Schlage PIB300 User Manual page 219

There are two standard methods for providing earth grounding to HandPunch
units:
•
•
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
Earth Ground convenient to the unit and the unit's power supply is floating.
All Units
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.
For systems with multiple units on a network, there will be a series of cables
daisy-chained between the units, and the shield of each leg of the network
should be connected to ground at only one end. It does not matter which end.
An example of this method of grounding is shown in Figure 2-3.
earth grounding all units (see Figure 2-3)
carrying an earth ground to each unit (see Figure 2-4)
HandPunch 3000/4000 Manual
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