Antistatic wrist strap
An antistatic wrist strap, ESD wrist strap, or ground bracelet is an antistatic device used to safely ground a person working on very sensitive electronic equipment, to prevent the buildup of static electricity on their body, which can result in electrostatic discharge (ESD). It is used in the electronics industry by workers working on electronic devices which can be damaged by ESD, and also sometimes by people working around explosives, to prevent electric sparks which could set off an explosion. It consists of a stretchy band of fabric with fine conductive fibers woven into it, attached to a wire with a clip on the end to connect it to a ground conductor. The fibers are usually made of carbon or carbon-filled rubber, and the strap is bound with a stainless steel clasp or plate. They are usually used in conjunction with an antistatic mat on the workbench, or a special static-dissipating plastic laminate on the workbench surface.
The wrist strap is usually worn on the nondominant hand (the left wrist for a right-handed person). It is connected to ground through a coiled retractable cable and 1 megohm resistor, which allows high-voltage charges to leak through but prevents a shock hazard when working with low-voltage parts. Where higher voltages are present, extra resistance (0.75 megohm per 250 V) is added in the path to ground to protect the wearer from excessive currents; this typically takes the form of a 4 megohm resistor in the coiled cable (or, more usually, a 2 megohm resistor at each end).
Wrist straps in industry usually connect to Earth Bonding Points (part of the grounding system) via either a 4 mm plug or 10 mm press stud, whereas personally owned straps are likely to be connected to ground via a crocodile clip.
In addition to wrist straps, ankle and heel straps are used in industry to bleed away accumulated charge from a body. These devices are usually not tethered to earth ground, but instead incorporate high resistance in their construction, and work by dissipating electrical charge to special floor tiles. Such straps are used when workers need to be mobile in a work area and a grounding cable would get in the way, such as in an operating theatre.
Wireless or Dissipative wrist straps are available, but they are widely considered as pseudoscientific hoax products. The claims of the operating principles vary from "Ion Neutralization, Skin Effect, Point Discharge and Corona Discharge Effect" to "Selglard electric halo principles".[1][2]
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Disposable ground straps used during installation of computer equipment
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[edit] See also
[edit] References
- ^ "We Challenge Wireless Wrist Strap Manufacturers". ESD Journal. 2005-10-27. http://www.esdjournal.com/techpapr/sfowler/wireless.htm. Retrieved 2010-03-31.
- ^ "ESD Systems FAQ". Esdsystems.com. http://www.esdsystems.com/QuestionsAndAnswers/ShowQuestion.aspx?i=17. Retrieved 2010-03-31.
