What it is and what it does
The Siemens 3UG4825-1CA40 is a SIRIUS residual current monitoring relay with digital setting, designed for three-phase supplies. It detects ground faults by measuring the vector sum of phase currents via an external summation current transformer (not included). The adjustable trip threshold spans 30 mA to 40 A, covering both sensitive personnel protection and equipment-level leakage detection. The relay operates on a 24 V DC auxiliary supply and provides one changeover output contact rated 3 A at 250 V AC. It includes an error memory function and supports external reset, which is useful for remote reset in unattended panels or for latching until manual acknowledgement.
Where it fits and how to mount it
The 22.5 mm wide housing snaps onto a standard 35 mm DIN rail, with screw and snap-on fastening. Mounting position is any, so it fits in tight panel layouts without derating. Depth is 91 mm, height 102 mm — it occupies one standard modular space and leaves room for adjacent breakers or contactors. The enclosure and terminal blocks are rated IP20, meaning finger-safe but not protected against water ingress. Pollution degree 3 (conductive pollution or dry non-conductive that becomes conductive due to condensation) means it is suited for industrial control panels, not clean-room or sealed environments.
Sourcing and lifecycle posture
The operating temperature range is -25 to +60 °C, with storage and transport tolerance from -40 to +85 °C. This covers most industrial environments from cold warehouses to warm cabinets. The measurable current range extends from 10 mA to 43 A, slightly wider than the adjustable trip band, giving headroom for setting the threshold at the low or high end.