What this breaker is and what the ratings mean for fit
The Siemens 3VA1340-5EF42-0AA0-ZD00 is a 4-pole IEC frame 400 molded-case circuit breaker from the 3VA1 series, configured for line protection with a TM240 ATAM trip unit. The headline rating is the 55 kA breaking capacity at 415 V (class M), which tells you this breaker can safely interrupt a fault current up to that level without welding its contacts or cascading the fault upstream — critical for panel SCCR compliance when the available fault current at the panelboard is in that range. The In=400 A continuous rating and adjustable overload protection (Ir = 280 A to 400 A) let you match the breaker to the cable or busbar ampacity, not the other way around.
Trip unit and protection profile
The TM240 ATAM is a thermal-magnetic trip unit. The thermal element handles overloads (Ir adjustable 280–400 A), and the magnetic element handles short-circuits (Ii adjustable 5 to 10 x In, so 2000 A to 4000 A). That magnetic adjustment range matters for selectivity with downstream breakers — you can set it high enough to ride through motor inrush without nuisance tripping, but low enough to clear a bolted fault before the upstream device sees it. The N conductor is unprotected on this variant, which is standard for 3-phase loads where the neutral carries only unbalanced current.