What the ratings mean for fit
The Siemens 3VA2340-5HN32-0KJ0 is a SENTRON-series molded case circuit breaker (MCCB) designed for line protection in distribution panels. Its 400 A continuous current rating at 40 °C is the headline number for sizing the feeder — this breaker carries that load continuously without tripping on thermal overload. The interrupting capacity tells you the fault it can safely clear: 187 kA at 240 V, stepping down to 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 is high enough for most secondary-side service-entrance applications where available fault current is substantial. The 3-pole construction handles three-phase circuits. A shunt trip (STL) is built in, plus two auxiliary switches and one trip-alarm switch — so remote tripping and status feedback are covered without an add-on module.
Thermal derating and power loss
The 400 A rating holds flat from 40 °C up to 50 °C. Above that, derate linearly: 385 A at 55 °C, 370 A at 60 °C, 355 A at 65 °C, 340 A at 70 °C. If the breaker sits in a warm enclosure — say, a non-ventilated panel near other heat sources — factor that 70 °C ceiling into your load calculation. Maximum power loss is 96 W, which matters for enclosure thermal management when multiple breakers are ganged.
Physical integration and environment
Dimensions are 248 mm high, 138 mm wide, 110 mm deep — a standard MCCB footprint for panel-mount installation on a mounting plate or DIN rail adapter. Operating temperature range is -25 °C to 70 °C; storage range is -40 °C to 80 °C. The breaker includes a trip indicator and a voltage-trigger function, and it ships without ground-fault monitoring or undervoltage release.