Siemens S7-400 Installation Manual page 39

Mounting Screws
You have a choice of the following types of screw for securing a rack:
M6 cylinder-head screw to
ISO 1207/ISO 1580 (DIN 84/DIN 85)
M6 hex. screw to ISO 4017 (DIN 4017)
Step 3: Connecting the Rack to the Chassis Ground
Connect the rack to the chassis ground. A threaded bolt is provided for this
purpose on the bottom left of the rack.
Minimum cross-section of the conductor to the chassis ground: 10 mm
If the S7-400 is mounted on a mobile rack, you must provide a flexible conductor to
the chassis ground.
Note
Always ensure that there is a low-impedance connection to the chassis ground
(see the figure below). You achieve this with the shortest possible, low-resistance
conductor with a large surface to establish large-area contact.
M6 nut
S7-400 and M7-400 Programmable Controllers Hardware and Installation
A5E00069481-04
Screw Type
M6 threaded bolt
Contact washer
Terminal
Plain washer
Installing the S7-400
Explanation
Choose the screw length according to your
assembly.
You also need "6.4" washers to ISO 7092
(DIN 433).
To chassis
ground
2
.
2-13