What it is and where it lands
The Siemens 5SU9353-1KK20 is a SENTRON RCBO — a combined residual-current circuit breaker and overcurrent protection device in a single 2-module-wide (36 mm) housing. It protects a single-phase final subcircuit (1P+N, neutral switched) against earth faults (30 mA, type AC, instantaneous) and overload/short-circuit (C-curve, 20 A, 4.5 kA breaking capacity per EN 60898). This is a DIN-rail component for distribution boards and sub-distribution panels. The 36 mm width and 77 mm depth fit standard modular enclosures; supply can enter from top or bottom, and the mounting position is unrestricted.
Key ratings and what they mean for fit
The 20 A rating at 30 °C (ambient) with C-curve tripping means it handles inrush from motorized or capacitive loads without nuisance trips — typical for lighting banks, small pumps, or socket circuits in commercial and light industrial panels. The 4.5 kA breaking capacity (per EN 60898) is the standard domestic/commercial short-circuit withstand; for industrial panels with higher prospective fault current, verify the upstream device limits. The 30 mA residual-current element (type AC, instantaneous) detects sinusoidal AC earth faults only — not pulsed DC or smooth DC. If the downstream load includes VFDs, LED drivers, or single-phase rectifiers, a type A or F RCBO would be required instead. Rated insulation voltage (Ui) is 264 V, overvoltage category III, pollution degree 2 — standard for fixed-installation final circuits. Surge voltage withstand is 4 kV, and surge current withstand (8/20 µs) is 1 kA. Operating frequency is 50/60 Hz, supply voltage 230/240 V AC.
Panel integration notes
The device occupies 2 modular width units (36 mm) on a DIN rail. Installation depth is 70 mm plus the 77 mm overall depth allows for wiring space in standard 150 mm deep enclosures. The IP20 rating applies only when the distribution board is installed and conductors are connected — not for open-panel or wet-area mounting. Power dissipation per pole in hot operating state is 0.75 W at rated current — relevant for thermal derating in multi-device enclosures. Halogen-free and silicon-free construction simplifies disposal compliance and avoids outgassing concerns in sealed cabinets.