Siemens S120 Manual page 80

Mains connection and line-side power components
3.9 Line connection variants
Note
Line connection of motors
In combination with the drive system, the motors are generally approved for operation on TN
and TT systems with grounded neutral point and on IT systems.
In use on IT systems, the occurrence of a first fault between a live part and ground must be
signaled by a monitoring device. The first fault must be removed as quickly as possible to
minimize temporary overload of the motor insulation.
In all other systems, except TN and TT systems with grounded neutral point and IT systems,
such as systems with a grounded line conductor, an isolating transformer with grounded
neutral point (secondary side) must be connected between the supply and the drive system
in order to protect the motor insulation from continuous excessive stress.
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Manual, (GH6), 04/2014, 6SL3097-4AL00-0BP4
AC Drive