What this RC unit is and what it does
The Siemens SENTRON 5SM2835-8 is a 3-pole residual current (RC) unit designed for use with the 5SY series miniature circuit breakers. It provides Type A residual current protection with a selective (time-delayed) characteristic, rated at 63 A and a tripping fault current of 1000 mA at 400 V AC, 50 Hz. This means it is built for installations where a delayed trip is needed to achieve selectivity with downstream RCDs, preventing nuisance tripping on the main feeder while still clearing earth faults.
Key ratings and what they mean for fit
The 63 A rating is the thermal continuous current at 40 °C ambient. At higher panel temperatures, the unit derates: 58.6 A at 40 °C, 56.7 A at 50 °C, 54.81 A at 55 °C, 53.55 A at 60 °C, 52.29 A at 65 °C, and 50.4 A at 70 °C. If your panel runs hot, size the upstream breaker for the derated value, not the nominal 63 A. The 1000 mA tripping threshold is high — this is for main feeders or sub-distribution where a lower mA rating would cause coordination issues with downstream 30 mA RCDs. The selective design (short-time delayed) ensures the downstream device trips first on a low-impedance fault. The unit occupies 3 modular width units (each 18 mm wide) on a DIN rail (REG). Mounting position is any orientation. Insulation voltage is rated 460 V, overvoltage category III, suitable for fixed installation in distribution boards. Surge current resistance is 5 kA, and the mechanical service life is 10 000 operating cycles. The unit is silicon-free, which matters for potting or conformal-coating processes in certain industrial environments.
Panel integration notes
Mounts on DIN rail (REG) — standard for distribution boards. Depth is 70 mm, width 107 mm, height 90 mm. The supply cord can enter from top or bottom. Protection class is IP20 once installed in a distribution board with connected conductors. The unit is designed for the 5SY series; verify mechanical compatibility with your specific MCB model if using a different brand.