The Siemens 5SM3642-0KL is a 4-pole residual current operated circuit breaker (RCCB) from the SENTRON 5SM3 series, rated 25 A at 400 V AC with a 300 mA residual tripping current, type AC (sensitive to sinusoidal AC fault currents only). It is an instantaneous (non-time-delayed) device, meaning it trips without intentional delay on a fault — typical for general-purpose shock protection where selectivity against downstream RCCBs is not required. The N-left variant places the neutral pole on the left side of the unit, matching panel layouts where the neutral bus is run leftmost.
The 300 mA residual sensitivity is a common ground-fault protection level for fire prevention or equipment protection rather than direct personal shock protection (which typically uses 30 mA); it suits circuits where nuisance tripping from leakage on long cable runs or industrial gear must be avoided.
Mounts on DIN rail (REG) in any orientation, occupying 4 width units — 70 mm installation depth. Terminals accept solid or stranded conductors from 1.5 mm² up to 25 mm²; tighten to 2.5–3 N·m. The housing is finger and back-of-hand safe with IP20 protection once the distribution board is installed and conductors are connected.