LAARS Heating Systems
Page 38
7.D.7 RS 485, Cascade
Cascade - Prior to wiring units for cascade operations,
select one unit as the lead boiler/heater. Other units
connected to the lead boiler/heater will be referred to as
lag units. Communication between lead and lag units
is accomplished using RS485. When wiring these units
for cascade operations, use terminals 57, 58, and 59
(See Figure 19 on page 35). Use 2-wire twisted pair,
shielded w/drain (communication cable) between units.
Connect one wire of the communication cable to A (-),
terminal 58, and the other wire to terminal B (+), terminal
57, and the drain wire to GND, terminal 59. Connect
the other end of the cable to the next unit, matching the
termination wiring on the previous unit, except for GND.
Only connect the drain wire to ground on one end of
the cable to avoid ground loop issues. If more than two
units are cascaded together, daisy chain the wiring from
unit to unit, keeping the cables as short as possible. A
system supply sensor must be installed and connected
to the lead boiler. The lead boiler will use this system
supply sensor as the temperature control sensor for
cascade operations. TT1 terminals are used to initiate a
heat demand at the lead boiler.
Section 8.D.4 on page 71 shows how these systems
are configured in the touchscreen controls.
7.D.8 RS485 BMS
BMS – if communicating to the unit via RS485 serial
communications, either Modbus or BACnet MSTP,
connect to terminals 60, 61, and 62 (See Figure 19 on
page 35). Use 2-wire twisted pair, shielded w/drain
(communication cable) between units. Connect one wire
of the communication cable to A (-), terminal 61, and the
other wire to terminal B (+), terminal 60, and the drain
wire to GND, terminal 62.
Section 8.D.11.d on page 86 shows how these
systems are configured in the touchscreen controls.
