something goes wrong, or...?

Any information about continuity testing, and any information about the subject in electronics, or some guidance to reading materials would be greatly appreciated, thanks.

EDIT: Review was from https://www.amazon.com/Rosewill-Anti-Static-Components-RTK-002-Yellow/product-reviews/B004N8ZQKY/ref=cm_cr_dp_synop?ie=UTF8&reviewerType=all_reviews&showViewpoints=0&sortBy=recent#R2LY6BRSK3A4UN

The segment is from 26 mins or so on this video https://www.youtube.com/watch?v=plmElKA6qKM&list=PLtjsWVbfWwk6cIQEN4aWjIiaP4VgXYuB0&index=3

Sorry share isn't working so I cannot get it directly at the timestamp.

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    \$\begingroup\$ Xaoling - Note: In future, if you quote from another website as part of your question (like you quoted a review), or ask about a video, please supply links to that information. I found the Amazon review that you quoted, but it's impossible to search for a video in the same way, of course. Although it doesn't apply to the wriststrap whose review you quoted, in case you are tempted, please note that "wireless" ESD straps do not work. \$\endgroup\$ – SamGibson Dec 22 '16 at 1:48
  • \$\begingroup\$ newegg.ca/Product/Product.aspx?Item=N82E16899261005 indeed many agree no continuity. Someone at the factory MAY HAVE cost reduced by replacing the black carbon thread with black nylon thread. (guess) No good. good to get a broad review base and this meets that critieria. You don't really NEED this. Just be careful and repeatedly ground yourself ( touch dissipative matte, case, power strip gnd if avail., whenever you move around. As W5V0 correctly said,. it should be 1M fixed R, but .1~10M is ok for current limiting ESD. \$\endgroup\$ – Sunnyskyguy EE75 Dec 22 '16 at 1:56
  • \$\begingroup\$ @SamGibson sorry, I updated the information, I thought I had posted the Amazon link though, but both links have been posted. \$\endgroup\$ – XaolingBao Dec 22 '16 at 2:11
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    \$\begingroup\$ The quality of "reviews" on Amazon is essentially zero. They REALLY are not worth the time it takes to read them. You can find well written reviews that seem intelligent and legitimate that are complete twaddle. DO NOT waste any more time reading Amazon reviews, at least of anything technical. If you measure something between 1M and 10M between the skin contact and the banana plug, then you are good. Lower resistance approaches danger and higher than 10M is of marginal performance. \$\endgroup\$ – Richard Crowley Dec 22 '16 at 3:04
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Overview:

A good wrist strap system has a large resistance between the skin contact and ground. Typically this is 1 MΩ, which is relatively large. This large resistance is there for your safety, in case an error somewhere connects you to a hazardous voltage. Even this high resistance is sufficient for protecting your devices from ESD.

A typical multimeter should be able to measure this resistance. However, most continuity tests will probably report it as open. This is because many continuity functions are looking for resistances less than 100 Ω.

Verifying your wrist strap:

Here is how you measure your wrist strap system - check from the skin contact side of the strap (red meter lead) to the part that gets connected directly to ground (black meter lead). Make sure your meter is configured to measure resistances higher than 1 MΩ, as the resistor will not be a precision tolerance. Note that in this picture I am making sure I don't touch any of the metal surfaces, which would give a bad reading.

Measure the resistance from the inside of the wrist strap to the outside or the end of the cord. Make sure you're on the high resistance scale of your meter if it does not auto range.

Properly Measuring a wrist strap system

In the labs I work in, the resistor is in the actual lead somewhere (the black wire). On the snap housing it is marked as 1 MΩ, and all the wrist straps are low resistance connections from the skin side to the snap connector. I have seen ESD straps with a 1 MΩ resistor built-in.

Don't use the continuity test:

For kicks and giggles, here's the result when you use the continuity check function on the whole thing - it reads as an open circuit (no continuity). With my setup, I would expect the meter to beep/show continuity on the wrist strap, but not on the wire lead.

Continuity won't work here

Conclusions:

Without knowing if the reviewer just used a continuity test, or actually measured the resistance (or even where they measured), it's impossible to draw any conclusions from the review. If the reviewer knew how to properly measure the system, then I would consider that a defective product. If the reviewer tried to use a continuity check across a 1 MΩ resistor, then the reviewer is not being helpful at all. The wording of the review makes me suspect the latter, but it is impossible to know from what was written.

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  • \$\begingroup\$ +1 - If the person quoted by the OP in that Amazon review really was (wrongly) expecting a continuity setting on their meter to be the correct test, then this previous question "Continuity Test on Resistor" is probably relevant too. \$\endgroup\$ – SamGibson Dec 22 '16 at 1:39
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    \$\begingroup\$ @sam absolutely. Without knowing the test performed or the skill/knowledge of the reviewer, that review is basically useless. \$\endgroup\$ – W5VO Dec 22 '16 at 1:47
  • \$\begingroup\$ @SamGibson I don't have a meter(yet), so I cannot really say much, but maybe this is a good opportunity to learn about what meter to purchase, since I have no clue what would be a good multimeter, but that might be a bit offtopic for this. From what you both are saying the reviewer is wrong, but you mention above the "proper" test I should be doing is testing for resistance of the band itself? We would set the resistance to a higher range when testing continuity, or is it a different test all together? Thanks a lot. \$\endgroup\$ – XaolingBao Dec 22 '16 at 2:14
  • \$\begingroup\$ @W5VO are there higher resistance bands for more industrial/professional work? I could imagine someone wanting to ground themselves with a very high resistance if they were working with big caps such as the ones that are found in power supplies which I hear are extremely dangerous. Also, where exactly would 'I test the strap? You said "skin contact and ground" so do we test the strap where it touches the skin, or multiple places? Thanks. \$\endgroup\$ – XaolingBao Dec 22 '16 at 2:20
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    \$\begingroup\$ @XaolingBao I added some pictures to help explain what's going on. \$\endgroup\$ – W5VO Dec 22 '16 at 16:12
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The built-in resistor might be well above 10M ohms, and a cheap DMM meter would see this as an open circuit.

