What this part is and what it does
The Siemens 3VA1112-1AA42-0HH0 is a SENTRON switch disconnector in an MCCB-style housing — IEC frame 160, 4-pole, rated for 125 A continuous across the full ambient range from 40 °C to 70 °C. It provides no overload or short-circuit protection; its job is safe isolation and disconnection under load. The shunt trip release (STL) accepts 12–30 V DC or 24 V AC 50/60 Hz for remote tripping, and the auxiliary switch block carries 2 HQ auxiliary switches plus 1 trip alarm switch, giving 3 CO contacts total.
What the 125 A rating means for panel fit
The 125 A rating is flat from 40 °C to 70 °C — no derating curve to manage in a warm enclosure. That makes it a straightforward drop-in for a 125 A feeder or branch disconnect where the load current is known and stable. The front terminals accept busbar connections, so it integrates into a panel bus system without lug adapters. At 70 mm deep, 101.6 mm wide, and 130 mm tall, it occupies the same footprint as a 3VA1 MCCB of the same frame; the 4-pole width is wider than the 3-pole sibling (76.2 mm).