Siemens SIMATIC ET 200S Installation And Operating Manual page 66

Fail-Safe Modules
7.2 PM-E F pm DC24V PROFIsafe Power Module
Switching grounded loads
If the PM-E F pm DC24V PROFIsafe switches loads that have a connection between chassis
and ground (for example to improve the EMC properties) and if chassis and ground are
connected in the power supply being used, a "short circuit" will be detected.
From the perspective of the F-module, the M switch is bridged by the chassis-ground
connection (refer to the following figure as an example of a PM-E F pm DC24V PROFIsafe).
Remedy:
• Use the PM-E F pp DC24V PROFIsafe
• The value of the resistance between chassis and ground at the load end must be greater
Figure 7-2
7-6
than 100 kΩ
Connecting Grounded Loads (resistance exists between chassis and ground)
ET 200S Distributed I/O System - Fail-Safe Modules
Hardware Installation and Operating Manual, 07/2005, A5E00103686-04