Siemens SIMATIC NET OLM12M Description And Operating Manual page 73

6ZB5530–3AB00–0BA0/01
Connecting the Electrical RS485 LAN Cables
For the RS 485 LAN cable, use only shielded twisted pair SIMATIC NET cables for PROFIBUS.
Make sure that the same wires (green or red) are connected consistently to the same terminal A or
B for all bus attachments in a segment.
For PROFIBUS field bus networks, the following is recommended:
Terminal A (RxD/TxD-N): green wire
Terminal B (RxD/TxD-P): red wire
Do not connect RS 485 LAN cables that are laid entirely or partly outside buildings. Otherwise,
lightning strikes in the vicinity could destroy the modules. If LAN connections exit buildings, you
should always use FO cables wherever possible.
Channel 1 is designed as a 4-wire terminal block.
Figure 21: Channel 1 – attachment of a LAN cable to the terminal block
(1=securing flange, 2=shield clip, small)
Connect the RS 485 LAN cable to the terminal block as shown in Figure 21.
The terminals indicated as A or B are electrically identical.
Figure 22: Channel 1 – attachment of two LAN cables to the terminal block
(1=securing flange, 2=shield clip, large)
It is possible to connect two RS485 LAN cables with a cross sectional area of 2 x 0.65 mm
terminal block, for example to create an active PROFIBUS star coupler.
Note that the bus cables must be connected to the OLM12M as shown in Figure 22.
Make sure there is good electrical contact between the braid shield and the shield clip.
If necessary, fold back the braid shield over the outer sheath of the LAN cable. This increases
the diameter of the cable and allows a single LAN cable to be clamped more firmly.
If the RS485 LAN cable is subject to strain, provide external strain relief.
Secure the terminal block by screwing the securing flanges.
Copyright Siemens AG 1997
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