What it is and what it does
The Siemens 3VA1112-1AA36-0DC0 is a SENTRON 3VA1 series switch disconnector built in an MCCB (moulded-case circuit breaker) form factor — meaning it occupies the same panel footprint and DIN-rail mounting as a breaker but provides no overcurrent or short-circuit protection. Its job is load-break isolation: rated continuous current Iu of 125 A through three poles, with a maximum operational voltage of 690 V AC 50/60 Hz or 500 V DC. This is a pure disconnect — no trip unit, no overload or short-circuit release. The 2 kA short-time withstand rating (1 s and 0.5 s) means it can hold closed under a fault current long enough for an upstream protective device to clear, but it relies entirely on that upstream breaker or fuse for fault interruption.
Key ratings and what they mean for your panel
The 125 A continuous rating (Iu) governs the main conductor sizing and buswork — this is the current it can carry indefinitely without exceeding its 70 °C maximum operating ambient. The 800 V rated insulation voltage (Ui) tells you the clearance and creepage distances are designed for 800 V systems, even though the operational voltage is capped at 690 V AC. Front terminal connections accept lug or clamp terminations on the main circuit. The IP40 front protection means tools or fingers won't reach live parts from the front of the panel, but the switch itself is not sealed — it expects a clean, dry enclosure environment. Operating temperature range is -25 °C to +70 °C, with storage from -40 °C to +80 °C. The integrated undervoltage release (UVR) is factory-set for 208-230 V AC 50/60 Hz. When control voltage drops below its dropout threshold, it trips the switch open — a standard safety interlock for motor starters or emergency-stop chains where loss of control power must isolate the load. Two HQ auxiliary switches (form C, 2 CO contacts) report the main contact position back to the PLC or status panel. Maximum power loss at rated current is 38 W — account for this in enclosure thermal calculations, especially in a densely packed panel. Mechanical endurance is 15,000 operations, which is typical for a disconnect in this class: adequate for daily isolation in a production line, not for high-cycle motor starting.
Lifecycle and sourcing reality
The product designation under DIN EN 81346-2 is Q (switch disconnector), which aligns with its function as a load-break isolating device in power distribution schematics.
Panel integration notes
Dimensions are 130 mm height, 76.2 mm width (3-pole), and 70 mm depth — this is the standard 3VA1 frame 160 footprint. Front-terminal arrangement means all power and control wiring lands on the face of the device, so allow clearance for lug wrenches and auxiliary-wire routing. The optional motor-drive extension (listed as available) can be fitted for remote switching without adding panel depth.