AERCO BMS II BOILER - Manual (Page 22)

INSTALLATION
2-10
Method 1
For Method 1, the bias switches in the BMS II are left in the deactivated (up) position. ). Bias and
termination are controlled at the boiler end of the RS485 loop by activating the bias and termination DIP
switches on the PMC board of the last C-More Control Box on the daisy-chain. Refer to sheet 1 of Figure
2-7 (Benchmark), or Figure 2-8 (KC1000) and proceed as follows:
1. Using a daisy-chain wiring configuration, connect the RS485 positive lead to the RS485 COMM +
terminal in the I/O Box for each boiler.
2. Connect the RS485 negative lead to the RS485 COMM - terminal in the I/O Box for each boiler.
3. DO NOT terminate the shields to the Ground (G) terminal at the boiler end of the RS485 loop.
Connect the shields of the incoming and outgoing leads together. The RS485 loop shield should only
be terminated at terminal 3 of the BMS II.
4. At the last boiler in the daisy-chain, activate the BIAS1, BIAS2 and TERM switches on the PMC board
in the C-More Control Box. Refer to GF-114, paragraph 4.3.2 for detailed instructions on accessing
the PMC board.
5. DO NOT activate the bias switches on the BMS II. These switches must be in the up position when
using Method 1.
NOTE
The advantage of using Method 2 is that the bias and termination of the
RS485 loop do not require any changes to be made to the DIP switches
on the PMC board in the last C-More Control Box.
Method 2
For Method 2, bias is controlled at the BMS II by setting the two bias switches (Figure 2-6) to the active
(down) position. Termination at the boiler end of RS485 loop is accomplished by installing a 120 ohm, 1/2
Watt termination resistor in the I/O Box of the last boiler on the daisy-chain. Refer to sheet 2 of Figure 2-7
(Benchmark), or Figure 2-8 (KC1000) and proceed as follows:
1. Using a daisy-chain wiring configuration, connect the RS485 positive lead to the RS485 COMM +
terminal in the I/O Box for each boiler.
2. Connect the RS485 negative lead to the RS485 COMM - terminal in the I/O Box for each boiler.
3. DO NOT terminate the shields to the Ground (G) terminal at the boiler end of the RS485 loop.
Connect the shields of the incoming and outgoing leads together. The RS485 loop shield should only
be terminated at terminal 3 of the BMS II.
4. At the last boiler in the daisy-chain, install a 120 ohm, 1/2 Watt termination resistor across the RS485
COMM + and - terminals in the boiler’s I/O Box.
5. When using Method 2, activate the two bias switches in the BMS II (Figure 2-6) by placing them in the
down position.