What it is and what it does
The Siemens 5SU9356-7KN32 is a 2-module-wide (36 mm) RCD-operated circuit breaker — an RCBO — from the SENTRON 5SU9 series. It combines overcurrent protection (MCB function) with residual current detection in a single DIN-rail unit, saving a slot compared to separate breaker + RCD. Rated 32 A at AC with a C tripping curve, it handles motor-start inrush and general-purpose loads in final distribution boards. The Type A fault-current sensitivity means it catches pulsating DC residual currents from electronics or rectifier loads — not just pure sinusoidal AC faults — which is the standard pick for modern panels with switched-mode supplies.
Breaking capacity — which number governs your installation
Two breaking-capacity ratings sit on the nameplate: 6 kA per EN 60898 and 10 kA per IEC 60947-2. The 6 kA figure is the one that governs for residential and light commercial final circuits under the wiring-rule standard. The 10 kA rating applies when the device is used as an industrial circuit-breaker under IEC 60947-2, which allows higher prospective fault current at the point of installation. For a panel builder, the practical takeaway: if your declared SCCR at the board is 6 kA or less, this unit meets it under EN 60898; if the board is rated 10 kA, you rely on the IEC 60947-2 rating — verify the installation category and upstream protection coordination.
Mounting and wiring constraints
Snaps onto 35 mm DIN rail, any mounting position. Depth is 77 mm (installation depth 70 mm), so it clears a standard 80 mm-deep enclosure backplate without crowding. Conductor range: solid or stranded 0.75 to 35 mm² — that 35 mm² upper end handles the full 32 A without needing a ferrule or reducing tail. Supply can enter from top or bottom, which simplifies busbar routing in a crowded board. IP20 with conductors connected and distribution board installed — no washdown rating, so keep it inside the panel.
Thermal derating — the real-world current
The 32 A rating holds at 30 °C ambient. At 40 °C it derates to 30.08 A; at 45 °C to 29.12 A; at 50 °C to 27.84 A; at 55 °C to 25.92 A. If the panel ambient runs hot — say, next to a transformer or in a non-ventilated enclosure — the effective continuous current drops. For a 32 A circuit, a 45 °C ambient knocks off nearly 3 A. Plan the load accordingly or move the RCBO to a cooler zone in the board.