Desco TB-2000 Installation Manual

TB-2000 January 2009 Page 1 of 4

Inst allation and Maintenance
of ESD Protective Work Surfaces

Foreword

To enhance your understanding of this technical bulletin we
recommend that you read the following EOS/ESD Standards:

ANSI/ESD S20.20 - Development of an Electrostatic

Discharge Control Program
ESD ADV 1.0 - Glossary of Terms
ESD S4.1 - Work Surfaces
ESD S6.1 - Grounding
ANSI ESD S11.11 - Surface Resistivity

These documents can be obtained directly from the ESD
Association, 7902 Turin Rd., Building 3, Suite 2, Rome, NY 13440­2069, [phone], www.esda.org.

Introduction

The purpose of an ESD protective work surface is to aid in the
prevention of damage to ESD sensitive components and
assemblies from electrostatic discharge. An ESD protective work
surface provides protection in the following two ways:

1. Providing an antistatic work surface area that will not allow
static electricity to be generated at potentially hazardous levels.

2. Removing the charge from a conductive object placed on the
work surface.

ESD protective work surfaces are catagorized into two general
categories: conductive and dissipative.

A conductive work surface is defined by most documents as a
material that has a surface resistivity of less than 1x10

5

ohms/square. Conductive materials are the quickest to ground a
charge, but they can also cause damage by discharging too
rapidly. Conductive materials are usually used as floormats or
flooring products.

A dissipative work surface is defined as being materials having a
surface resistivity of at least 1x10

5

, but less than 1x10

12

ohms/square. Dissipative materials minimize the generation of
static charges, and will dissipate a charge slow enough so that a
spark will not occur. Dissipative materials are usually the preferred
choice for bench top work surfaces.

General Guidelines

1. ANSI/ESD S20.20 requires that all conductors, including

personnel, must be electrically connected and attached to a
known ground.

2. For proper and safe grounding the ESD ground must be

tied directly to and at the same potential as the building or
“green wire” ground.

3. Per ANSI/ESD S20.20, the ESD control program can in no way

replace or supercede and requirements for personnel safety.
Ground fault circuit interrupters (GFCI) and other safety
protection should be considered wherever personnel might
come into contact with electrical sources.

4. All electrical circuits at an ESD protected workstation, especially

those used as the tie-in point to the utility ground, should be
verified for proper wiring configuration, ground impedance and
GFCI function when the station is installed and periodically
thereafter.

5. The selection of ground cords is intimately related to the
material selected for an ESD protected work area, personnel
safety, and the products’ relationship to the organization’s
material handling procedures. It is important for a user to be
familiar with their oganization’s grounding specifications and
ESD control procedures prior to selecting ground cords.

Common Point Grounds

A common point ground is defined by the EOS/ESD-S6.1,
“Recommended Grounding Practices” as:

1. A grounded device where two or more conductors are bonded.

2. A system or method for connecting two or more grounding

conductors to the same electrical potential.

Examples of conventional common point grounds and other
ground cords are illustrated below.

09835

09740

09817

09814

Figure 2. Other ground cords.

Common point grounds are designed to provide earth ground for
table mats and wrist straps. NOTE: DO NOT DAISY CHAIN.
Because of the high resistances inherent to many types of
protective surfaces, daisy chaining of these materials can severely
limit their ability to properly dissipate and protect against static
charges.

Figure 1. Typical common point grounds.

DESCO WEST - 3651 Walnut Avenue, Chino, CA 91710 • [phone] • Fax [phone]

DESCO EAST - One Colgate Way, Canton, MA 02021-1407 • [phone] • Fax [phone] • Web Site: http://www.desco.com

TECHNICAL BULLETIN TB-2000

Made in America

© 2009 DESCO INDUSTRIES INC.

Employee Owned

09837

09825

COMMON POINT GROUND

Per ANSI/EOS/ESD S6.1, Grounding paragraph 4.1.1 "Every
element to be grounded at an ESD protected station shall be
connected to the same common point ground."

ESD Handbook TR 20.20 paragraph 5.1.3 Basic Grounding
Requirements "The first step in ensuring that everything in an EPA
is at the same electrical potential is to ground all conductive
components of the work area (worksurfaces, people, equipment,
etc.) to the same electrical ground point. This point is called the
common point ground. The next step in completing the ground
circuit is to connect the common point ground to the equipment
ground (third wire, green)."

TB-2000 Page 2 of 4

Grounding Methods

Method 1 (Grounding via ground cords)

1. Desco recommends using a common point ground cord when
grounding via ground cords. Most common point ground cords
will ground your ESD protective work surface and provide
banana jacks for two wrist strap grounds.

2. A common point ground should be installed at each workstation
and should be connected directly to a verified utility “green
wire” ground or to a verified grounding bus which is connected
to the utility ground. Only one groundable point should exist on
a work surface.

Figure 4. Common point ground for each workstation.

3. Wrist straps should never be grounded through a work surface,

as the added resistance of the work surface material will
prevent the wrist strap from operating properly.

WRONG! RIGHT!

Figure 5. Proper grounding of wrist straps.

4. A current limiting resistor in the wrist strap ground cord is

recommended. The EOS/ESD Standard S-1 calls for this to be
a one megohm resistor.

Method 2 (Grounding via a grounded conductive surface)

1. This alternate form of grounding should only be employed

when using a homogeneous dissipative material with a volume
resistivity of less than 108ohms/centimeter.

2. The dissipative or conductive work surface may be placed on a

properly grounded laminate, metal or other conductive surface.
The worksurface will electrically couple to teh grounded
surface and may not require separate grounding.

Figure 6. Alternate grounding method

For additional information on grounding we recommend Desco
Technical Bulletin TB-2007.

Groundable Point Installation

1. Before installing a groundable point on your work surface you
must first determine whether you will need a snap socket or
stud, the type of snap hardware and the location.

Figure 7. Three kinds of snaps.

2. Desco has three types of 10mm (.395") field installable mat
grounding snaps. The first type is a screw-on snap kit designed
for use on homogeneous mats, but it can also be used on two­layer work surfaces without ill effect. This is Desco item number

09864.
A. Determine the position of the grounding snap (one only

per mat) and type of fastener you will be installing (socket or
stud). Punch a hole through the material with a small phillips
screwdriver or awl.

B. Remove the release paper from the circular label and

affix it so that it aligns with the hole on the material.

C. Select one of the screws as follows:

Material less than .100" thick - short screw
Material greater than .100" thick - long screw

D. Insert the screw through the top on the snap fastener, the

washer, the label and the material. Affix the assembly with
the conical nut supplied with the kit and tighten down the
screws.

DESCO WEST - 3651 Walnut Avenue, Chino, CA 91710 • [phone] • Fax [phone]

DESCO EAST - One Colgate Way, Canton, MA 02021-1407 • [phone] • Fax [phone] • Web Site: http://www.desco.com

WRONG!

RIGHT

Figure 3. ESD work surfaces should never be grounded in series,
i.e. daisy chained.

3. When using this type of grounding method be sure to test that
the worksurface is properly grounded.

© 2009 DESCO INDUSTRIES INC.

Employee Owned