SENTRON 5SM1342-6 — 4-pole RCCB, Type A, 25 A, 30 mA
The Siemens 5SM1342-6 is a 4-pole residual current circuit breaker (RCCB) from the SENTRON family, rated 25 A at 400 V AC with a 30 mA trip threshold, Type A waveform sensitivity for pulsating DC and sinusoidal AC fault currents. It is an instantaneous (non-delayed) design — no intentional time lag — so it trips within milliseconds on a ground fault, which makes it the right choice for circuits where fast disconnection is needed and coordination with downstream selective RCCBs is already planned. The 30 mA trip level is the standard for personnel protection (indirect contact) per IEC 61008-1, and the Type A classification means it handles both sinusoidal AC residual currents and pulsating DC waveforms up to 6 mA smooth DC — common from single-phase rectifiers, switched-mode supplies, and LED drivers. A pure Type AC device would miss those pulsating faults, so this part covers the majority of modern mixed-load panels.
Rated 25 A at 40 °C and 45 °C ambient, the 5SM1342-6 derates linearly above that: 24 A at 50 °C, 23 A at 55 °C, 22 A at 60 °C, 21 A at 65 °C, and 20 A at 70 °C. If the panel internal ambient hits 60 °C — not unusual in a crowded enclosure next to contactors — the continuous load must be capped at 22 A. The -25 °C floor matters for unheated enclosures in cold climates; below that, the internal mechanism may not trip reliably.
Short-circuit withstand and selectivity
The rated short-circuit current (Icn) is 10 kA per IEC 61008-1, with an I²t let-through of 70 000 A²·s. The conditional short-circuit rating with an upstream backup fuse or MCB is 0.8 kA per EN 60898. For a panel with a 10 kA prospective fault level at the RCCB terminals, the 10 kA rating is sufficient without an upstream fuse — but if the RCCB is fed from a higher-capacity bus, a current-limiting MCB or fuse ahead of it is needed to keep the let-through energy within the 70 000 A²·s limit. The surge current resistance is rated at 1 kA (8/20 µs waveform), which covers most indirect lightning-induced surges on a TN system.
Snaps onto DIN rail (REG profile), occupies 4 modular width units (MW), and fits standard DIN 43880 size 1 cutouts. Installation depth is 55 mm behind the panel face. The IP20 rating applies only when the distribution board is installed with connected conductors; the terminals are finger-safe only inside an enclosed panel.