Overcurrent Protection - Siemens SINAMICS S120 Equipment Manual

Cabinet Configuration and EMC Booksize
6.3 24 V DC supply voltage
6.3.4

Overcurrent protection

Cables on both the primary and the secondary side of the power supply unit must be
protected from overcurrent. Primary side protection must be implemented according to the
manufacturer's instructions. Secondary side protection must be rated to deal with the actual
conditions. In particular:
• Loading due to loads, possibly the simultaneity factor in response to machine operation
• Current capacity of the conductors used and cables in normal and short-circuit conditions
• Ambient temperature
• Cable bundling (e.g. laying in a common duct)
• Cable laying method to EN 60204-1
EN 60204-1, Section 14, can be used to determine the overcurrent protection devices.
The recommended overcurrent protection devices on the primary side are circuit-breakers as
specified in Siemens catalog NSK.
The recommended overcurrent protection devices on the secondary side are MCBs. The
MCBs can be selected according to Siemens catalog I1.2.
The 24 V DC power supply of booksize
• Line modules
• Motor modules
• Braking modules
• Capacitor modules
• Control supply modules
is implemented in the components by means of a 24 V busbar for 24 V DC and reference
potential. The current capacity of these bars is 20 A. The power supply is connected via a 24
V terminal adapter. MCBs are recommended to protect the cables from overcurrent. These
overcurrent protection devices also protect the 24 V busbars. To protect against ground
faults, the ground potential must be connected to the protective conductor system.
6-10
Equipment Manual, (GH2), 04.2004 Edition, 6SL3097-2AC00-0BP0
Booksize Power Sections