What it is — and what the ratings mean
The Siemens 3VA2340-5HL42-0JA0 is a SENTRON molded case circuit breaker (MCCB) — the big-frame line-protection version, rated for 400 A continuous current (Iu) through 4 poles. That 400 A holds flat from 40 °C up to 50 °C; above that it derates: 385 A at 55 °C, 370 A at 60 °C, 355 A at 65 °C, 340 A at 70 °C. So if your panel runs hot, you lose headroom fast — plan the enclosure ventilation around the 40 °C baseline. Breaking capacity steps with system voltage: 187 kA at 240 V, 121 kA at 415 V and 440 V, 75.6 kA at 500 V, 17 kA at 690 V. Those are the short-circuit ratings — the part will safely interrupt a fault up to those levels without welding or cascading into upstream gear. For a 400 A frame, that 187 kA at 240 V is substantial; it handles high-fault utility feeds or transformer secondaries. The overcurrent release is an ETU320 electronic trip unit — adjustable, not fixed-thermal, so you can dial in the long-time, short-time, and instantaneous pickup curves to coordinate with downstream breakers. No auxiliary contacts, no undervoltage release, no communication module on this variant. It ships with a shunt trip (STL) for remote opening. The basic switch core is order code 3VA2340-5HL42-0AA0; the integrated auxiliary trip is 3VA9688-0BL32 — spare parts if you ever need to swap the mechanism.
Panel fit — dimensions and mounting
Dimensions: 248 mm high, 184 mm wide, 110 mm deep. That 184 mm width on a 4-pole MCCB means the DIN-rail footprint is fixed — verify horizontal clearance in the enclosure before cutting the gland plate.