Siemens SINAMICS G150 Operating Instructions Manual page 184

Electrical installation
4.10 Other connections
Note
Ensuring the function of digital inputs
An open input is interpreted as "low".
Terminal M1 must be connected so that the digital inputs (DI) can function.
This is achieved through one of the following measures:
1. Also route the reference ground of the digital inputs.
2. A jumper to terminal M. (Note: This removes the electrical isolation for these digital
inputs.)
Note
If the 24 V supply is briefly interrupted, then the digital outputs are deactivated during this
time.
184
Converter cabinet units
Operating Instructions, 07/2016, A5E03347396A