What this 3VA2 carries
The Siemens 3VA2340-5JQ42-0BA0 is a SENTRON molded case circuit breaker (MCCB) designed for line protection in distribution panels. It's a 4-pole unit rated 400 A continuous at 40-50°C, derating to 300 A at 70°C — so the full 400 A holds across typical switchroom ambient, but you lose 100 A if the panel runs hot. Breaking capacity runs 187 kA at 240 VAC, 121 kA at 415/440 V, 75.6 kA at 500 V, and 7.5 kA at 690 V. That 187 kA at 240 V covers high-fault utility feeds; the 7.5 kA at 690 V is the ceiling for industrial 690 V buswork. It ships with an undervoltage release (UVR) fitted and has a communication function onboard — meaning it can talk to a BMS or PLC for remote trip indication and monitoring, without needing an add-on module. The UVR drops the breaker on loss of control voltage, standard for emergency-stop or undervoltage protection schemes.
Sizing and thermal reality
The continuous current rating is 400 A from 40°C through 50°C ambient. At 55°C it's 375 A; at 60°C, 350 A; at 65°C, 325 A; at 70°C, 300 A. If your panel ambient sits at 55°C and you need the full 400 A, you oversize to the next frame. The maximum power loss is 98.5 W — that's the heat this breaker dumps into the enclosure at full load, so factor it into your thermal budget, especially in a sealed or outdoor cabinet. Physical footprint: 248 mm tall, 184 mm wide, 110 mm deep. That's a 4-pole frame in a standard SENTRON 3VA2 size, so it occupies the same panel cutout as other 3VA2 4-pole units. The 110 mm depth means it clears a 120 mm deep enclosure with room for wiring gutters.