The Siemens 3VA1112-1AA42-0AG0 is a SENTRON 3VA1 switch disconnector in MCCB design — IEC frame 160, 4-pole, rated for 125 A continuous current (Iu). It's a pure isolator: no overload or short-circuit protection built in, so it's meant for applications where the upstream device handles fault interruption and this part provides visible isolation and safe disconnection under load. The 4-pole configuration makes it suitable for three-phase plus neutral switching, common in distribution panels feeding mixed single-phase and three-phase loads.
The 125 A rated continuous current (Iu) sets the maximum load it can carry continuously without exceeding temperature limits. That's the number you match to your feeder or load current — not a motor FLA, but the ampacity of the circuit it isolates. It ships with 1 auxiliary switch HP and 1 trip alarm switch HP — that's two CO contacts total. The auxiliary switch signals the open/closed position; the trip alarm switch signals when it's been operated (manually or via the optional motor drive). Useful for remote status indication in a PLC or SCADA system. The optional motor drive allows remote switching, though it's not included here. Power loss is 38 W max at rated current. That's heat that stays inside the enclosure — factor it into your panel thermal calculation, especially if the switchgear is densely packed. The 15 000 mechanical endurance cycles is typical for a switch disconnector in this class — fine for infrequent switching, not for a daily motor start application.
Front terminals for the main circuit with busbar connection type — meaning it's designed to bolt onto a busbar system, not for individual cable lugs. The auxiliary contacts are wired separately via the front terminal block. The 1 auxiliary switch + 1 trip alarm switch HP configuration gives you two independent signal paths — one for position, one for operation event.