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The resistance of my Belkin anti-static wrist strap shows 0.983, but how do I know that I am grounded by attaching it to computer power supply alone? See the picture below.

enter image description here

How do I know if that resistance is absorbed by the grounded contact? Must I touch a metal plate below the strap with one lead and power supply with another lead?

UPDATE: I wanted to know if there is a contact between wrist strap and power cable's grounded contact through power supply. Since wrist strap works, i wanted also to know that grounding it to power supply and then connecting to power outlet will work as well so i touched wrist strap's metal plate with one lead and grounding contact of power cable with another lead and saw same resistance as mentioned above. This means that everything works.

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  • \$\begingroup\$ Please describe what you are trying to accomplish. It is hard to find out what you really mean, so I posted general advice on using a wrist strap. \$\endgroup\$ – posipiet Sep 9 '11 at 13:32
  • \$\begingroup\$ Since you're expressing concerns about ESD, may I point out that that interesting polyethylene work surface may present some issues, as well. \$\endgroup\$ – JustJeff Sep 10 '11 at 0:57
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A proper ground strap connection should show 1 to 10 megohms between the part that contacts your skin and the ground terminal of the power cord. This resistance is there to prevent electrocution through the strap.

The point of a ground strap is to dissipate static charge. A large resistor does this slowly enough to not "zap" you, but also doesn't turn you into a large ground rail yourself.

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  1. Your wrist straps clamp should only ever be attached to ground (also called earth) on the wall plug. Nowhere else except a special grounded spot which exists in some lab setups. It must never ever be attached to any cable coming out of the power supply. If you are not perfectly positively sure your grounding is safe, you are better off not using a wrist strap.
  2. The wrist strap is there to protect your equipment from you. Not the other way round. It is meant to dissipate static electricity on your person to ground, so you dont harm any sensitive electronics components. A computer power supply is not a sensitive component.
  3. The wrist strap is not there for your safety.
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  • \$\begingroup\$ Weller soldering stations have a 3.5mm socket specifically for grounding. cooperhandtools.com/europe/spare_parts/weller/index1.htm \$\endgroup\$ – starblue Sep 9 '11 at 15:21
  • \$\begingroup\$ If you're not working on anything too sensitive or expensive, you can attach the wrist strap to a large ungrounded hunk of metal, like the leg of a workbench. Static will dissipate quickly to the bench and slowly from there to the air. You wouldn't build a factory assembly line like that, but for some purposes it can be good enough. \$\endgroup\$ – Matt B. Sep 10 '11 at 1:47
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I presume the 0.983 resistance is 0.983M\$\Omega\$. Like posipiet says, the grounding is there to protect ESD-sensitive electronics from electrostatic charge you carry. On a dry winter day this can easily run to several kV. One those days I almost always get a discharge when I get out of my car and touch the garage door's handle. A 2cm spark is not uncommon. Think of what damage charges like these could do to CMOS circuits.
The connection from the antistatic wrist strap to the ground is usually rather high resistance, typically 1M\$\Omega\$. That's low enough to let any charge leak away, and at the same time high enough to prevent connecting become a shocking experience in case you would be charged to kilovolts.

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Most places I have worked have a wrist strap tester. Either you check daily or it is built into the socket at the bench.

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  • 2
    \$\begingroup\$ Can you tell us how such a tester works? \$\endgroup\$ – Federico Russo Sep 10 '11 at 12:18
  • \$\begingroup\$ @FedericoRusso it would seem to give you charge to simulate static, and then to test for that charge on the return route of the band. Just going off the picture which clearly has an electro-conductive plate the user is pressing and a place to plugin the wrist strap: grainger.com/product/3M-Tester-6NV88?s_pp=false&picUrl=//… \$\endgroup\$ – Evan Carroll Jan 4 '16 at 21:22

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