What it is and what it does
The Siemens 5SU9346-1CN25 is a 4-pole RCD-operated circuit breaker (RCBO) from the SENTRON 5SU9 series, combining overcurrent protection and residual current detection in a single DIN-rail mounted unit. Rated 25 A at 30 °C with a Type C tripping characteristic, it handles moderate inrush loads like motor starters and capacitor banks. The 6 kA breaking capacity per EN 60898 and IEC 60947-2 covers most residential and light commercial fault levels — enough for a sub-distribution board in a small factory or a multi-family building. The RCBO detects AC fault currents only (Type AC) and trips instantaneously — no time delay, so it reacts to earth faults without intentional lag. That means it's suited for general-purpose circuits where nuisance tripping from transient leakage is unlikely, but not for circuits with downstream electronics that generate smooth DC fault currents.
Ratings and what they mean for fit
The 25 A rating is at 30 °C ambient. At 40 °C it derates to 23.3 A, at 45 °C to 22 A, at 50 °C to 21.5 A, and at 55 °C to 20.8 A. If the panel runs hot — say inside a non-ventilated enclosure near other heat sources — the effective ampacity drops. Size the upstream protective device and cable accordingly. The 6 kA rated short-circuit capacity per both EN 60898 and IEC 60947-2 means it can safely interrupt a fault up to 6 kA at the rated voltage. Overvoltage category III qualifies it for fixed installation downstream of the main distribution board, not for plug-in portable equipment. Terminals accept solid or stranded conductors from 0.75 mm² up to 35 mm² — covers everything from 1.5 mm² lighting circuits to 10 mm² feeder tails. The 77 mm depth and 70 mm installation depth fit standard 80 mm deep enclosures; the 126 mm width (7 modular width units) means it occupies 7 x 18 mm on the DIN rail.
Lifecycle and sourcing reality
Halogen-free and silicon-free construction means it meets the material restrictions common in rail, marine, and high-reliability building specs. Touch protection is built in — no separate finger-safe covers needed after installation.
Panel integration notes
Mounts on a standard 35 mm DIN rail; any mounting position is allowed. Supply can enter from top or bottom — no orientation restriction, which simplifies busbar routing in crowded enclosures. IP20 rating applies only when the distribution board is installed and conductors are connected; the front face is finger-safe, but the terminals are not sealed against dust ingress before wiring. Power loss is 2.25 W maximum at rated load — negligible for thermal budgeting in a multi-way board, but worth summing if the enclosure holds 20+ RCBOs.