The Siemens 5SM2645-8 is a SENTRON 5SM2 RC unit — a residual current (RCD) block that clips directly onto a Siemens 5SY miniature circuit breaker. The assembled pair works as a combined residual-current and overcurrent protective device to DIN EN 61009-1, so one device gives both protection against electric shock and earth-fault fire and the line protection of the MCB behind it. This version is Type A: it detects sinusoidal AC residual currents and pulsating DC residual currents, which is the type required for circuits feeding electronic loads. It is 4-pole, rated 63 A at 400 V AC, with a rated residual current of 300 mA. It suits 5SY miniature circuit breakers rated 6–63 A. The unit is selective (time-delayed), so it is intended as the upstream group device and will hold in while a downstream instantaneous RCD clears the fault — this is what keeps a single earth fault from tripping the whole board. Device depth is 70 mm. Supplied by cBallast on quote-to-invoice terms; lead time and freight are quoted per RFQ against the destination Incoterm.