Johnson Controls NIE39 Installation Instructions Manual page 13

Table 4: Rules for M-Bus Protocol
Category
Line Length and Type
Cable
Termination
1 Unit load is a defined standby current. A device is permitted a current drain of one unit load by default but may consume
more if it is shown at the device (as an integer) and in documentation.
2 Use M-Bus Repeaters to increase the length and the number of unit loads permissible.
Table 5: Rules for KNX Protocol
Category
General
Number of Devices
Line Length and Type
Cable
NIE39/NIE49 Installation Instructions
Rules and Estimated Maximums
Length depends on cable resistance, capacitance, number of devices, position of devices, and
configured communication speed. Example scenarios to help with calculation:
Baud Rate Maximum Number of
Unit Loads
2400 64
64
250
9,600 64
250
38,400 64
Twisted pair cable (shielding optional)
No termination
Rules and Maximums Allowed
No restrictions in topology
Depends on chosen topology and cable type.
Twisted pair cable recommended; length depends on cable resistance, capacitance, number devices,
position of devices, and communication speed.
Copper, solid and stranded wires with outer sheath, one- or two-twisted pair; 0.8 to 1.0 mm (20 to 18
AWG)
Screen is required and must cover the entire diameter.
Drain wire: Diameter minimum 0.4 mm (26 AWG)
Maximum Distance
, Between Converter and
1 2
Devices
3,000 m (9,842 ft)
1,000 m (3,281 ft)
350 m (1,148 ft)
350 m (1,148 ft)
350 m (1,148 ft)
350 m (1,148 ft)
Maximum Distance for
Entire Bus
5,000 m (16,404 ft)
(2 x 1.0 mm [18 AWG],
shield recommended,
resistance < 90 Ohms)
4,000 m (13,123 ft)
(2 x 1.0 mm [18 AWG],
shielded, resistance < 90
Ohms)
4,000 m (13,123 ft)
(2 x 0.8 mm [20 AWG],
shielded, resistance < 30
Ohms)
4,000 m (13,123 ft)
(2 x 0.8 mm [20 AWG],
shielded, resistance < 30
Ohms)
1,000 m (3,281 ft)
(2 x 0.8 mm [20 AWG],
shielded, resistance < 30
Ohms)
1,000 m (3,281 ft)
(2 x 0.8 mm [20 AWG],
shielded, resistance < 30
Ohms)
13