Honeywell CENTRA LINE MERLIN N Series Manual page 22

MERLIN NX IP AND MST/TP VAV CONTROLLER - INSTALLATION INSTRUCTIONS
— Ground noise should not exceed the EIA-485 com-
mon mode voltage limit.
— Must conform to TIA/EIA 485 cabling guidelines.
"TIA/EIA 485 Cable Specifications" on page 16.
IP/MSTP VAV
CONTROLLER
(MASTER)
NOTE:
1) If any of the devices are not electrically isolated, it is recommended that those devices be connected to the ground terminal (V0).
2) The 120-Ohm termination resistor must be inserted directly into the terminals of both end devices.
3) If shielding is used, the shielding of each individual bus segment should be separately connected at one end to earth.
4) Always power each controller and the connected slaves via separate transformers.
5) Between devices equipped with non-isolated RS485 bus interfaces, potential differences of max. ±7 V are allowed. Further, this bus should not extend beyond a single building.
Fig. 26. Modbus Master Controller and Connected Modbus devices (with inserted termination resistors)
EN1Z-1076GE51 R1021
— Should not extend beyond a single building.
— It is recommended that you select a low baud rate
See (for example, 19.2 kbps) for reliable operation
.
L*
MODBUS
DEVICE #1
22
MODBUS
DEVICE #2
MODBUS
DEVICE #..N