What this RCCB is and where it fits
The Siemens 5SM3646-8KL is a 4-pole residual current circuit breaker (RCCB) from the SENTRON 5SM3 series, designed for selective (time-delayed) tripping on Type A fault currents. It is rated 63 A at 400 V AC, 50 Hz, with a 300 mA tripping residual current. The selective design means it coordinates with downstream RCCBs — it holds through short-duration earth faults to let the downstream device clear first, which keeps upstream circuits live on a faulted branch. Mounts on DIN rail (REG), occupies 4 width units (72 mm), and accepts conductors from 1.5 to 25 mm² solid or stranded. The N-left variant positions the neutral on the left side of the device.
Selectivity and fault-current type — what they mean for your panel
Selective (time-delayed) RCCBs are the backbone of graded earth-fault protection in distribution boards. The 5SM3646-8KL is designed to delay its trip long enough for a downstream non-selective RCCB to clear a fault first — typically up to several hundred milliseconds. This avoids a full-panel blackout when a single branch faults. The Type A classification means it detects sinusoidal AC residual currents plus pulsating DC residual currents, which covers most modern electronic loads (rectifiers, switching power supplies, VFDs). If your installation has three-phase rectifiers or single-phase electronics, Type A is the minimum required by IEC 60364. The 300 mA tripping threshold is typical for fire protection or sub-distribution where nuisance tripping from leakage currents must be avoided — it is not for direct personal shock protection (30 mA is the standard for that).
Mounting and wiring notes
Mounts on DIN rail in any position. Installation depth is 70 mm; overall depth is 77 mm. The supply cord can enter from top or bottom. Terminals accept solid or stranded copper from 1.5 to 25 mm². Tightening torque is 2.5 to 3 N·m. IP20 rated with connected conductors — suitable for enclosed distribution boards. Overvoltage category III. Finger and back-of-hand safe per the protection against electrical shock classification. Silicon-free construction.