In ANSI/ESD S20.20 Section 8.2 (Personnel Grounding), recommended requirements are outlined for how personnel should be electrically connected to a grounding system with a wrist strap. S20.20 also includes recommendations for “ESD Control items” (i.e., esd mats and wrist straps) in Section 8.3 ESD Protected Areas (EPAs).
What is Static Control? Practical Considerations
Mats bond work surfaces. Wrist straps bond people. Static-shielding ESD smocks reduce charge buildup on clothing and help prevent the body from coupling charge to nearby devices. Ionizers generate positive and negative ions that neutralize charge, especially on insulators that can’t be reliably grounded.
In S20.20, recommendations for insulators are covered in Section 8.3.1 Insulators. For our purposes, treat any ungrounded object as a potential ESD source. These include familiar sources of static (carpets, plastics, unfinished wood) and isolated conductors (covered in Section 8.3.2).
Clothing can also be a source, too: movement and friction can generate static electricity, and that charge can couple into sensitive electronics even before you touch them.
The reliable ways to control charge in the work area are to remove high-charging insulators, cover work surfaces with grounded dissipative materials, use ionization to neutralize charge on exposed surfaces, and wear static control garments to reduce charge generation and “shield” what you’re wearing. That’s why many engineers combine grounding, shielding, and ionization in an ESD workstation setup.
When using an ESD mat and wrist strap, consider your entire work area, your clothing, and how you are grounding yourself.
ESD Mats for Tables
ESD mats that are compliant with S20.20 are defined in Table 3 of Section 8.3 ESD Protected Areas (EPAs). This table in turn references the Product Qualification (STM 4.1) and Compliance Verification (TR53) standards for on-site use.
• Anything less than 1 x 106 ohms (a Megohm) is considered Conductive.
•Anything above 1×109 ohms (a Gigaohm) is considered Insulative.
• Anything between these two points is considered Static Dissipative.
The ESD Association recommends in ANSI/ESD S4.1 that ESD mats be static dissipative when used as work surfaces, such as shelves, tables, trays, and workbenches, where they provide a controlled path to ground for items and tools. While ESD programs can be tailored to specific needs, these ranges represent consensus.
As shown in the picture, most ESD mats used for these purposes are static dissipative on top (blue) and conductive on the bottom (black). The conductive bottom layer ensures charge flows to ground if the mat contacts a grounded surface.
ESD Ground Points
ESD Ground Points come in several different types. The grounding cable connects the anti static mat used as a work surface to the grounded electrical outlet.
There are grounding cables for mats, wrist straps, and common point grounds for both.
Do not use the alligator clip to attach the wrist strap to the anti static mat. This will not work. In fact, this will increase the total system resistance to ground because the wrist strap and mat ground cords incorporate built-in resistors.
Unless necessary, it’s recommended not to use the alligator clip. While it seems convenient, it is best used only when you are sure of the pathway to the ground.
ESD Wrist Straps and Mats
A wrist strap keeps the wearer at the same electrical potential as the mat and the common point ground by providing a controlled path to ground. Instead of allowing static charge to build up on the body, the strap continuously equalizes charge as you move, reducing the chance of a sudden discharge into sensitive electronics.
Many wrist straps use conductive fibers (often silver- or carbon-based) woven into a fabric band to ensure reliable contact with the skin. When connected through the cord, this contact allows any accumulated charge to dissipate gradually rather than releasing all at once.
When both the wrist strap and the work surface are connected to a common ground point, the person and the mat share the same reference. That minimizes voltage differences between you, the work surface, and the device—helping prevent electrostatic discharge during handling.
In ANSI/ESD S20.20 Section 8.2 (Personnel Grounding), wrist straps are recommended to be used at all times if personnel are seated at workstations. When standing, it recommends that personnel be grounded via a wrist strap and/or a footwear/flooring system. If a wrist strap is worn with a static control garment for grounding, it should meet the requirements of a groundable static control garment system.