RCCB for 4-wire circuits, Type A sensitivity
The Siemens 5SM1352-6 is a 4-pole residual current circuit breaker (RCCB) from the SENTRON 5SM1 series, rated 25 A at 500 V AC with a 30 mA trip threshold and Type A fault-current detection. Type A means it responds to sinusoidal AC residual currents plus pulsed DC — the standard choice for circuits feeding single-phase rectifiers, switching power supplies, and variable-speed drives where smooth DC fault currents can blind a basic AC-only RCCB. The 30 mA sensitivity covers personnel protection (≤ 30 mA is the IEC threshold for direct-contact shock protection).
Thermal derating and conductor sizing
Full 25 A rating holds at 40 °C and 45 °C. Above that the current must be derated: 24 A at 50 °C, stepping down to 20 A at 70 °C. The terminal range accepts 1.5 mm² minimum to 25 mm² maximum — the 25 mm² upper limit covers most 25 A feeder conductors in copper, so no lug adapter is needed for standard panel wiring. The I²t withstand is 70 000 A²·s, and the short-circuit current rating is 10 kA, meaning it can interrupt a fault up to that level without upstream damage.
DIN-rail fit and panel integration
Snaps onto standard DIN rail (REG profile), occupies 4 width units (roughly 72 mm at 18 mm per unit), and installs 55 mm deep into the enclosure. Mounting position is unrestricted — top or bottom feed is acceptable. The IP20 rating applies once the distribution board is closed and conductors are connected; the enclosure itself provides the environmental seal. Finger and back-of-hand touch protection is built in, meeting the shock-protection requirements for live-terminal access inside a locked panel.