Switch disconnector for isolation duty
The Siemens 3VA1112-1AA42-0BA0 is a SENTRON 3VA1 switch disconnector in the IEC frame 160 — a 4-pole, 125 A rated continuous current (Iu) device designed for load-break isolation rather than overcurrent protection. It carries no overload or short-circuit release; its job is to safely disconnect a circuit under load, providing visible isolation for maintenance or emergency switching. The 125 A rating on the front means it handles continuous motor or distribution loads up to that current without derating at 40 °C ambient.
Undervoltage release and control voltage
This unit ships with an undervoltage release (UVR) wired for 24 V DC. The UVR trips the disconnector when control voltage drops below the dropout threshold — a standard safety interlock for emergency-stop chains or undervoltage protection schemes. The leading contact is absent, so the UVR does not pre-charge before the main contacts close; sequence logic must come from the external control circuit. The 24 V DC coil is common across panel builds, but verify polarity and free-wheel diode placement if driving from a PLC output or relay.
Electrical ratings and voltage class
Rated insulation voltage (Ui) is 800 V, and maximum operational voltage reaches 690 V AC (50/60 Hz) or 600 V DC. That covers 400/480 V three-phase distribution and most 500–600 V DC bus applications. The 38 W maximum power loss at full load is heat that must be dissipated inside the enclosure — factor it into panel thermal calculations, especially in a sealed IP-rated cabinet.
Mounting and connection
Front-terminal busbar connection is standard; the 101.6 mm width and 70 mm depth fit the 3VA1 frame footprint. The IP40 front protection means the operator face is protected against solid objects over 1 mm, but the enclosure must provide the overall IP rating. The nut keeper kit is included for secure busbar fastening — a detail that saves time during panel assembly.