What it is and what it does
The Siemens 5SU9356-1KK40 is a 2-pole (1P+N) SENTRON RCBO — an RCD-operated circuit breaker that combines overcurrent and residual current protection in a single 36 mm wide module. Rated 40 A at 30 °C with a Type C tripping characteristic, it handles the moderate inrush of motor-starting or lighting ballasts without nuisance trips. The 6 kA breaking capacity per EN 60898 covers most domestic and light commercial service-entrance faults; the 10 kA per IEC 60947-2 gives headroom for industrial distribution where fault currents run higher.
Mounting and integration
Snaps onto standard 35 mm DIN rail — 2 modular width units (36 mm) — and accepts supply from either top or bottom, which simplifies busbar routing in crowded enclosures. Depth of 77 mm and an installation depth of 70 mm leave room for wiring behind the DIN rail. Rated IP20 once the distribution board is closed and conductors are connected; not for wet-area panel faces without a cover.
Thermal derating and environment
Full rating is 40 A at 30 °C. Above that, derate linearly: 37.6 A at 40 °C, 36.4 A at 45 °C, 34.8 A at 50 °C, 32.4 A at 55 °C. Ambient range spans -40 °C to 75 °C, and the device is halogen-free and silicon-free — relevant for clean-room or semiconductor-adjacent installs where outgassing matters. Humidity tolerance up to 95%.