Installation
ABB Control - AC 31 Page 4-7
1SBC 260400 R1001-b 06.99
1.4. Cabling of the CS 31 bus
The CS 31 bus is a RS 485 serial interface and consists of a shielded twisted pair. This bus is
a master slave bus and only accepts a single master.
Use a AWG 24 (0.22 mm
2
) to AWG 18 (0.18 mm
2
) twisted pair.
The maximum length is 500 m.
The same cable type should be used for the whole system bus setup.
Bus interruptions should be avoided, during cabinet cable connections for instance, otherwise
it should be cabled to the same side of the terminal block (see Figure 4-3 and Figure 4-4).
Warning: STAR connection of the bus is not permitted!
(see Figure 4-5 and Figure 4-6).
The central and remote units may be connected at any point of the bus:
- bus 1 on bus 1
- bus 2 on bus 2
- shielding (preferably braided) on terminal 3 of terminal block 1 and earth connected at
the master level (cable < 1 m)
The bus should be terminated with a 120 Ω 1/4 W resistance connected to the bus
extremities. The twisted pair should be symmetrical (see Figure 4-7 and Figure 4-8).
Connecting the bus shielding to the earth is recommended, with the intercalation of a 1 nF
class Y condenser directly at the cabinet entry, according to the assembly diagram (see Figure
4-9), if noise generating devices are near to the cabinet.
As the CS 31 bus is opto-isolated, it is possible to place elements with different voltage power
on the bus.
Refer to the respective descriptions if a bus amplifier or amplifier with bus redundancy is used.
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