Step 1: MODBUS HEADER TEMP SENSOR WIRING – ANY BOILER
1. Connect the Modbus Transmitter terminal Pin B to the I/O board strip J3, terminal 13
(BST RS485+) and Pin A to terminal 15 (BST RS485–) on any of the Boiler units using
shielded pair 18 - 22 AWG cable.
2. Connect the shield to any Shield terminal, such as terminal 3 or 8 on strip J3.
2. Connect the Header Temp Sensor to pins 2 and 3 of the Modbus Transmitter using
shielded pair 18 - 22 AWG cable.
3. Install a jumper wire between pins 1 and 2 of the Modbus Transmitter.
NOTES:
• Polarity must be observed for the RS485 connections.
• Ground the shield to any Shield terminal on the I/O board, such as terminal 3.
• The Header Temp Sensor must be installed between 2 and 10 feet (0.61 and 3.1m)
downstream of the LAST boiler in the plant’s supply water header.
• There is no polarity to be observed. The ground for the shield is at the power supply
ground. The sensor end of the shield must be left free and ungrounded.
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