A Word about ESD (Electrostatic Discharge)
A Word about ESD (Electrostatic Discharge)
What Is It? Static electricity is a result of triboelectric charging of two dissimilar nonconductive mater-
ials that are rubbed together, such as rubbing your feet on a carpet on a cold winter day or in a dry cli-
mate. The resulting charge is detected when you reach out to touch a doorknob or some other metallic
object. The resulting discharge may only be startling or, in severe cases, it may even be painful. The
actual electrical charge is dependent on the materials being rubbed together, humidity, the rate of sep-
aration, and other factors.
What Can It Do? While this effect may be disturbing to humans, the effect on electronic equipment is
often more serious, ranging from operational disruption to actual component damage. These effects result
from the high voltages that may be developed. The simple act of walking across a carpet may develop as
much as 30,000 volts, and changing a bed sheet may create a charge of 100,000 volts or more. Such
voltages readily cause arcing (the spark that can be observed when you grab a doorknob after walking
across a carpet, etc.). The arcing is evidence of the discharge path. Due to the high voltage involved, the
discharge current can jump to any nearby metallic or nonmetallic object. If the discharge is to or through
an electronic device, such as the nurse call system, the operation of the device may be affected. If the dis-
charge current passes through internal components, these components may be damaged or their operation
degraded.
What Can We Do About It? The manufacturer of the nurse call equipment has already taken steps to
protect the equipment from electrostatic discharge (ESD) effects. Our peripheral equipment has been
tested and listed by UL
®
to withstand discharges of up to 30K volts. However, since the cause is not in
the equipment, but in the environment, further measures are required of the installer and the user to
achieve complete protection.
What the Installer Can Do: In humid climates or in places where the relative humidity is kept at 65%
or greater, there will likely be few problems with ESD. Where problems may occur the following meas-
ures can be taken.
l Ground all exposed metal surfaces. Grounding should be to a #16 gauge or larger conductor.
l Install nurse call system wiring in metal conduit. This conduit may be used to ground panels.
l Use shielded cable (where specified) for nurse call system station-to-station wiring. The use of
open conductors invites inductive coupling of discharge currents, which can cause the same prob-
lems as direct discharge currents.
l Ground your body before handling system components. This can be done by using a wrist strap,
or simply by contacting a grounded metal surface. Use caution to avoid hazardous voltages while
grounded.
What the User Can Do: The most common generation of ESD in hospitals is due to changing linen on
hospital beds while the patient call cord or pillow speaker is still connected to the nurse call system.
The following precautions will help.
Remove the call cord or pillow speaker from the bed before changing the linen. It will be necessary for
the nursing staff to discharge themselves by contacting a grounded metal object before placing the call
cord or pillow speaker back on the bed; otherwise a spark will jump to the nurse call equipment, caus-
ing the very damage they are trying to avoid. To avoid a shock while discharging static electricity on
the body, hold a metal object, such as a key, and use that object to contact the grounded surface.
This information is provided to make you aware of ESD problems so that precautions may be taken to
avoid damage and disruption of system operation.
4|IL1057 Tek-CARE300III Installation Manual
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TekTone Sound and Signal Mfg., Inc. All Rights Reserved
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