What it is and what it does
The Siemens SENTRON 3VA2340-5HN32-0AE0 is a 3-pole molded case circuit breaker (MCCB) rated for 400 A continuous current at 40 °C, designed for line protection in distribution panels and industrial switchgear. It carries a maximum breaking capacity of 187 kA at 240 VAC, stepping down to 121 kA at 415/440 V, 75.6 kA at 500 V, and 7.5 kA at 690 V — so the short-circuit rating you need depends on the system voltage it's protecting. This is a line-protection MCCB — meaning it's configured for cable and busbar protection, not motor or generator protection. It ships without an undervoltage release, ground-fault monitoring, or communication module, but it does carry four HQ auxiliary switches for status feedback to a PLC or panel indicators.
Thermal derating and panel fit
The 400 A rating holds steady up to 50 °C ambient. Above that, it derates linearly: 385 A at 55 °C, 370 A at 60 °C, 355 A at 65 °C, and 340 A at 70 °C. If your panel runs hot — say a sealed enclosure near a furnace line — size the breaker for the actual ambient, not the nameplate. Physical footprint: 248 mm high, 138 mm wide, 110 mm deep. That's a standard 3-pole MCCB form factor for a 400 A frame — it'll fit most DIN-rail or panel-mount cutouts in a distribution board. Maximum power dissipation is 96 W at rated load, so factor that into your enclosure thermal budget.