What the ratings mean for fit
The Siemens 5SY7440-8 is a 4-pole SENTRON miniature circuit breaker with a D tripping characteristic, rated 40 A at 400 V AC. The D-curve means it tolerates high inrush currents — typically 10 to 20 times the rated current for a short period — so it's sized for motor, transformer, or welding equipment branch circuits where the startup surge would trip a B or C curve breaker. On the interrupting side, it's rated 15 kA per EN 60898 and 20 kA per IEC 60947-2; the higher figure applies when the breaker is used as an industrial circuit breaker under the product standard, not just a residential MCB. That 20 kA SCCR at 400 V means it can clear a fault up to 20,000 amps without welding its contacts or cascading failure upstream — important for panelboards with high available fault current. The 4-pole configuration (4P) switches all three phases plus the neutral, but note the neutral is not switched internally — the breaker's product function explicitly states no neutral conductor switching. That means the neutral pole is a solid through-bar or a switched pole that doesn't open the neutral under fault; confirm your circuit design expects a solid neutral path. The breaker occupies 4 width units (72 mm) on a DIN rail, with a total depth of 76 mm and an installation depth of 70 mm behind the panel surface. Mounting position is unrestricted, and the quick assembly system means it snaps onto the rail without tools.
Deployment and environment
Rated for mechanical engineering and industrial environments, the 5SY7440-8 carries pollution degree 3 and overvoltage category III — that's the standard for fixed-installation distribution panels where transient overvoltages from the mains are expected. The operating temperature range spans -40 °C to 75 °C, with a derating curve above 55 °C: the breaker can handle up to 95 % relative humidity at 55 °C, tapering to 35 % at 75 °C. The IP20 rating (with connected conductors) means it's protected against finger contact but not against water ingress — it belongs inside a sealed enclosure, not exposed to washdown. Halogen-free and silicon-free construction matters for environments where outgassing could contaminate optics or sensitive electronics, such as clean rooms or semiconductor fab support areas. The breaker is sealable, which allows a panel builder or inspector to lock the toggle in the ON or OFF position with a padlock — useful for lockout/tagout procedures during maintenance. Touch protection is built into the terminals, so live parts are not accessible when the breaker is installed in a panel with the cover closed.
Compliance and documentation
The breaker is designed and tested to EN 60898 (for residential and similar installations) and IEC 60947-2 (for industrial applications). The UL/CSA listing is at 5 kA per UL 1077 and CSA C22.2 No. 235, which covers supplementary protectors for North American panels. For DC circuits, the breaker is rated 72 V maximum with a 15 kA interrupting capacity per IEC 60947-2. The product designation follows DIN EN 61346-2 and DIN EN 81346-2 letter code F (protective device). Compliance documentation — RoHS, REACH, CE, UKCA, and the manufacturer's declaration of conformity — is available upon request as part of the standard technical documentation package for this SENTRON series.