Siemens SIMATIC S7-1500 System Manual page 158

Installation
6.2 Installing the mounting rail
3. Insert the spacer, ring terminal with the grounding connector, flat washer, and lock
washer onto the bolt (in that order). Thread on the hexagon nut. Fasten the components
in place with the nut (torque 4 Nm).
4. Connect the opposite end of the grounding cable to the central grounding
point/protective conductor busbar (PE).
5. If you mount the redundant system on separate mounting rails, repeat steps 1 to 4 for the
second mounting rail.
Figure 6-3 Attaching the protective conductor (protective earth)
NOTE
Alternative grounding of the mounting rails
Grounding with the grounding screw is not required if the following requirements are met:
The mounting rails must be permanently connected to the protective conductor system using
an equivalent fitting that complies with the applicable standards, for example by permanent
attachment to a grounded control cabinet wall.
Reference
You can find more information on the exact dimensions of the mounting rails in the appendix
Dimension drawings (Page 366).
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S7-1500R/H redundant system
System Manual, 11/2022, A5E41814787-AD