What this part is and what it does
The Siemens 3VA1112-1AA36-0BA0 is a SENTRON 3VA1 switch disconnector in MCCB design, IEC frame 160, 3-pole, rated 125 A continuous current (Iu). It is a pure disconnecting means — no overload or short-circuit protection built in. The part carries an undervoltage release (UVR) at 24V DC, so it drops the load if control power fails. Rated insulation voltage is 800 V, max AC operational voltage 690 V 50/60 Hz, max DC operational voltage 500 V.
What the ratings mean for fit
The 125 A rating is the continuous current the switch can carry without exceeding temperature limits — it is not a breaking capacity. This is a switch disconnector, not a circuit breaker; it isolates a load under no-load or low-load conditions. The 38 W max power loss at rated current matters for enclosure thermal budgeting, especially in a sealed panel. IP40 on the front means the face is protected against tools and wires over 1 mm, but the body is not sealed against moisture — keep it in a dry enclosure. The undervoltage release (UVR) at 24V DC is wired into the control circuit. If the 24V supply drops below the dropout threshold, the switch trips open — useful for emergency-stop chains or power-loss disconnection where you want automatic isolation on control-power failure. No auxiliary contacts are fitted, so you cannot signal the switch position back to a PLC without adding an external auxiliary switch block.
Panel integration and mounting
The 3VA1 frame is a standard MCCB footprint: 70 mm deep, 76.2 mm wide, 130 mm tall. It mounts on a DIN rail or directly to a backplate via the screw terminals. Front terminal connection for the main circuit — lug terminals accept cable lugs. The 3-pole unit fits the same cutout as a 3-pole MCCB, so it drops into a panel designed for a 3VA1 breaker without rewiring the bus bars.