What it is and what it does
The Siemens 5SM3646-8KK12 is a 4-pole residual current operated circuit breaker (RCCB) from the SENTRON 5SM3 series, designed as a Type A selective device with a rated tripping residual current of 300 mA and a rated current of 63 A at 400 V AC. The selective design (short-time delayed) means it coordinates with downstream RCCBs — it holds during a fault long enough for the downstream device to clear, isolating only the faulty branch. This avoids a full-panel blackout on a single branch fault. Type A detection covers sinusoidal AC residual currents plus pulsating DC residual currents.
Key ratings and what they mean for fit
Rated at 63 A continuous and 300 mA trip threshold: this is a feeder or submain RCCB, not a final-circuit device. The 300 mA threshold provides earth-leakage protection while tolerating the natural leakage of long cable runs and multiple connected loads. Rated impulse withstand current of 1 kA (surge current resistance) means it survives the inrush from capacitor banks or nearby lightning-induced surges without nuisance tripping — important for industrial panels with power-factor correction or long overhead supply lines. Mechanical service life of 10 000 switching cycles typical — adequate for a protective device that operates infrequently; not a switching contactor for daily cycling.
Mounting and integration
Snap-on DIN rail (REG) mounting, 4 width units (72 mm wide). Mounting position any orientation, installation depth 70 mm. Terminals accept solid or stranded copper from 1.5 mm² up to 25 mm², with a tightening torque of 2.5 to 3 N·m. IP20 with connected conductors in an installed distribution board — standard for enclosed panel mounting, not for wet or outdoor locations without a weatherproof enclosure.
Lifecycle and sourcing reality
This is the SIGRES variant, specified for harsh ambient conditions — the standard 5SM3 RCCB without the SIGRES suffix is the standard-duty version. The SIGRES designation means the internal components and housing are selected for higher resistance to humidity, temperature cycling, and corrosive atmospheres, per the manufacturer's SIGRES specification.