iv • IL380 Tek-CARE
®
NC150 & NC200 Manual
Copyright © TekTone Sound & Signal Mfg., Inc. All Rights Reserved.
A Word about ESD (Electrostatic Discharge)
What Is It? Static electricity is a result of triboelectric charging of two dissimilar
nonconductive materials that are rubbed together, such as rubbing your feet on a carpet
on a cold winter day or in a dry climate. 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 dependant on the materials being rubbed together, humidity, the rate of
separation, 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 non-
metallic 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 discharge 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.
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 measures can be taken.
• Ground all exposed metal surfaces. Grounding should be to a #16 gauge or larger
conductor.
• Install nurse call system wiring in metal conduit. This conduit may be used to
ground panels.
• Use shielded cable for nurse call system station-to-station wiring. The use of
open conductors invites inductive coupling of discharge currents, which can
cause the same problems as direct discharge currents.
• 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, causing 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.
