Siemens SIMATIC ET 200M Manual page 213

Compatibility Between the IM 153-x Modules
9.3 RC Network with 1 MW for a Configuration with
Ungrounded Reference Potential
For more on the principle behind this, please read Section 5.1.3.
The following IM 153-x modules have a resistance of 1 MΩ in the RC network:
S IM 153-1 up to and including
153-1AA02, version 07
S IM 153-2 up to and including
153-2AA01, version 02
The Following Applies to This IM 153-x:
You can operate a maximum of 18 nodes on the PROFIBUS-DP in an
ungrounded configuration on one power supply.
If there are more than 18 nodes, you must use an additional power supply.
Subsequent Versions
All subsequent versions have a resistance of 10 MΩ in the RC network.
9-8
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153-1AA82, version 06
22 nF
M
M
L
+
M
24 V DC
Ground bus
1 MW
Distributed I/O Device ET 200M
EWA-4NEB780600602-06