RCBO for single-phase final circuits
The Siemens 5SU1356-7KK40 is a SENTRON RCBO combining overcurrent protection and residual current detection in a single 2-module-wide (36 mm) package. It protects a single-phase (1P+N) circuit with a Type C tripping characteristic — the magnetic release trips between 5 and 10 times In, so it handles motor inrush and lighting ballast start-up without nuisance trips on a 40 A rated load at 30 °C ambient. Breaking capacity is 6 kA per EN 60898 for domestic/commercial distribution boards, and 10 kA per IEC 60947-2 for industrial panel applications — the higher figure gives headroom on fault-current duty in an MCC or sub-distribution board. The part is instantaneous design (no intentional time delay), so it clears high-impedance earth faults fast. Rated insulation voltage (Ui) is 264 V, overvoltage category III, pollution degree 2 — standard for fixed-installation final circuits in building and light industrial distribution. Supply frequency is 50 Hz only; not suitable for 60 Hz networks.
Thermal derating and mounting
The 40 A rating holds only at 30 °C. At 40 °C derate to 37.6 A, at 50 °C to 34.8 A, and at 70 °C to 29.2 A. If the panel ambient runs hot — say a crowded enclosure with drives — size the upstream protection for the derated figure, not the nameplate 40 A. Mounting position is any, and the supply can enter from top or bottom — no orientation restrictions for the residual-current electronics. Installation depth is 70 mm plus conductor bending space; the overall depth of 77 mm includes the front projection. IP20 only, and that assumes the distribution board is closed and conductors are connected. The 2-module (36 mm) width matches standard DIN-rail cutouts. Halogen-free and silicon-free construction — important for environments where outgassing can contaminate contacts or optics.