What it is and what it does
The Siemens 5SM2827-8 is a SENTRON residual current unit (RC unit) designed for use with the 5SP4 series. It is a 2-pole, type A, selective device rated at 100 A and a tripping fault current of 1000 mA at 230 V AC. The selective design (type S) means it incorporates a short time delay, allowing downstream RCDs to trip first on a ground fault, so only the faulted branch is isolated — the main feeder stays live. This coordination is critical in distribution boards serving multiple sub-circuits.
Key ratings and what they mean for your panel
Rated at 100 A continuous current, this RC unit handles the full load of a main feeder or heavy sub-main. The 1000 mA trip threshold is intentionally high — it prevents nuisance tripping on systems with natural leakage (long cable runs, multiple loads) while still providing earth-fault protection. Type A detection means it responds to sinusoidal AC residual currents and pulsating DC residual currents — the standard for circuits with single-phase rectifiers, switched-mode power supplies, or electronic loads. Type A covers the majority of modern commercial and light industrial panels. Rated insulation voltage is 460 V, overvoltage category III, so it is rated for fixed installation downstream of the main distribution board. The surge current resistance of 5 kA (8/20 µs) means it withstands lightning-induced surges without damage.
Mounting and integration
Snaps onto standard DIN rail (REG) and occupies 4 modular width units. Installation depth is 70 mm. Mounting position is any. Supply connection can be top or bottom. Operating temperature range is -25 °C to +45 °C; storage range extends to -40 °C to +75 °C. Mechanical service life is 10,000 switching cycles typical.