ESD Wrist Straps for ESD Control
ESD Wrist Straps are the most common personal grounding device used in the Electrostatic Discharge Control or ESD Control industry. Why use a Wrist Strap? Since ungrounded people are often the biggest cause of ESD damage, wrist straps are the first line of defense in ESD control. Seated operators must wear wrist straps. All operators that handle un-packaged ESD sensitive items must be grounded.
"All personnel shall be bonded or electrically connected to ground or contrived ground when handling ESD sensitive items. When personnel are seated at ESD protective workstations, they shall be connected to the common point via a wrist strap system." [ANSI/ESD S20.20 section 6.2.2.1 Personnel Grounding Requirement]
The purpose of a wrist strap is to provide a groundable path for charges that are generated by workers in a static control or ESD protective area or field service. A wrist strap is made up of two components including a wrist band and a coiled cord. The way a wrist strap works is that a conductive surface on the inside of the wrist band makes contact with the operator’s wrist. The band’s buckle is outfitted with a snap for a coiled ground cord. The coil cord has a “banana” plug which is to be plugged into a ground cord or monitor jack. There are two basic technologies for wrist straps: single-wire wrist straps and dual- wire wrist straps (also referred to as dual-conductor wrist straps). Single-wire wrist straps are the most common type. They consist of a single conductor and have a banana type jack. They can be plugged directly into a ground cord or may be used with a single-wire continuous monitor. Dual-wire wrist straps have two conductor wires and have a mono type jack. They are used exclusively with dual-wire continuous wrist strap monitors. Both technologies are equally effective at discharging static electricity from the operator.
The most common type of wrist straps come with an elastic wrist band constructed from elastic knitted clothe material with conductive fibers woven in. Other types include metal wrist straps.
Wrist Strap Testing
Wrist straps require regular testing to ensure that the operator is grounded properly. There are two basic type of wrist strap testing: on-demand or periodic wrist strap testers and continuous wrist strap monitoring. If not utilizing Continuous Monitors the Wrist Strap should be tested daily while being worn by the operator.
“The wrist strap system should be tested daily to ensure proper electrical value. Nominally, the upper resistance reading should be <10 Megohms or a user defined value.” [ESD-S1.1 section 6.1.3 Frequency of Functional Testing] “Proper testing of the wrist strap includes the resistance of the groundable point on the end of the cord, the cord itself, the resistor, the cord-to-cuff snap connector, the resistance of the interface of the cuff, the cuff/wrist interface, and the resistance of the person between the wrist and the hand that contacts the test electrode.” [ESD Handbook TR 20.20 section 5.3.2.4.2 Additional User Wrist Strap Testing] “A log should be maintained which verifies that personnel have tested their personal grounding devices.” [ANSI/ESD S20.20 section 6.2.2.2 Personnel Grounding Guidance]
If the wrist strap fails a test dry skin could be the culprit. A special dissipative lotion is recommended. Disposable wrist straps are used for visitors in the static control area or can be kitted with ESD Sensitive Devices (ESDSD) for field installation. The most common application for wrist straps are where the operator is stationary working in a fixed location where the wrist strap can be grounded through its coiled cord. Most wrist straps are usually used in conjunction with a dissipative mat or work surface laminate. If worker mobility is required in the static control area, operators can be grounded through the use of ESD footwear.
Wrist straps MUST have a ground system to effectively dissipate charges. While there are claims by some offering a wireless wrist strap, cordless wrist strap, or wireless ESD straps these are not effective grounding devices. Learn more.
While “wrist strap” is the proper term for these devices, they are sometimes referred to as antistatic wrist straps, anti static wristbands, static wrist straps, wrist grounding strap, or static strap.
To learn more about wrist straps see the article “Wrist Straps and ESD Control” by Mark Hempel – DII Wrist Strap Product Manager, and Gene Felder – DII Corporate Product Manager
To learn more about wrist straps, visit our Q&A library. Ask a question here.
Click HERE for a Selection Chart on ESD Wrist Straps.