What this breaker is and what it does
The Siemens 3VA2340-5KP42-0DA0 is an IEC frame 400 molded-case circuit breaker with a 55 kA interrupting capacity at 415 V — breaking capacity class M, which means it handles medium-level fault currents typical of industrial distribution panels without needing an upstream current-limiting fuse. It's a 4-pole unit, so it switches all three phases plus the neutral, with the neutral protection adjustable from OFF up to 100% of the phase rating. The electronic trip unit is an ETU850 with LSI protection: Long-time (overload) pickup Ir adjustable 160 A to 400 A, Short-time (short-circuit with delay) Isd adjustable 0.6 to 10× In, and Instantaneous Ii adjustable 1.5 to 10× In. That LSI curve gives you selectivity downstream — you can coordinate with feeder breakers so a fault on a branch trips only the branch breaker, not this main. The built-in undervoltage release is rated 208-230 V AC 50/60 Hz, so if control power drops, the breaker opens automatically.
Lifecycle and sourcing reality
The breaker ships with a nut keeper kit included, which is a small detail but saves a trip to the hardware bin during panel assembly. The description also notes an undervoltage release accessory for 3VA1 — that's the release itself, already fitted in this variant, so verify your control voltage matches the 208-230 V AC coil before wiring.
What the ratings mean for fit
The 400 A continuous rating (In) and the 160-400 A overload range (Ir) mean this breaker fits as a main or large feeder in a 400 A panelboard. The 55 kA Icu at 415 V is the maximum short-circuit current it can safely interrupt once — that's the breaking capacity under IEC 60947-2. If your available fault current at the panel is higher than 55 kA, you'd need a current-limiting device upstream or a higher-rated frame. Class M (medium) breaking capacity is the standard choice for most industrial switchboards; class H (high) would be needed for high-fault locations like near a transformer secondary. The 4-pole configuration with adjustable neutral protection is useful for 3-phase + N systems where you want to protect the neutral conductor against overload, common in panels feeding mixed single-phase and three-phase loads. The nut keeper kit is a captive hardware feature that prevents loose nuts falling into live buswork during installation — a practical panel-builder detail.