Conductor
Pair Shield
Pair separator
Jacket
Separator
Overall shield
Drain wire
en07000139.vsd
IEC07000139 V1 EN-US
Figure 46: Cross section of communication cable
The EIA standard RS-485 specifies the RS485 network. An informative excerpt is given in
section
"Installing the serial communication cable for RS485 SPA/IEC".
6.4.2 Installing the serial communication cable for RS485 SPA/IEC
SEMOD176342-192 v3
Informative excerpt from EIA Standard RS-485 - Electrical Characteristics of Generators and Receivers
for Balanced Digital Multipoint Systems
RS-485 Wire - Media dependent Physical layer
1
Normative references
EIA Standard RS-485 - Electrical Characteristics of Generators and Receivers for Balanced Digital
Multipoint Systems
2 Transmission method
RS-485 differential bipolar signaling
2.1 Differential signal levels
Two differential signal levels are defined:
A+ =line A positive with respect to line B
A- =line A negative with respect to line B
2.2 Galvanic isolation
The RS485 circuit shall be isolated from ground by:
Riso ≥ 10 MW
Ciso ≤ 10 pF
Three isolation options exist:
a) The entire node electronics can be galvanically isolated
b) The bus interface circuit can be isolated form the rest of node electronics by
optoisolators, transformer coupling or otherwise.
c) The RS485 chip can include built-in isolation
2.3 Bus excitation and signal conveyance
Table continues on next page
1MRK514026-UUS Rev. P Section 6
Connecting
670 series 71
Installation manual
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