RCD unit for selective earth-fault protection
The Siemens SENTRON 5SM2645-2 is a 4-pole selective residual current device (RCD) rated 63 A at 400 V AC, 50 Hz, with a fixed trip threshold of 300 mA, type AC. Selective design means it delays tripping to coordinate with downstream RCDs — only the faulted branch clears, keeping the rest of the distribution board live. Per the datasheet, it occupies 3 modular width units (roughly 54 mm) on a DIN rail and mounts in any position.
What the ratings mean for the panel
The 300 mA rated fault current is not adjustable, and the OFF-delay time is fixed — this is intentional for the selective role: it sits at the supply side of a sub-distribution board, coordinating with 30 mA RCDs downstream. Type AC means it detects sinusoidal AC residual currents only; if the installation includes non-sinusoidal waveforms (rectifiers, VFDs), a type A or B RCD would be required. The 4-pole design switches all three phases plus neutral, so it suits a 3-phase 4-wire system (TN-S or TN-C-S). Insulation voltage is rated 460 V, overvoltage category III, pollution degree 2 — standard for fixed-installation distribution boards in commercial and industrial buildings. Surge voltage withstand is 4 kV, which matches the impulse voltage expected at the service entrance of a building. The operating temperature range spans -40 °C to 75 °C, so the unit can be installed in unheated enclosures or near heat-generating equipment, provided the ambient inside the enclosure stays within those limits. Mechanical service life is 10 000 operating cycles typical — this is a switching device, not a continuous-duty contactor, so the cycle count governs manual test operations and fault-clearing events, not daily switching. Per-pole power loss at rated current in hot state is 3 W, which contributes to the thermal budget inside the enclosure; for a 4-pole unit that totals 12 W dissipation.
Mounting and integration
The 5SM2645-2 snaps onto a DIN rail (fastening method REG) and requires 70 mm installation depth behind the panel door. IP20 is the protection class with conductors connected and the distribution board installed — meaning the front face is touch-safe, but the unit is not sealed against moisture or dust ingress. Supply can enter from top or bottom; the unit is not sealable (no provision for a lead seal on the adjustment cover).