RCCB, 80 A, 300 mA, 4-pole — panel fit and sourcing note
The Siemens 5SM3647-0KL is a SENTRON residual current circuit breaker (RCCB), 4-pole, type AC, with an 80 A rated current and a 300 mA residual trip threshold at 400 V AC. The 300 mA trip level is sized for general distribution protection — it catches earth faults without nuisance-tripping on normal leakage from connected equipment. Type AC means it detects sinusoidal AC residual currents only; not for pulsed DC or smooth DC fault types. Instantaneous design (no intentional delay) means it trips within the RCCB standard response window — suitable for direct fault isolation, not selectivity grading against downstream RCBOs. The N-left terminal arrangement matches the panel busbar layout where the neutral bus runs on the left side of the DIN rail; verify your enclosure's neutral bar position before committing the BOM line. Mounts on standard DIN rail (REG) in any orientation, occupies 4 width units (approx. 72 mm), and has an installation depth of 70 mm. The IP20 rating applies once the distribution board cover is installed with conductors connected — it is not a standalone IP20 part. Terminal range accepts 1.5 mm² to 25 mm² solid or stranded copper, which covers most submain and feeder cable sizes in commercial and light industrial panels.
Mechanical and compliance details
Rated for 10 000 mechanical switching cycles typical, which is the standard endurance for a DIN-rail RCCB in distribution duty — not a high-cycle motor-switching device. Silicon-free construction matters for automotive paint-shop and coating-line installations where silicone outgassing can cause adhesion defects. Overvoltage category III confirms it is rated for fixed installation downstream of the utility meter, not for equipment-level surge protection. Finger and back-of-hand safe touch protection means the terminals are designed to prevent accidental contact during wiring — this is a standard requirement for distribution boards accessible to non-skilled personnel. Supply connection can be top or bottom, which simplifies busbar and cable routing in crowded enclosures.
What the 300 mA trip means in practice
A 300 mA RCCB is not a personnel-protection device — that role is served by 30 mA units. The 300 mA threshold is typically used for fire protection and equipment protection in circuits where some continuous leakage is expected (long cable runs, industrial heaters, or IT equipment with filters). It will not trip on the normal capacitive leakage of a well-designed panel, but it will clear a hard phase-to-ground fault before the upstream overcurrent device operates, provided the fault current exceeds 300 mA.