Siemens Simatic M7-400 Reference Manual page 208

Digital Modules
Changing Fuses
Warning
!
This can result in injury.
If you change a fuse without removing the front connector of the module, you could
be injured by an electric shock.
Consequently, always remove the front connector before you change the fuse.
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S7-400, M7-400 Programmable Controllers Module Specifications
A5E00069467-07