Schlage PIB300 User Manual page 327

Connect the Cable
Master's Ground
Carry a Ground
Line to Each
Unit
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.
Master
GND T+ T-
Do Not Connect
Shield to the the Cable Shield
at this End
All units are connected to the same earth ground. Each shield ground is connected to
only one unit, then interrupted to prevent the formation of ground loops. Two sets of lines
are wired as shown in Figure 2-3. It does not matter significantly which unit's GND is used
for a particular shield, as long as the path is broken from unit to unit.
The second method of establishing a ground reference in a system with floating power
supplies is to use the ground line in the RS-422 cable to establish a common reference
voltage for the communication signals. This line should be connected to the negative
power terminal on the data converter or the ground line in the RS-232 port from the host
PC system. It should then be carried to one of the ground terminals on the back of each
Master
GND T+ T-
Connect the Cable
Shield to the
Master's Ground
Figure 4-4: Communication Shielding Carrying a Single Ground to Each Unit
If no earth ground is available at the units, this is the only possible method of connecting
the grounds. Even if an earth ground is available, depending on the building's power
wiring and other environmental issues, this method may be superior to the previous one,
since it establishes the ground of each unit independently of the building power lines.
Local variations in grounds between buildings, or from one point to another in a very large
building, (perhaps due to elevator motors or other large-current drawing machines) will
have no effect on the communication network if this configuration is used.
However, the power supplies must be truly floating, with no hidden paths back to the
high-voltage side of the transformers, or to earth ground. Since this is difficult to achieve
(there is always some parasitic capacitance between the primary and secondary in any
transformer), this method may be more susceptible to high-frequency transients in the
high-voltage side of the power lines than the earth-grounded method.
Remote 1
GND R+ R-
Connect the
Cable Shield to
Remote 1's
Ground
Do Not Connect
the Cable Shield
at this End
Figure 4-3: Communication Shielding With All Units Earth Grounded
Remote 1
GND R+ R-
Connect Both Shields
to Remote 1 Ground
HandKey II Manual
Remote 2
GND R+ R-
Connect the
Cable Shield to
Remote 2's
Ground
Do Not Connect
the Cable Shield
at this End
Remote 2
GND R+ R-
Connect Both Shields
to Remote 2 Ground
To Next
Remote
To Next
Remote
Connect Shield
to Next Remote
11