Fire-Lite LED-10 Series Remote Fire Annunciator User Manual

Page 20

Document 50400 Rev B 10/27/97 P/N 50400:B

Section Four: EIA-485 Shield Terminations

The EIA-485 circuit must be wired using a twisted-shielded pair cable having a charac-
teristic 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 V

RMS

, motor control circuits, or SCR power circuits

Note: To ensure static (ESD - electrostatic discharge) protection, all enclosures,
including the LED-10 Series electrical box, must be connected to earth ground! Never
use the EIA-485 shield for this purpose. The EIA-485 shield is for radiated noise
emission protection (RFI, EMI). Refer to the following figures.

The EIA-485 shield should be terminated as follows:

When the EIA-485 shield is not in conduit: The EIA-485 loop allows the FACP to
communicate with the annunciators. The shield for the EIA-485 loop must be
connected to earth ground at the FACP but must be left floating (no connection) at
the annunciator if it is the first or only device on the EIA-485 loop. If a second
annunciator is connected, the shield leaving the first annunciator must be left
floating. The shield entering the second annunciator must be connected to the 3-
gang box or Earth Ground terminal (TB1-6 & 7) on the second annunciator. If
additional annunciators are connected, the shield leaving each enclosure must be
left floating and the shield entering each must be connected to the 3-gang box or
the Earth Ground Terminal (TB1-6 & 7) on the annunciator.

(+) EIA-485

(-) EIA-485

FACP

Shield Drain Wire

Connect the drain wire to the
outside of the MS-5210UD cabinet
via a BX-type connector.

FACP Backbox

Series