Siemens SINAMICS S120 Combi - Overcurrent Protection in the 24 V Solid-State Circuit

Cabinet design and EMC
12.6 24 V DC supply
SINAMICS S120 Combi
Manual, (GH9), 07/2016, 6SL3097-4AV00-0BP5
297
12.6.3
Overcurrent protection in the 24 V solid-state circuit
The cables on the primary and secondary sides of the 24 V power supply unit must be
protected against overcurrent.
The protection on the primary side depends on the instructions of the equipment
manufacturer.
The protection on the secondary side depends on the actual conditions. Please note the
following:
● Loading from loads, possibly the demand factor against the operation of the machine
● 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)
● Cable routing type
Overcurrent protective devices can be used in compliance with local installation regulations.
Circuit breakers as listed in 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- 2 MCBs by core cross-section and temperature
Core 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.