What it is and what it does
The Siemens 3UG4822-2AA40 is a SIRIUS current monitoring relay with a digital setting and LCD display, covering a measurable current range of 0.05...10 A. It runs on an 18...30 V DC supply and provides a relative repeat accuracy of 1%, so the trip point stays tight across the range — no fiddling with trimmers to get a repeatable threshold. The relay output is rated for 3 A at 250 V and 400 V at 50/60 Hz, and the auxiliary contacts handle 1 A at 24 V, 0.2 A at 125 V, and 0.1 A at 250 V.
Mounting and wiring fit
The 22.5 mm width and snap-on mounting let it clip onto a standard DIN rail in any position — no drilling, no extra brackets. Spring-loaded terminals on the main current circuit accept 2x (24...16) AWG solid or stranded wire, which covers the common panel wire sizes for control and monitoring circuits. Clearance around the unit: 0 mm upwards, forwards, backwards, downwards, and at the side, so it can be packed tight against other devices without derating for airflow.
Sourcing and lifecycle
It carries IP20 protection (finger-safe terminals) and a pollution degree of 2, which is the usual spec for clean, enclosed control panels. Operating temperature range is -25 to +60 °C, storage and transport -40 to +85 °C — fine for most industrial environments without special climate control.
IO-Link and reset options
IO-Link communication runs at COM2 (38.4 kBaud), so it can report the actual current value and fault status to a master without extra analog wiring. Auto-reset and external reset are both supported, giving flexibility for unattended restart or manual intervention after a fault clears. A start-up delay of 0...999.9 s is configurable, useful for filtering out inrush on motor starts or compressor cycles.