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Figure 22. Jumper locations at the inputs
7.E.9
RS 485 for Cascade (Lead Lag)
Cascade - Prior to wiring units for cascade operations,
select one unit as the lead boiler. Other units
connected to the lead boiler 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 65, 66, and 67
(See Figure 19 on page 36). Use 2-wire twisted
pair, shielded w/drain (communication cable) between
units. Connect one wire of the communication cable to
A (-), terminal 66, and the other wire to terminal B (+),
terminal 65, and a third conductor to GND, terminal 67
(see RS485 NOTE: Grounding). Connect the other end
of the cable to the next unit, matching the termination
wiring on the previous unit. 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.
Section 8.D.4 on page 74 shows how these systems
are configured in the touchscreen controls.
7.E.10 RS485 BMS
BMS – If communicating to the unit via RS485 serial
communications, either Modbus or BACnet MSTP,
connect to terminals 68, 69, and 70 (See Figure 19 on
page 36). Use 2-wire twisted pair, shielded w/drain
(communication cable) between units. Connect one wire
of the communication cable to A (-), terminal 68, and
the other wire to terminal B (+), terminal 69, and a third
conductor to GND, terminal 70.
FT
Section 8.D.11.d on page 94 shows how these
systems are configured in the touchscreen controls.
If changes are made to the RS485 settings, the boiler
power will need to be cycled in order for the changes to
take effect.
NOTE: A system supply sensor (supplied with each unit)
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.
NOTE: RS485 Grounding & Shielding
Grounding: To ensure that common mode voltage does not
compromise the date, or damage the equipment, an extra
wire should always be used to connect the signal grounds.
This means that a 'two-wire' system actually requires
three conductors. Although it is possible to obtain cable
with a twisted pair and a third conductor, it is simpler to
use a cable with an extra twisted pair and use one or both
conductors for the signal ground.
Shielding: It is often difficult to make a clear determination
as to whether shielded cable is required in an application.
Since the added cost of shielded cable is usually minimal,
in most cases it is worth installing. If shielded cable is used,
the shield should be grounded at one end only, preferably
to earth ground. It is not recommended to use a shield drain
wire as the signal ground.
Page 43
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