The Siemens 5SU1656-0KV40 is a combined residual current device and miniature circuit breaker (RCBO) in a single 1+N-pole module. It integrates a Type AC RCD rated at 300 mA residual sensitivity with a B-curve MCB rated at 40 A, all in a 70 mm deep enclosure. The 6 kA breaking capacity covers the majority of domestic and light commercial final subcircuits where the prospective fault current stays under that threshold.
What the ratings mean for the panel
The 300 mA IΔn is a fire-protection level, not a person-protection level — 30 mA is the touch-safe threshold per IEC 60364. This unit goes into circuits where nuisance tripping from normal leakage (long cable runs, IT equipment) would be unacceptable, but where earth-fault fire risk still needs covering. The B-curve (3–5 In magnetic trip) is standard for resistive and general-purpose loads; it avoids nuisance trips from small inrush that a C-curve would ignore. The 6 kA Icn at 230/400 V is the short-circuit capacity the device can safely interrupt — adequate for TN and TT systems with upstream overcurrent protection sized to keep let-through energy within the device's limits.
Integration note
The 70 mm depth is a key fit dimension for shallow enclosures — many standard RCBOs run 75–80 mm deep, so this unit buys an extra 5–10 mm of wiring space behind the DIN rail. The 1+N-pole format (switched phase, solid neutral) is the common European residential/commercial configuration. Terminal capacity and wire range are standard for the class; verify against your gland-plate and busbar layout before committing the panel layout.