0
\$\begingroup\$

Anti-static wrist straps come in 2 flavours: fabric strap or metal band. A metal band is more expensive, but is it better? Or is it just for cleanrooms?

  • The fabric strap is attached to a little metal piece which makes contact to your skin to conduct static electricity away. The fabric strap itself often has a surface resistance of +/-1E5 ohm on the inside and +/-1E12 ohm on the outside.
  • The metal band makes contact around your whole wrist, because it's made of stainless steel all the way around. It's very conductive on the inside, but the outside is often painted.

Is there any change of static build up on the insulating outside of a stainless steel anti-static wrist band?

|improve this question
\$\endgroup\$
  • \$\begingroup\$ Antistatic straps should have a resistance if about 1E6 Ohm to ground (uually using a resistor on the wire) to revent user electric shock if they touch mains etc potential objects. Doing this while hard grounded is a very bad idea. So 1E5 in strap proper is irrelevant. \$\endgroup\$ – Russell McMahon Oct 26 '16 at 10:50
  • \$\begingroup\$ The 1E6 ohm resistor you're talking about is between the (very conductive) metal part of the wrist strap and the grounding wire. The fabric strap itself (attached to the metal part) often has a surface resistance of +/-1E5 ohm on the inside and +/-1E12 ohm on the outside. \$\endgroup\$ – Marty Oct 26 '16 at 10:54
  • \$\begingroup\$ Yes. The extra 1E5 in the discharge path is 10% of the resistor to ground. So if calue were exact you'd get 1.1 megohm. 1.1 = 1 here :-). \$\endgroup\$ – Russell McMahon Oct 26 '16 at 11:00
  • \$\begingroup\$ The metal ones probably last longer. Fabric ones loose their stretch. \$\endgroup\$ – Sean Houlihane Oct 26 '16 at 11:24
5
\$\begingroup\$

The point about static electricity is that there's usually not that much energy, i.e. charge, building up over a short time.

Therefore, a couple kOhms resistance don't make that much difference - your body voltage would break down over that.

I'd argue that the fabric ones are better for most usage scenarios: they are simply more comfortable to wear, and that makes a difference in usage, and also, humans become sloppy over time – and that'll lead to you being more likely to take off the wristband "earlier".

Is there any change of static build up on the insulating outside of a stainless steel anti-static wrist band?

I'd say: no. Not at all. Ok, it depends on the conductivity and thickness of that lacquer, but assume the following. I'll try to draw a worst case scenario.

You take your angora bunny to your workplace.

Wikimedia Commons: English Angora

For some reason, that bunny gets aggressive/bitey when you don't pet with your wrist, so you pet it with your wristband, and by doing so, you're constantly stroking with the outside of your wristband.

Charge builds up on the wristband's outside. However, that charge is either very small, or directly discharges into the metal part.

So you're fine.

Someone notices you and your pet rabbit at work and fires you, but not without offering the position of chief rabbit safety overthinker in his night-time job, organizing rabbit fairs. You become famous and rich.

Not that bad for a worst-case scenario.

|improve this answer
\$\endgroup\$
  • \$\begingroup\$ A German with a sense of humor! Now I have seen it all ;-) \$\endgroup\$ – winny Oct 26 '16 at 10:23
  • \$\begingroup\$ Haha! :-) The lacquer on the outside can provide at least 5kV volt insulation, according to some manufacturers. So rubbing the outside of a metal wrist band over my angora bunny should, in theory, lead to static build up on the outside. Will this static electricity flow away through the lacquer at all? \$\endgroup\$ – Marty Oct 26 '16 at 10:36
  • 2
    \$\begingroup\$ @winny, you should come to Germany :) we've all sorts of humor, highly engineered, as soon as you've got your humor permit, which of course involves a lot of correctly processed application forms! (also, we've got traumatized bunnies with compulsive biting, so better bring sturdy boots) \$\endgroup\$ – Marcus Müller Oct 26 '16 at 10:49
  • 1
    \$\begingroup\$ @RussellMcMahon German humor licenses are practically irrevocable; in theory, you just have to fill a few permit-challenge forms, get them signed by an accredited humor evaluation facility, and then hand them in and wait for them to be processed, then show up in person for the humor-permit-revocation process hearing, but in practice, the ministry that assigns humor evaluation accredition permits is so overloaded that there's not a single institution out there that can accredit humor evaluators, and hence, the two existing evaluators have crazy pricing. \$\endgroup\$ – Marcus Müller Oct 26 '16 at 11:22
  • 1
    \$\begingroup\$ Optional: a. All or lead intone "we will exterminate you. Exterminate. Exterminate. Exterrrrminate ... or (b.) "We Pentium. of Borg. Division is futile. You will be approximated ... \$\endgroup\$ – Russell McMahon Oct 26 '16 at 13:03

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.