The Siemens 3UG3081-1AK20 is a SIRIUS-brand insulation monitor designed for ungrounded AC networks (IT systems). It continuously measures insulation resistance in the range of 1 to 110 kΩ and triggers a 1 CO contact when the resistance drops below a set threshold. The supply voltage is AC 110/230 V at 50/60 Hz, with a wider rated range of 110–400 V AC.
The 110–400 V AC rated supply covers most common panel voltages — 115 V, 230 V, 400 V — without needing a separate control transformer. The 1 CO contact is a single form-C relay output rated for the control circuit; it switches on a resistance drop below 85% of the setpoint (initial value 0.85). Fault storage is enabled by default, meaning the output latches after a fault clears until manually reset — useful for attended panels where you want a persistent alarm until acknowledged. The measurable line frequency covers 50 and 60 Hz, so it works globally on standard mains. IP20 protection means it's for dry indoor cabinets only — no washdown or dust-tight rating.
The 45 mm width (one 9 mm module equivalent) fits tight layouts. Screw-type terminals accept solid or ferruled stranded conductors from 0.75 to 2.5 mm²; tighten to 0.5–0.8 N·m. No removable terminal for auxiliary circuits — wiring is fixed to the housing. Mounting position is any, and clearance distances (0 mm upwards, forwards, backwards, downwards, at the side) allow zero-gap side-by-side placement on the rail.