What it is and what it does
The Siemens SENTRON 5SU1342-7KC25 is a 4-pole RCBO (residual current circuit breaker with overcurrent protection) rated at 25 A with a C tripping characteristic and a 30 mA type A residual current sensitivity. It breaks fault currents up to 50 kA per EN 60898 and IEC 60947-2, which means it can safely interrupt high-energy faults on a 400 V three-phase supply without cascading damage upstream. The C curve handles moderate inrush from motor or transformer loads — expect a magnetic trip at 5 to 10 times rated current, so it suits mixed lighting and small-motor circuits where the start-up surge is higher than a B curve would tolerate.
Key ratings and what they mean for fit
The 30 mA type A residual current detection catches pulsating DC fault currents — the kind rectified loads (VFDs, switched-mode supplies, single-phase rectifiers) can produce. Type AC devices miss these; type A is the minimum for modern panels with electronics. The 50 kA breaking capacity at 230/400 V is high for a 2-MW-wide RCBO — it clears faults on strong utility feeds without needing a backup fuse. The 25 A rating and 4-pole switching (neutral is switched too) make it a direct fit for three-phase sub-distribution boards feeding socket circuits or small equipment. Conductor cross-section accepts 0.75 to 35 mm² solid or stranded, which covers everything from 1.5 mm² lighting tails to 10 mm² sub-main cables. Installation depth is 70 mm — check your enclosure depth before committing.
Panel integration notes
The 5SU1342-7KC25 occupies 2 width units (about 36 mm) on a DIN rail. Mounting position is any orientation, which simplifies layout in tight enclosures. The screw terminals take a 2.5 to 3 N·m torque — a standard screwdriver setting, no special tool. Supply can feed from top or bottom, so rework of existing busbar arrangements is minimal. IP20 applies only when the distribution board is installed with connected conductors — the front face is touch-protected (fingers won't reach live parts), but the terminals are not sealed against dust ingress. Ambient temperature range is -25 to +55 °C; storage range is -40 to +75 °C. The 95% humidity tolerance covers most non-condensing environments.
Compliance and documentation
The 5SU1342-7KC25 carries designations per DIN EN 61346-2 and DIN EN 81346-2 (function F). It is halogen-free and silicon-free, which matters for clean-room or sensitive electronics environments where outgassing can cause contact corrosion. Overvoltage category III means it is rated for fixed installation downstream of the main distribution board, not for socket-outlet level. Energy limiting class 3 indicates it limits let-through energy well — relevant for coordinating with downstream devices. The test button operates down to 195 V, so it can be functionally tested even on a weak supply.