What it is and what the ratings mean for fit
The Siemens SENTRON 5SM3318-6KK is a 2-pole residual current operated circuit breaker (RCCB), Type A, rated for 100 A continuous load and 30 mA residual current sensitivity on a 230 V AC, 50 Hz supply. The 30 mA trip threshold is the standard for personal protection against direct contact in residential and commercial final circuits — it catches leakage currents that could pass through the human body. The 100 A rating sizes it for a main incoming supply or a high-load submain, not a branch circuit. Type A detection means it responds to AC sinusoidal and pulsating DC fault currents, which covers most modern electronic loads like rectifiers and switching power supplies. The 10 kA short-circuit current rating (SCCR) per IEC 61008-1 and EN 60898 is the maximum fault current the device can safely interrupt without welding contacts or rupturing the case. In a typical domestic or light commercial installation the prospective short-circuit current at the point of supply is often below 6 kA, so 10 kA gives comfortable headroom — no need for a current-limiting upstream MCB in most panels. The conditional breaking capacity per EN 60898 is listed at 1 kA when backed by an overcurrent protective device, which is the coordination value for standard domestic back-up fuses or MCBs. The 2-pole design switches both line and neutral. Mounting is on DIN rail (REG), width 2 modular units (36 mm). Depth is 70 mm, height 90 mm. The enclosure rating is IP20 only when installed in a distribution board with all conductors connected — the terminals are not touch-safe exposed. Overvoltage category III means it is rated for fixed installation downstream of the main distribution board, not for outdoor or wet locations. Silicon-free construction is a bonus for applications where silicone outgassing can contaminate contacts or optical surfaces, such as paint shops or clean-room adjacent panels.
Panel integration and deployment context
The 70 mm installation depth matches the standard SENTRON distribution board depth — no need for a deeper enclosure. The 36 mm width (2 MW) means it occupies two adjacent slots on the DIN rail; plan the rail layout accordingly if you are populating a pre-drilled gland plate with fixed knockouts. Supplementary devices (auxiliary switches, shunt trips, undervoltage releases) can be added on the right side via the modular add-on system. Mechanical service life is 10 000 operating cycles. The instantaneous design trips on the first half-cycle of a residual fault.