The Siemens 5SU9356-7KM20 is a SENTRON RCD-operated circuit breaker — an RCBO combining overcurrent protection and residual current detection in a single 2-module (36 mm wide) package. It is rated 20 A with a C tripping curve and Type A fault current sensitivity, meaning it protects against sinusoidal AC and pulsating DC residual currents, which covers most single-phase electronic loads like switched-mode power supplies and variable-speed drives. Breaking capacity is 6 kA per EN 60898 for domestic-type installations and 10 kA per IEC 60947-2 for industrial panel duty — the higher figure is the one to use when coordinating with upstream MCCBs in a distribution board. The 1P+N pole configuration switches the phase and monitors the neutral; the protected pole count is 1.
Thermal derating and conductor sizing
Current rating is temperature-dependent: 20 A at 30 °C ambient, derating to 18.8 A at 40 °C, 18.2 A at 45 °C, 17.4 A at 50 °C, and 16.2 A at 55 °C. If the panel ambient runs above 30 °C, size the downstream load for the derated value, not the nameplate 20 A. The maximum power loss is 1.5 W. Terminals accept solid or stranded conductors from 0.75 mm² up to 35 mm² — enough for the full 20 A circuit plus voltage drop margin on longer runs. Installation depth is 70 mm; overall depth including terminals is 77 mm. Mounting position is unrestricted, and supply can enter from top or bottom.
Environmental and compliance
Halogen-free and silicon-free construction, rated IP20 with conductors connected and the distribution board installed. Ambient operating range is -25 °C to +45 °C; storage range is -40 °C to +75 °C. Overvoltage category III, energy limiting class 3. Touch protection is fitted as standard.