LCD2-80 Instruction Manual — P/N 53242:B5 07/26/2019 19
Appendix A: EIA-485 Shield Terminations
The EIA-485 circuit must be wired using a twisted-shielded pair cable having a Characteristic Impedance of 120 ohms, +/- 20%. Do not
run cable adjacent to, or in the same conduit as, 120-volt AC service, noisy electrical circuits that are powering mechanical bells or
horns, audio circuits above 25 Vrms, motor control circuits, or SCR power circuits. All enclosures, including the FACP backbox, must be
connected to earth ground! Never use the shield for grounding purposes.
Note on remote power supplies:
When the LCD2-80 is powered from a separate power supply, use a separate conductor to connect the main power supply common ter-
minal to the remote power supply common terminal. Disable earth fault detection on the remote power supply.
When employing the LCD2-80 in Terminal Mode:
Terminate the EIA-485 shields at either the cabinet (when not in conduit) or at system common (when in conduit) as outlined below.
When the EIA-485 shield is not in conduit: At each respective LCD2-80 enclosure (except the first on the loop), terminate the shield
coming in from the previous LCD2-80 at the outside of the cabinet backbox (earth ground). Let the outgoing (to next LCD2-80) shield
float (no connection). Shield termination between LCD2-80s can only occur at the receiving end - the end connected to P1 Terminals 2
and 4.
When the EIA-485 shield is in conduit: At each respective LCD2-80 enclosure (except the first on the loop), terminate the shield coming
in from the previous LCD2-80 at system common. Let the shield going out to next LCD2-80 shield float (no connection). Shield termi-
nation between LCD2-80s can only occur at the receiving end—the end connected to LCD2-80 P1 Terminals 2 and 4.
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