The Siemens 5SU9304-0KK40 is a SENTRON RCBO — an RCD-operated circuit breaker combining overcurrent and residual-current protection in one 18 mm-wide module. It's rated 40 A with a B-curve trip characteristic and 30 mA Type AC residual sensitivity, breaking capacity 10 kA per EN 60898 and IEC 60947-2. The 1P+N design protects one live pole while switching the neutral, and the 600 mm pigtail with solid neutral simplifies wiring in distribution boards.
What the ratings mean for fit
The 10 kA breaking capacity at 230/240 V AC means this RCBO can safely interrupt fault currents up to 10 kA without welding its contacts or cascading failure upstream — standard for residential and light commercial distribution boards where the prospective short-circuit current stays under that threshold. The B-curve (3-5 In magnetic trip) is the default for general-purpose socket circuits and lighting; it avoids nuisance tripping from inrush on resistive loads while still clearing fast on hard shorts. At 18 mm width (1 modular unit), it occupies one DIN-rail position — critical when backfilling an existing board where every slot counts. The 77 mm depth and 70 mm installation depth mean it sits flush in standard distribution enclosures without protruding past the gland plate. The 30 mA Type AC residual sensitivity catches sinusoidal AC earth faults — the most common type in domestic and office wiring. It's not suitable for pulsating DC or smooth DC fault currents (Type A or F would be needed for EV chargers, VFD-fed circuits, or three-phase rectifier loads).
Panel integration notes
Mounts in any position on standard DIN rail. The 1 MW width occupies one position. Supply can enter from top or bottom. IP20 rating applies only when installed in a distribution board with connected conductors — not for open-panel use. The -40 °C to +75 °C ambient range covers unheated utility rooms and outdoor enclosures in temperate climates.