Siemens SINAMICS S120 - Overcurrent Protection

Cabinet design and EMC Booksize
12.6 24 V DC supply voltage
Booksize Power Units
696 Manual, (GH2), 07/2016, 6SL3097-4AC00-0BP8
12.6.3
Overcurrent protection
The cables on the primary and secondary sides of the 24 V power supply unit must be
protected against overcurrent.
Primary side protection must be implemented according to the manufacturer's instructions.
Secondary side protection depends on the prevailing situation. Please note the following:
● Loading due to loads, including simultaneity factor depending on machine operation
● Current carrying capacity of the conductors used and cables in normal and short-circuit
conditions
● Ambient temperature
● Cable bundling (laying cables in a common duct)
● Type of cable routing
The overcurrent protection devices can be determined according to EN 60204-1, Section 14.
Circuit breakers from the Siemens "NSK" catalog are recommended as overcurrent
protection devices on the primary side.
Miniature circuit breakers or SITOP select (article number 6EP1961-2BA00) are
recommended as overcurrent protection devices on the secondary side. The MCBs can be
selected according to Siemens catalog "BETA Modular Installation Devices - ET B1".
When selecting the miniature circuit breaker, local installation regulations must be carefully
complied with.
Table 12- 5 MCBs by conductor cross-section and temperature
Conductor cross-section
Max. value up to 40 °C
Max. value up to 55 °C
1.5 mm
2
10 A
6 A
2.5 mm
2
16 A 10 A
4 mm
2
25 A
16 A
6 mm
2
32 A 20 A
24 V busbar
20 A
20 A
The trip characteristic of the MCBs must be selected to match the loads to be protected and
the max. current provided by the power supply unit in the event of a short-circuit.