The Siemens 5SU1656-1KK40 is a SENTRON 5SU1 series RCBO — a combined residual-current circuit breaker and miniature circuit breaker in one 2-module (36 mm wide) package. It occupies a single DIN-rail position in a distribution board, rated for 40 A at AC with a C tripping characteristic and 6 kA breaking capacity per EN 60898. The 1P+N pole configuration means it switches the phase and monitors the neutral, tripping on AC fault currents only. For panel thermal planning: the unit dissipates up to 15.6 W at rated load, and current must be derated as ambient temperature rises — from 40 A at 30 °C down to 29.2 A at 70 °C. That derating curve is the one that governs real-world fill factor in a sealed enclosure.
The 36 mm width (2 width units) and 70 mm installation depth fit standard SENTRON distribution boards. Terminal capacity accepts solid or stranded conductors from 0.75 mm² up to 35 mm² — sized for the full 40 A circuit without pigtailing.