Desco 19350 Technical Bulletin

Wrist Straps
Grounding, Testing and Maintenance
Wrist Straps per ANSI/ESD S20.20
"All personnel shall be bonded or electrically connected to
the grounding / equipotential bonding system when handling
ESDS [ESD sensitive] items." "When personnel are seated
at ESD protective workstations, they shall be connected to
the grounding/equipotential bonding system via a wrist strap
system." [ANSI/ESDS20.20-2007 sections 8.1 and 8.2]
Location of Wrist Strap Ground Point
Wrist straps, ESD worksurfaces, and floor mats are to be
grounded to remove electrostatic charges connected to a
common point ground. The common point ground should
be connected with one ground cord to the "green wire"
equipment ground.
COMMON POINT
GROUND #09826
Figure 1. Common point ground for each workstation
This may be accomplished in a variety of ways utilizing a
common point ground block, a ground bus, or connecting
directly to the nearest AC "green wire" equipment ground
point. In a properly wired building, the nearest reliable
equipment ground point will be ground or the center screw of
the standard 110 VAC electrical outlet.
Each ESD workstation must be individually grounded to the
ground bus or "green wire" equipment ground. Do not wire
worksurfaces or other ESD devices in series or "daisychain"
them. This can create unknown higher resistance to ground.
For a more detailed discussion of ESD grounding see Desco
technical bulletin TB-2007. For instructions on grounding
Desco worksurface mats see technical bulletin TB-2000.
Figure 2. "Green wire" equipment ground
March 2014
TB-2005 Page 1 of 3
TECHNICAL BULLETIN TB-2005
BENCH MAT
WRIST STRAP
WITH COIL CORD
FLOOR MAT
GROUND #09814
FLOOR MAT
WARNING!
DO NOT
DAISY CHAIN
GREEN
THE WRIST STRAP!
WIRE
EQUIPMENT
GROUND
NO
DESCO WEST - 3651 Walnut Avenue, Chino, CA 91710 • (909) 627-8178
DESCO EAST - One Colgate Way, Canton, MA 02021-1407 • (781) 821-8370 • Website:
Test The Ground Before You Use It And Periodically
Thereafter
Do not assume that any AC electrical outlet is properly
wired. Even if it was originally wired correctly it can become
ungrounded due to corrosion and wear. Test the ground you
intend to use before you hook up. We suggest using Desco's
item 98132 AC Outlet Analyzer and Wrist Strap Tester.
A Banana Jack Is Recommended
Almost all wrist strap manufacturers terminate wrist ground
cords with banana plugs. This is because the banana plug
and jack have proven to be a fast and reliable way to attach
to ground. If you must use another method such as snaps or
alligator clips, due to your particular environment, be sure to
test the connections often.
Note: Many wrist strap users clip the wrist cord to the edge
of an ESD mat. This process is not recommended as it can
increase the total system resistance to ground to over the
35 megohm required limit of ANSI/ESD S20.20. "Wrist strap
ground cords must be connected to a groundable point or an
equipotential bonding point. Do not connect to a snap on a
dissipative mat unless it is the groundable point for the mat.
Do not clip a wrist strap to the edge of a dissipative mat."
[ESD Handbook TR20.20 section 5.3.2.7] Best industry
practice is that ESD Ground Connections should be firm
fitting connecting devices such as metallic crimps, snaps
and banana plugs shall be connected to designated ground
points. Use of alligator clips is not recommended.
Figure 3. Desco's 09740 / 09741
09835 / 09836 quad common point ground cord are two easy
ways to provide multiple banana jacks at any workstation.
Compliance Verification of the Ground System
Set up a schedule to be sure that all ESD grounds are
inspected and tested periodically, every six months for
example.
Testing the Wrist Strap
The best test of the wrist strap system is while it is worn. This
includes all three components: the wrist band, the ground
cord (including current limiting resistor), and the interface
with the wearer's skin.
Made in the
United States of America
09835/09836
09740
dual bench mount and
Desco.com
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