40 A B-curve RCBO for final-circuit protection
The Siemens SENTRON 5SU1656-0KK40 is a 1P+N RCBO (residual current operated circuit breaker with integral overcurrent protection) rated 40 A with a B tripping characteristic. It interrupts fault currents up to 6 kA per EN 60898, which covers the majority of domestic and light commercial final circuits where the prospective short-circuit current stays under that threshold. The B curve means magnetic trip occurs at 3–5× In (120–200 A), suited for resistive and general-purpose loads where inrush is modest — lighting, socket outlets, small heaters. For motor or transformer circuits with higher inrush, a C or D curve would be the correct choice. Rated current is 40 A at 30 °C ambient, with a published derating table: 37.6 A at 40 °C, 36.4 A at 45 °C, 34.8 A at 50 °C, 32.4 A at 55 °C, 32.4 A at 60 °C, 30.8 A at 65 °C, and 29.2 A at 70 °C. If the distribution board sits in a warm machine cabinet or near heat sources, use the derated value for continuous load sizing — the 40 A label applies only at 30 °C ambient.
Panel fit and wiring
Two-module width (36 mm) on a standard DIN rail, 77 mm deep, 90 mm tall. Installation depth is 70 mm — verify enclosure depth against the back wall clearance, especially in shallow consumer units. Mounting position any; supply can enter from top or bottom. Wire range accepts 0.75 to 35 mm² solid or stranded, which covers most final-circuit conductors up to 6 AWG. Spring-cage terminals? The spec does not state terminal type, but the wire range is generous for a 40 A device — expect tunnel or screw terminals rated for the full cross-section. IP20 rated when installed in a distribution board with conductors connected — this is the standard for enclosed panel-mount devices, not for open or wet locations. Halogen-free and silicon-free construction, relevant for installations in public buildings or areas with sensitive electronics where outgassing during a fault must be minimized.
Compliance and approvals
Designed to EN 60898 (rated breaking capacity 6 kA), overvoltage category III, energy limiting class 3. The product designation follows DIN EN 61346-2 and DIN EN 81346-2 (function code F). Type of fault current is AC — this RCBO detects sinusoidal AC residual currents only. For pulsed DC or smooth DC fault currents, an A or B type RCD would be required. The manufacturer's standard compliance documentation (RoHS, REACH, CE) applies; specific declarations are available on request.