The Siemens 5SU9156-7VK20 is a SENTRON RCBO — an RCD-operated circuit breaker that combines overcurrent protection and residual current detection in a single 2-module (36 mm wide) unit.
Derating that matters for panel builders
The 5SU9156-7VK20 carries a full derating table from 30 °C to 55 °C: 20 A at 30 °C, 18.8 A at 40 °C, 18.2 A at 45 °C, 17.4 A at 50 °C, and 16.2 A at 55 °C. If the distribution board ambient sits at 45 °C — common in a sealed enclosure — the usable continuous current drops to 18.2 A, so a 20 A load would nuisance-trip on a warm day. Plan the branch circuit load at the derated figure, not the label.
That 35 mm² upper end is unusual for a 20 A RCBO — it means the terminals are oversized for the rating, making daisy-chaining or looping through larger feed conductors straightforward. Strip length and torque values follow the standard SENTRON terminal spec; no special crimp lugs needed for the full range.
Mounting and clearance notes
IP20 applies when the distribution board is installed with conductors connected — exposed terminals are touch-protected per the product feature listing.
Halogen-free and silicon-free construction, which matters for installations with sensitive electronics or where low-smoke, zero-halogen cabling is specified. Energy limiting class 3, meaning it limits let-through energy well in a fault condition.