What it is and where it lands
The Siemens 3RV5902-1AP0 is a SIRIUS undervoltage release — a bolt-on accessory for motor circuit breakers. It sits on the breaker's side, wired in series with the control supply, and drops the main contacts the instant its coil voltage falls below the dropout threshold. Rated for 230 V at 50 Hz and 240 V at 60 Hz, AC control supply only. The 50/60 Hz dual-frequency rating means it works on either grid without a jumper change — one part number covers both common line frequencies. Insulation voltage is 690 V with pollution degree 3, which is the standard industrial panel environment (conductive pollution, occasional condensation).
Breaker fit and panel integration
This release fits S00, S0, S2, and S3 frame sizes of the 3RV2 motor circuit breaker series. That's the full range from the compact S00 (up to about 16 A motor protection) up through the S3 (around 100 A). The screw connection terminals match the breaker's own terminal style — same screwdriver tip, same torque range. Snap-on mounting onto 35 mm DIN rail per EN 60715; no tools needed to attach it to the breaker, but the screw terminals need a Pozidriv size 2. Width is 18.5 mm, depth 68 mm, height 90 mm. It's a narrow add-on — doesn't push the breaker outside its standard mounting footprint. The front is finger-safe to IP20 per IEC 60529, so it meets the touch-protection requirement for accessible panel fronts without needing a separate cover.
What the ratings mean for the buyer
The 230/240 V AC rating is the coil operating voltage, not a main circuit rating. It's the voltage that keeps the release picked up. Dropout happens somewhere below about 0.7 × rated — so at 230 V nominal, the release drops the breaker if the control voltage sags below roughly 160 V. That's the undervoltage protection function: it doesn't trip on a momentary blip, but it does clear the breaker on a sustained brownout or loss of control power. Operating temperature range is -20 to +60 °C, storage -50 to +80 °C. The storage range is wider because the part isn't dissipating heat when boxed. In a panel, keep ambient below 60 °C or derate per the thermal curve. The -20 °C floor means it's fine for unheated electrical rooms in most climates, but not for freezer or arctic outdoor applications without a heater.