What this 4-pole switch disconnector is and where it fits
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. Rated insulation voltage is 800 V, with max operational voltage 690 V AC and 600 V DC. The IP40 front protection means it's fine inside a closed panel — not for washdown or outdoor exposure without an enclosure.
Key ratings and what they mean for fit
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. The 4-pole design means it switches all three phases plus neutral simultaneously, which is required for TN or TT systems where the neutral must be disconnected for safe isolation. 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. Operating temperature range is -25 °C to 70 °C, storage from -40 °C to 80 °C. 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.
Panel integration and wiring
Dimensions: 70 mm deep, 101.6 mm wide, 130 mm tall. The 101.6 mm width is a 4-pole frame — that's about 4 inches, so it takes up four module spaces on a DIN rail or mounting plate. 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 nut keeper kit is included to simplify busbar mounting. 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. No undervoltage release, no communication function, no voltage trigger — this is a pure manual isolator with status feedback, not a smart breaker.