OMM-0153_E
• 5/11/2023 Technical Support • (800) 526-0288 • Mon-Fri, 8 am - 5 pm EST Page 81 of 124
CENTURION Installation, Operation & Maintenance Manual
SECTION 8: WATER HEATER MANAGEMENT
Figure 8-11: Typical Daisy-Chain Modbus/RS485 Network
NOTE:
WHM Manager does
n’t necessarily have to be on either end of the Daisy-Chain loop.
Any one of the Edge WHM units included in the Modbus network can be the Manager.
However, it is recommended that you decide which unit will be the Manager and which will be
the last unit on the daisy-chain prior to performing the wiring connections. This will simplify
wiring connections and Modbus address assignments.
Modbus network wiring connections must be made using shielded twisted-pair wiring, (18
– 24
AWG) such as Belden #9841, #3105A, #8760, or equivalent. The Modbus wiring connections
are made at the BST/WHM RS485+, BST/WHM RS485- and RS485 ISO GND terminals on the
I/O board included with each Edge Controller.
To Connect Modbus wiring:
1. Starting at the first unit, connect the twisted, shielded pair cable to the BST/WHM RS485
plus (+) and minus (-) terminals on the left side I/O board, RS485 ISO GND (
Error!
Reference source not found.
).
2. At the I/O board of the first unit in the daisy chain (not necessarily Manager), activate the
DIP switch
labeled “MODBUS TERM” by placing it in the up position. This will connect a
termination resistor across the terminals at the source end.
3. Refer to Figure 8.7-3 and run the shielded cable to the next unit in the daisy-chain and
connect the + and
– wire leads (+ to +, - to -). DO NOT connect the shield of the RS485
Comm leads to the SHIELD terminal at the Client. Instead, connect the shields of the
incoming and outgoing RS485 leads together. Shield must be connected only at one
location in the daisy chain.
4. Continue connecting the + and - wire leads and shields for the remaining units as described
in step 3 for the remaining Client units in the chain.
5. At the end
unit in the chain, activate the DIP switch labeled “MODBUS TERM” by placing it
in the up position. This will ensure the termination resistors are activated at both ends.