What it is and what the ratings mean
The 5SM3646-0LB: It is an instantaneous (non-delayed) type, meaning it trips without intentional time delay on a residual fault. That makes it unsuitable for selective coordination with downstream RCDs unless the downstream devices are short-time-delayed or have a lower threshold. The 1 kA surge current resistance (8/20 µs waveform) is standard for this class — it will survive typical lightning-induced transients on a building supply without nuisance tripping or damage.
Panel integration and mounting
Snaps onto DIN rail (REG profile), occupies 4 width units (about 72 mm at 18 mm per unit). Installation depth is 70 mm, which fits standard distribution board enclosures. Mounting position is unrestricted — vertical, horizontal, or inverted all work. The supply can enter from top or bottom, which simplifies busbar and cable routing in a crowded panel. IP20 protection applies once installed with conductors connected — so it is rated for indoor, dry-location use inside a distribution board. The housing is silicon-free, which matters if the panel is in a paint shop or coating line where silicone vapors cause adhesion defects.
Environmental limits and service life
Rated for ambient temperatures from -5 °C to 45 °C during operation. Storage and transport range is wider: -40 °C to 75 °C. The 45 °C maximum operating limit means the breaker is fine in a ventilated panel in most climates, but if the enclosure is in direct sun or next to heat sources, you need to check internal temperature rise. Mechanical service life is 10 000 switching cycles — typical for a main RCCB that sees infrequent operation. The finger and back-of-hand safe protection (per IPXXB) means the terminals are shielded against accidental contact during wiring — a standard safety feature on modern DIN-rail devices.