The Siemens 5SU9156-7VK40 is a 2-pole (1P+N) RCBO from the SENTRON 5SU9 series — a combined overcurrent and residual-current device that fits a single 36 mm wide module (2 width units) on a DIN rail. It protects a 40 A final circuit with a C-curve magnetic trip for motor or lighting inrush and a 30 mA Type A RCD element that catches pulsating DC fault currents from electronics or variable-speed drives.
Rated current derates with ambient temperature: 40 A at 30 °C, 37.6 A at 40 °C, 36.4 A at 45 °C, 34.8 A at 50 °C, 32.4 A at 55 °C. If the panel runs at 40 °C ambient, the usable load drops to 37.6 A — a 40 A breaker on a 40 A continuous load would nuisance-trip. Terminals accept solid or stranded copper from 0.75 mm² up to 35 mm², which covers everything from a 1.5 mm² lighting circuit to a 10 mm² feeder. The 77 mm depth plus 70 mm installation depth means it clears a standard 100 mm deep enclosure back wall with room for wiring fingers.
Deployment context
Mounts on a DIN rail in any orientation — vertical, horizontal, upside-down — which simplifies layout in a tight enclosure. The IP20 rating applies only when the distribution board is installed and conductors are connected; the device itself is not sealed for washdown or outdoor use. Type A RCD detects sinusoidal AC faults plus pulsating DC up to 6 mA smooth DC superimposed — critical for circuits with half-wave rectifiers, switch-mode power supplies, or VFDs that can blind a standard AC-only RCD. If the downstream load includes a single-phase drive or LED driver, Type A is the minimum for code compliance in most jurisdictions.