Schlage PIB300 User Manual page 43

Planning an Installation
Earth Ground
All Units
10
There are two standard methods for providing earth grounding to HandKey units:
• earth grounding all units (see figure 4-3 on page 11)
• carrying an earth ground to each unit (see figure 4-4 on page 11)
Earth ground all units when there is a good earth ground source near each unit and/or
when there are very long cable runs between units.
Carry an earth ground to each unit when there are no earth grounds convenient to the
unit and the unit's power supply is floating.
One method of establishing a ground reference is to connect each unit's main board
ground to earth ground. Earth ground is found on the third pin on standard AC line
sockets (in the United States, this is the round one in the middle). If the building wiring is
functioning correctly, this should be a low-impedance path to a true ground, which then
serves as a common reference point for the units.
If this method of grounding the units is used, it is not necessary to connect the units in
the network together with a ground line in the communication cable. Indeed, doing so
could create ground loops—large-area loops which provide a good coupling to external
magnetic fields—which may actually compound communication problems. If a magnetic
field, such as that from a lightning strike, induces a voltage in the ground loop, it is
possible for large currents to flow around the loop, which can raise the ground potential
of some units relative to others. When the shield or the cable is connected to any ground
in this configuration, it should be connected only at one end to prevent the formation of
ground loops.
CARD
READER OUTPUTS
INPUT
1 2 3 4 5 6 7 8 9 10
EARTH GROUND CONNECTION PINS
Figure 4-2: Earth Ground Connection Terminals
SWITCH
INPUTS
11 12 13 14