What it is and what it does
The Siemens SENTRON 5SU1356-7KK08 is a combination residual current circuit breaker with overcurrent protection (RCBO) — one device that handles both short-circuit and earth-fault protection for a final subcircuit. It's a 1P+N, 2-pole unit rated 8 A with a C-curve tripping characteristic and a 30 mA residual current trip threshold, so it protects a single-phase line against overloads, short circuits (6 kA per EN 60898), and ground faults in one 2-module-width (36 mm) package.
What the ratings mean for fit
The 8 A rating is at 30 °C; at 40 °C it derates to 7.52 A, at 50 °C to 6.96 A, and at 70 °C to 5.84 A. If the panel runs hot, the actual load must stay under the derated figure — the C-curve magnetic trip still holds at 5–10× In for motor-start or lighting inrush, but the thermal element responds to the ambient-adjusted current. The 30 mA residual-current threshold is Type A, meaning it detects pulsating DC fault currents as well as sinusoidal AC — covers most modern electronics and variable-speed drives on the protected circuit. The 6 kA breaking capacity is per EN 60898, adequate for domestic and light commercial distribution boards where the prospective fault current stays under that level. At 2 modular width units (36 mm wide, 77 mm deep, 90 mm high), it snaps onto a DIN rail and fits a standard 18 mm-per-module distribution board. Mounting position is any orientation, and the supply can enter from top or bottom — no special orientation required for the installer.
Where it goes in a panel
This RCBO is designed for a DIN-rail distribution board — residential, commercial, or light industrial sub-distribution. The IP20 rating applies only when the board is installed with connected conductors, so it's not for wet or outdoor locations without an enclosure. Pollution degree 2 (normal, non-conductive) and overvoltage category III (fixed installation) confirm it's a distribution-board component, not a machine-tool or outdoor device.