The Siemens SENTRON 5SM3446-6KK01 is a 4-pole residual current circuit breaker (RCCB) rated 63 A at 400 V AC, 50 Hz. It's a Type A short-time delayed design — meaning it detects pulsating DC fault currents and rides through brief inrush events that would trip a standard instantaneous RCCB. That matters when you're protecting circuits with electronic loads like VFDs, UPS systems, or switching power supplies that leak a pulsed DC component to ground. Rated current holds at 63 A up to 45 °C ambient, then derates linearly: 59.22 A at 50 °C, 55.44 A at 55 °C, 51.66 A at 60 °C, 47.88 A at 65 °C, and 44.1 A at 70 °C. Surge current resistance is rated 1 kA; permissible I²t is 70 000 A²s. The short-circuit current rating is listed as 0 kA, which is standard for an RCCB — it relies on an upstream MCB or fuse to clear fault current. Install it downstream of a properly rated overcurrent device.
Snaps onto DIN rail (REG mount). Occupies 4 width units — 72 mm wide, 90 mm tall, 77 mm deep with 70 mm installation depth. That 77 mm depth is the dimension you check against gland-plate clearance or a shallow enclosure back wall. Mounting position is any orientation; feed from top or bottom. Terminals accept solid or stranded copper from 1.5 mm² up to 25 mm² — covers the range from a 2.5 mm² lighting circuit tail up to a 16 mm² feeder for a submain. Protection against electric shock is finger and back-of-hand safe (IP20 touch-safe terminals).
The closest functional peer in the SENTRON family is the 5SY4304-7CV — a 4-pole MCB, not an RCCB. They share the 4-MW DIN footprint and 72 mm width, but the 5SY provides overcurrent protection only. The 5SM3446-6KK01 adds Type A residual current detection and short-time delay. You can't drop one in for the other without rewiring the circuit protection scheme.