Rated parameters and breaking capacity
The Siemens SENTRON 5SU1324-7FA40 is a 2-pole RCBO (residual current circuit breaker with overcurrent protection) in the instantaneous design, tripping characteristic C. Rated at 40 A at 30 °C with a rated voltage of 230/240 V AC at 50 Hz, it provides overcurrent and earth-fault protection in a single module. The breaking capacity is 10 kA per EN 60898 and 15 kA per IEC 60947-2 — the higher IEC figure matters when the device is installed in an industrial distribution board where fault levels may exceed the domestic 10 kA threshold. The C-curve (5–10× In) suits moderate inrush loads like small motors or lighting banks, but not high-inrush transformers or drives. The device occupies 3 modular width units (54 mm) on a DIN rail, with a depth of 77 mm and an installation depth of 70 mm. Supply can enter from either top or bottom, and the mounting position is unrestricted. IP20 applies only when the distribution board is installed with conductors connected.
Thermal derating and environmental range
Rated current is 40 A at 30 °C, derating to 29.2 A at 70 °C. The full derating curve is documented: 37.6 A at 40 °C, 36.4 A at 45 °C, 34.8 A at 50 °C, 32.4 A at 55 °C and 60 °C, and 30.8 A at 65 °C. Ambient operating range spans –40 °C to +75 °C. For a panel that sees elevated internal temperatures — typical in a crowded enclosure or near a heat source — use the 40 °C or 50 °C column to size the circuit, not the 30 °C headline figure.
Compliance and approvals
The RCBO is rated for overvoltage category III, pollution degree 2, and carries an energy limitation class of 3. Insulation voltage (Ui) is 264 V, surge voltage resistance is 4 000 V. The minimum test voltage is 195 V. The device is halogen-free and silicon-free, which matters for clean-room or corrosive-environment installations where outgassing must be minimised.