What this RCCB is and where it fits
The Siemens 5SM3617-8 is a 2-pole residual current circuit breaker (RCCB) from the SENTRON 5SM3 series, rated 80 A at 230 V AC with a 300 mA residual trip threshold. It's a Type A selective design — meaning it's built to discriminate from downstream RCCBs, so only the faulted branch trips and the rest of the distribution board stays live. That selectivity is the whole point: you don't want a ground fault on a lighting circuit taking out the whole panel. The 10 kA short-circuit current rating (SCCR) is the standard for most commercial and light industrial distribution boards in Europe. The 300 mA trip threshold is sized for equipment protection or circuits with high leakage from long cable runs or VFDs. Mounts on a DIN rail (REG), takes 2.5 width units (45 mm of rail space), and accepts conductors from 1.5 to 25 mm² solid or stranded. The terminals torque to 2.5–3 N·m. It's rated for ambient temperatures from -25 to +45 °C and can be stored from -40 to +75 °C. The IP20 rating means it's protected against finger contact but needs to be inside a distribution board or enclosure with connected conductors.
Panel integration notes
The 70 mm depth and 90 mm height are standard for this class of DIN-rail device. Supply can come from top or bottom, which gives flexibility in busbar routing. The 2.5 width units (45 mm) mean it occupies two and a half 18 mm module slots. Plan your rail fill accordingly — it's wider than a standard single-pole MCB but narrower than a 4-pole RCCB. The silicon-free construction is relevant for potting or conformal coating processes in sensitive environments.
How the ratings drive the decision
The 80 A rating is the continuous current it can carry without tripping — sized for a main incoming supply or a large sub-feed. The 300 mA residual trip is selective: it's deliberately slower and higher than downstream 30 mA RCCBs, so a small leakage on a socket circuit trips the local device, not this one. The 5 kA surge current resistance means it can withstand transient overvoltages from switching or lightning without nuisance tripping. Type A detection means it catches both sinusoidal AC fault currents and pulsating DC fault currents — the kind you get from rectifiers, switching power supplies, or single-phase VFDs. That's the minimum type for modern commercial panels where electronics are present. The overvoltage category III rating confirms it's suitable for fixed installation downstream of the main distribution board.