What this 4-pole MCB does on your DIN rail
The Siemens 5SN6440-8CP is a 4-pole miniature circuit breaker from the SENTRON 5SN series, rated 400 VAC at 50 Hz with a C tripping characteristic. Both ratings apply at 400 VAC — you get two SCCR figures from the same hardware, and the one that governs depends on which standard your local code or panel spec follows.
The 6 kA (EN 60898) / 10 kA (IEC 60947-2) split is the single most important spec for panel coordination. EN 60898 is the residential-standard test sequence; IEC 60947-2 is the industrial standard with a higher let-through energy requirement. If your panel label calls out a 10 kA SCCR at 400 V, this breaker meets it — but only under the IEC 60947-2 clause. For a 6 kA requirement under either standard, it clears comfortably. The 4-pole configuration (3P+N or 4P depending on wiring) means it can switch all three phases plus the neutral, which is mandatory for TN-S or TN-C-S systems where the neutral must be disconnected on a multi-pole fault. The 72 VDC maximum rating matters if you are using the breaker in a DC sub-distribution panel — it is not a high-voltage DC breaker, so keep it on the AC side for 110 VDC or higher rails. Terminal capacity up to 35 mm² solid copper means it accepts standard panel feeder sizes without a reducer lug.
The -40 °C to +75 °C ambient range covers unheated electrical rooms, outdoor enclosures in cold climates, and high-heat machine cabinets.