The Siemens 5SU1354-4KK20 is a SENTRON RCBO combining overcurrent protection and residual current detection in a single 2-module-width (36 mm) package. It's a 1P+N device with Type F residual current sensitivity — meaning it's designed for circuits where variable-speed drives or other frequency converters might generate smooth DC fault currents or mixed-frequency residuals that a standard Type A would miss. The C characteristic (20 A rated) handles moderate inrush from motor starters or lighting banks without nuisance tripping. Breaking capacity is rated 10 kA per EN 60898 and 20 kA per IEC 60947-2 — the higher figure applies when the device is used as a distribution board component per the manufacturer's instructions. That dual rating gives you flexibility in specifying for different national standards or fault-level requirements at the panel design stage.
Thermal derating and mounting
Full rated current of 20 A holds only up to 30 °C ambient. At 40 °C it's 18.8 A, at 50 °C it's 17.4 A, and at 70 °C it drops to 14.6 A. If this RCBO sits in a crowded enclosure with other heat-generating devices, check the actual ambient around the device — the published derating curve lets you calculate whether you need to upsize the breaker or improve ventilation. Mounting position is unrestricted, and the supply can enter from top or bottom, which simplifies busbar routing in a distribution board. Installation depth is 70 mm, overall depth 77 mm. The IP20 rating applies only when the distribution board is installed and conductors are connected — it's not a standalone ingress protection figure for exposed mounting.
Lifecycle and compliance
Overvoltage category III and pollution degree 2 are standard for fixed-installation distribution boards. The device is classified as energy limitation class 3, which governs let-through energy during a fault — relevant for coordinating with downstream equipment.