What it is and what it does
The Siemens 5SU9156-7VK50 is a SENTRON RCBO — an RCD-operated circuit breaker that combines overcurrent protection and residual-current detection in a single 2-module (36 mm wide) package. It's rated 50 A at 30 °C with a C-curve trip characteristic, meaning it handles moderate inrush from motor or lighting loads without nuisance tripping, and clears faults fast once current exceeds 5–10× rated. The Type A residual-current element detects pulsating DC fault currents, not just sinusoidal AC — so it covers variable-speed drives, LED drivers, and other electronics that generate half-wave or phase-controlled leakage.
Breaking capacity and derating
Rated breaking capacity is 6 kA per EN 60898 (the domestic / light commercial standard) and 10 kA per IEC 60947-2 (the industrial standard). That dual rating means it's accepted in both residential distribution boards and industrial sub-distribution panels — the 10 kA figure is the one to use for fault-current studies under IEC 60947-2. Current derating is published: 50 A at 30 °C, 47 A at 40 °C, 45.5 A at 45 °C, 43.5 A at 50 °C, 40.5 A at 55 °C. Ambient operating range is -25 to +45 °C; storage range is -40 to +75 °C. Mounting position is any, which simplifies panel layout.
Installation and wiring
Width is 36 mm (2 width units), depth 77 mm, installation depth 70 mm. Terminals accept solid or stranded copper from 0.75 mm² up to 35 mm² — that's a wide range, covering both small control-circuit tails and heavy feeder conductors. Supply can enter from top or bottom. Touch protection is built in. IP20 rating applies when the distribution board is installed with conductors connected. Halogen-free and silicon-free construction. Overvoltage category III, energy limiting class 3.