What it is and what it does
The Siemens SIRIUS 3RU2136-4DB0-ZX95 is a thermal overload relay sized S2, rated 25 A operational current, with Trip Class 10. It mounts directly onto a contactor to protect motor circuits from sustained overcurrents — the Class 10 trip curve means it will open within 10 seconds at 7.2× the set current, which is the standard for standard-duty induction motor starting. The built-in auxiliary switch includes a "Tripped" message contact for remote status feedback to a PLC or indicator lamp.
Key ratings and what they mean for fit
Rated operational current is 25 A at both 480 V and 600 V, so it handles the same load regardless of whether your motor is on a 480 V or 600 V distribution. The operating voltage rating of 690 V covers the main circuit voltage for most industrial motor feeders. The auxiliary contact ratings are given per voltage: 2 A at 24 V, 3 A at 120 V, 2 A at 230 V, 1 A at 400 V — these are the switching capacities for the trip-indication contact, so confirm your control voltage matches one of these curves. The relay is temperature-compensated from -40 °C to +60 °C, meaning the trip point stays accurate across the typical panel ambient range.
Mounting and wiring
Fastening method is contactor mounting — it clips directly onto the matching SIRIUS contactor, no DIN rail required for the relay itself. Main circuit terminals are screw-type, accepting 2× (0.5…1.5 mm²) or 2× (0.75…2.5 mm²) solid or stranded copper, or AWG 18…2 for two conductors. The auxiliary/control circuit also uses screw terminals. Screwdriver shaft diameter 5…6 mm, Pozidriv PZ 2 tip. Mounting position is any, which helps in tight enclosures. Dimensions: 55 mm wide, 90 mm high, 105 mm deep.