8 RS485 Installation and Set-up
8.1 RS485
8.1.1 Overview
RS485 is a 2-wire bus interface compatible with multi-drop network topology. The nodes can be connected as a bus, or via drop
cables from a common trunk line. A total of 32 nodes can be connected to 1 network segment. Repeaters divide network segments,
see the following illustration.
e7
5z
a1
45
.1
2
R
+
R
+
R
+
R
+
R
+
R
+
R
+
R
+
Repeater
Repeater
Repeater
Master
1
1
1
1
2
2
2
2
3
3
3
3
30
30
30
31
31
Illustration 63: RS485 Bus Interface
N O T I C E
Each repeater functions as a node within the segment in which it is installed. Each node connected within a given network must
have a unique node address across all segments.
Terminate each segment at both ends, using either the termination switch (S801) of the drives or a biased termination resistor net-
work. Always use shielded twisted pair (STP) cable for bus cabling and follow good common installation practice.
Low-impedance ground connection of the shield at every node is important, including at high frequencies. Thus, connect a large
surface of the shield to ground, for example with a cable clamp or a conductive cable gland. Sometimes, it is necessary to apply
potential-equalizing cables to maintain the same ground potential throughout the network, particularly in installations with long
cables.
To prevent impedance mismatch, use the same type of cable throughout the entire network. When connecting a motor to the drive,
always use shielded motor cable.
Table 49: Cable Specifications
Cable
Shielded twisted pair (STP)
Impedance [Ω]
120
Cable length [m (ft)]
Maximum 1200 (3937) (including drop lines).
Maximum 500 (1640) station-to-station.
AJ363928382091en-000101 / 130R0983 | 101
Danfoss A/S © 2021.04
RS485 Installation and Set-up
VLT® Flow Drive FC 111
Design Guide
