standards and guidelines for communication sites - Radio And ...

APPENDIX
C
PROTECTING AGAINST ELECTROSTATIC
DISCHARGE IN EQUIPMENT ROOMS AND DISPATCH
CENTERS C
C.1 BACKGROUND INFORMATION
Static electricity is defined as an electrical charge that is caused by an imbalance of electrons on
the surface of a material. This imbalance of electrons produces an electric field that can
influence other objects at a distance. Electrostatic Discharge (ESD) is defined as the transfer of
electrical charge between bodies at different electrical potentials.
ESD can severely affect the performance and reliability of electronic equipment. ESD failures
may occur at a site and not immediately be detected because voltage levels that can cause
component failure are below the perception threshold of the individual. (IEEE STD 1100-1999,
section 6.4.3.3)
Electrostatic charges are built up on the human body by triboelectric charging. Triboelectric
charging takes place when two materials come in contact and are separated and a transfer of
positive or negative ions takes place. Just by walking across an unprotected floor when the
humidity level is low, a person can create a triboelectric charge buildup in the range of 25,000
volts and up. Cathode-ray tube video terminals can also generate intense electric fields that can
transfer high amounts of electrostatic charges on the human body. Normally, discharges from the
hand are usually imperceptible below potentials of 3000 volts; for sensitive areas such as the
face, the threshold of perception may be 500 volts or lower (ANSI T1.321-R2000, section 4).
Electrostatic buildup and discharge in a dispatch room can be very annoying to the operator
especially when the high voltage energy discharges through the operator's headset ear piece. The
high voltage discharge can not only cause annoyance and pain due to the high voltage heat
transfer, it can also cause data and audio signal corruption as well as damage or destroy
equipment.
C.2 EQUIPMENT HANDLING AND STORAGE
To reduce ESD damage to electronic equipment, wrist straps connected to ground should be
worn when handling static sensitive devices. Static-dissipative work surfaces and grounded
dissipative (or conductive) floor surfaces should be used in equipment rooms. Storage areas
should contain grounded cabinets on grounded permanently static-dissipative shelves. Ground
points for wrist straps should be provided at strategic locations near equipment sensitive to
electrostatic discharge. (ANSI T1.334-2002, section 12)
68P81089E50-B 9/1/05 C-1