Antistatic wrist strap

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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. 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 an elastic 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. 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 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.
Wrist straps designed for industrial use usually connect to Earth Bonding Points, ground connections
built into the workplace, via either a standard 4 mm plug or 10 mm press stud, whereas straps
designed for consumer use often have a crocodile clip for the ground connection.
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. They are used particularly
in an operating theatre, where oxygen or explosive anesthetic gasses are used.
“Wireless” or “dissipative” wrist straps are available, which claim to protect against
ESD without needing a ground wire, typically by air ionization or corona discharge. These
are widely regarded as ineffective, if not fraudulent, and examples have been tested
and shown not to work. Professional ESD standards all require wired wrist straps. See also Antistatic device
Antistatic bag Antistatic garments
Antistatic agent Antistatic mat Electrostatic sensitive device

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