T3A Transmitter • 19
Connecting Relays/Alarms
The T3A relays are commonly used to power and control external alarming devices, such as
alarm lights (visual) and horns (audio).
NOTE:
Relays are protected by replaceable 4A fuses.
1. If necessary, unscrew the enclosure lid and pull the internal system out by the
thumbscrews.
CAUTION:
Be sure power to the T3A is off before pulling out the internal system.
2. Locate the relay terminal blocks on the radio/relay board.
WARNING: Use appropriate construction technique to maintain the explosion proof
classification of the assembly.
3. Connect the alarm device’s power (RED) terminal to the
NO
or
NC
terminal on the relay
terminal block.
NOTE:
It is recommended that the relay connections are wired as normally-open (NO).
However, normally-closed (NC) wiring configurations provide an inherent fail-safe
and may be preferred.
4. Connect the alarm device’s ground terminal (GREEN) to an external power source’s “-”
terminal.
Table 4: T3A Terminal Block Wire Gauges
Terminal Block
Wire Gauge
Power terminal
Min: 26 AWG
Max: 14 AWG
Relay 1 & 2 terminal
Modbus terminal
Min: 26 AWG
Max: 16 AWG
Fault terminal