Siemens SINAMICS PM240-2 Hardware Installation Manual page 43

Protection and monitoring equipment
To provide protection against short-circuit, use the overcurrent devices listed in Technical
data (fuses, circuit breakers etc.).
If the apparent impedance of the line supply at the infeed point is not suitable, so that fuses
do not rupture in the specified time in the case of insulation failure (ground fault, fault to
frame), then you must use additional fault current protective devices RCD (RCCB or MRCD),
type B.
In order that an RCD does not unnecessarily trip as a result of operational leakage currents,
the following preconditions must be fulfilled:
● The neutral point of the line supply is grounded.
● For inverters with rated input currents ≤ 125 A referred to LO, use an RCCB type B with
a response limit current of 300 mA. Connect the RCCB in series with the overcurrent
protective devices.
● For inverters with rated input currents> 125 A referred to LO, use a type B MRCD (for
example, from the Bender company).
An MRCD comprises an RCM (differential current monitoring device), a measuring
current transducer and a circuit breaker with additional undervoltage release, listed in the
Technical data. An example of an MRCD design is provided in the following diagram.
Figure 5-1
● A dedicated RCD is used for every inverter.
● The motor cables are shorter than 50 m (164 ft) shielded, or 100 m (328 ft) unshielded.
Additional information about motor cables
Further protection and monitoring equipment
(https://support.industry.siemens.com/cs/ww/en/view/109486009)
Power Module PM240-2
Hardware Installation Manual, 01/2017, A5E33294624B AE
MRCD
Length of the motor cable (Page 52)
Connecting-up
43