Danfoss VLT AutomationDrive FC 301 Series Design Manual page 190

RS-485 Installation and Set...
12 RS-485 Installation and Set-up
12.1 Installation and Set-up
12.1.1 Overview
RS-485 is a two-wire bus interface compatible with multi-drop network topology, that is, 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 one network segment.
Repeaters divide network segments, see Figure 12.1.
Figure 12.1 RS-485 Bus Interface
12 12
NOTICE!
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 adjustable frequency drives or a
biased termination resistor network. 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 connector. It may be necessary
to apply potential-equalizing cables to maintain the same ground potential throughout the network - particularly in instal-
lations with long cables.
To prevent impedance mismatch, always use the same type of cable throughout the entire network. When connecting a
motor to the adjustable frequency drive, always use shielded motor cable.
Cable
Impedance [Ω]
Cable length [m]
Table 12.1 Cable Specifications
188
Design Guide
Shielded twisted pair (STP)
120
Max. 4,000 ft [1,200 m] (including drop lines)
Max. 1,650 ft [500 m] station-to-station
Rev. 2014-04-04 All rights reserved. MG33BF22