What it is and what it does
The Siemens 5SU9356-1KN20 is a SENTRON RCBO — a combined RCD and MCB in one 2-module-wide unit. It protects a single-phase final subcircuit against overload, short-circuit, and earth leakage in one compact package. The 30 mA Type AC residual current detection catches sinusoidal AC fault currents, and the C-curve magnetic trip handles moderate inrush from motorized or capacitive loads. Breaking capacity is rated 6 kA per EN 60898 and 10 kA per IEC 60947-2, giving the panel designer selectivity headroom for most commercial and light industrial distribution boards.
Ratings that matter for fit
Rated current is 20 A at 30 °C, derated to 18.8 A at 40 °C and 16.2 A at 55 °C — the thermal curve matters if the RCBO sits in a crowded enclosure or near a heat source. The C-curve (5–10× In magnetic release) suits mixed resistive-inductive loads like small motors, pumps, and lighting ballasts. Type AC residual current means it detects sinusoidal AC faults only; for pulsed DC or smooth DC fault currents you need Type A or F. The 1P+N switching arrangement breaks the phase and switches the neutral, common for single-phase final circuits in TN and TT systems.
Mounting and integration
Two modular width units (36 mm) snap onto a standard DIN rail. Depth is 77 mm, installation depth 70 mm — check the enclosure door clearance if using a shallow consumer unit. Supply can enter from top or bottom. IP20 with the distribution board installed and conductors connected; not rated for wet or washdown environments. Halogen-free and silicon-free construction matters for high-reliability installations where outgassing could affect contacts or optics.