Siemens SIMOTICS M 1PH8 Configuration Manual page 97

For specific applications, the grounding of the motor Z
grounding of the connected loads Z
mounted in an insulated fashion. In this case, the capacitive discharge (leakage) current of
the motor flows from the motor frame through the motor shaft to the connected load and
from there to ground.
Figure 4-9
The rotor ground current should be avoided by using an electrically insulating coupling. If
such a coupling cannot be used for mechanical reasons, then the motor frame must be
connected to the load through the largest possible surface area. The capacitive discharge
(leakage) current then flows from the motor frame to the load and not through the bearings.
The connection between the motor frame and load is only effective if it represents an
extremely low impedance for the high-frequency discharge (leakage) current. To achieve this,
use several flat straps, e.g. grounding straps, metal plates.
Figure 4-10
1PH8 SIMOTICS M main motors
Configuration Manual, 12/2022, A5E51895839A
Bearing current due to the grounding situation (=rotor ground current)
Connection between the motor frame and load to avoid rotor ground currents
can be more unfavorable than the
hg
, e.g. for long motor cables and when the motor is
rg
Mechanical properties
4.4 Types of bearing
95