Wrist straps are not supposed to short your body directly to ground. Doing so creates an electrocution hazard, especially if you accidentally bump against live AC connections with your other hand, the one lacking the wrist strap. (This would direct the line-power current-path through your chest and out your grounded wrist.)

To avoid the danger, wrist straps must contain a built-in resistor in the Megohm range. Their purpose after all isn't to make you touch a questionable power-tool while standing barefoot in grounded salt water. Instead, the goal is to remove any DC body-voltage by draining you of (perhaps kilovolts worth!) any surface-charge.

To perform this task, which max value of series resistance is appropriate? The resistor must significantly discharge your personal capacitance in roughly one second. 0.1sec might be better, so let's use that value. A human body has approximately 100pF capacitance to ground. But worse-case, you might be lying on a concrete floor with grounded steel inside it. This produces a body-capacitor to Earth having a much higher value. Let's say that max human capacitance is 3x higher: 300pF.

The crude time-constant calculation is simple: T(sec) = R(ohms) x C(farads). Or, R=T/C. So, R = 0.1sec / 300x10^12F = 3Megohms max. A much larger resistance would still work fine, but any kilovoltage built up on your body would drain in a few seconds, rather than semi-instantly.

Also, what's the minimum appropriate resistance? If you poke your finger into 120VAC, you REALLY REALLY want any resulting current to stay well below 1mA. Let's say 0.1mA for a fairly safe value of through-chest current. And, lets say 240VAC for the line-voltage hazard. By Ohm's law this gives a wrist-strap series resistor value of R = V/I = 240V/.0001A = 2.4 Megohms min.

Various manufacturers may err on the side of caution, and their wrist strap resistor may be closer to 20M than to 2M. If so, a typical DMM would see it as an open circuit. Yet your high-volt body-charge sees the same resistor as nearly a short circuit. "Frictional" electrostatics is weird that way: typical supply impedances are above 1M, and can be up in the giga-ohms. A normal voltmeter cannot measure human body voltages without applying their "short circuit" of 10Megs. To deal with such HV measurements, your voltmeter needs a Zin of 10G-ohms or higher, not the typical 10M-ohms.

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  • \$\begingroup\$ Thanks for the information. So what exactly is the point to grounding yourself via the alligator clip if we are just wanting to resist the charge via the wristband? Is the grounding part of it? I gues I'm confused by your comment about "shorting to ground." Interesting comment about the wrist band. So essentially the current flows to the grounding point. From what you're saying I would want a higher Megaohm resistance in my band then? Can you explain about the grounded steel and needing 3x higher capacitance? Thanks. \$\endgroup\$ – XaolingBao Dec 22 '16 at 2:34
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    \$\begingroup\$ @XaolingBao When we cross a carpet on low-humidity days, we charge up our body-capacitance, and then produce ESD if we touch any piece of equipment. Typical body voltages: 1KV for tiny sparks, 8KV for loud painful sparks. But even body-voltage less than 1KV can harm electronics. So, we want to "ground" ourselves in order to drain our charge and lower our body-voltage to ~zero. An alligator clip and metal strap would do this, but then a grounded human is in danger of 120VAC shocks. With a resistor, the strap still drains charge, and the human won't be harmed if they touch "hot" AC terminals. \$\endgroup\$ – wbeaty Dec 22 '16 at 2:47
  • \$\begingroup\$ @XaolingBao If you lie down upon the floor, your body capacitance to Earth is larger. In that case, the series-resistor in the wrist-strap would need to be smaller value, in order to still remove your body net-charge within one second. I calculate: 10M ohms may work fine if you're sitting on an insulating chair. But if you lay on the floor while pulling cards from your PC, while sliding your legs along your nylon carpet, or crawling around while wearing wool pants ...then maybe the minimum ohms in the wrist strap should be 3M, not ten or twenty megohms. \$\endgroup\$ – wbeaty Dec 22 '16 at 2:51
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Short Answer: the consensus is measurement error. Strap is OK, so Trust, but Verify. ( Test Engineer's creed. )

https://www.amazon.com/product-reviews/B004N8ZQKY/ref=acr_dpx_hist_5?ie=UTF8&filterByStar=five_star&reviewerType=avp_only_reviews&showViewpoints=0

At least one reviewer correctly measures leakage resistance at 1002 Kohm

The others must have been using continuity which measures voltage drop with 10uA or 100uA which is overscale and actually reads in Volts on a xxxx scale using my Fluke75, intended for Vf diode drop . I get 2.095V max on my tongue which also measures at 0.4M so it is just our of range for EOS straps ( the proper name ) This means continuity applies a constant current ( AC) of 2V/0.4M= 20uA roughly

If you only had a continuity meter scale ( like mine, not all the same uA) it can still be measured with a 500K then strap in parallel drops 33% or 100K and 1M strap drops roughly 9%

1M is the defacto std for Wrist , heal, toe and matt straps. Matts are measured in Ohms per square of any size around 10e10 to 10e11, no more and no less.

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If you don't own a wrist strap you can still hook an alligator clip to your pinky and the other side to chassis ground. Disconnect if pinky shows discoloration.

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