What it is and what it does
The Siemens 3RB2036-1QX1 is a SIRIUS solid-state overload relay — it protects three-phase motor circuits against overload and phase failure by monitoring current through straight-through transformers and tripping the contactor when the thermal model exceeds the CLASS 10E curve. CLASS 10E means the relay will trip within 10 seconds at 7.2× the set current, which is the standard protection for standard induction motors starting direct-on-line or star-delta — fast enough to prevent winding damage but tolerant of normal starting inrush. It carries PTB 06 ATEX 3001 Ex II (2) GD certification, so it can be used in Zone 22 dust atmospheres and Zone 2 gas atmospheres when paired with an appropriate contactor — the relay itself is mounted outside the hazardous area but protects motors inside it.
Mounting and wiring
This relay is designed for stand-alone installation — it does not clip directly onto a contactor, so you mount it separately on the DIN rail and wire it to the contactor's control circuit. Dimensions are 55 mm wide, 92 mm high, and 109 mm deep — it takes up a standard 55 mm DIN-rail slot, and the 109 mm depth means it will clear most enclosure back panels without issue. Mounting position is any orientation, and clearance requirements are minimal: 0 mm upwards, forwards, backwards, and downwards, with only 6 mm needed at the sides — so you can pack it tight against other devices. The auxiliary and control circuit uses spring-loaded terminals (push-in type), accepting 2x (0.25... 1.5 mm²) solid or 2x (0.25... 1.5 mm²) finely stranded with ferrule, or 2x (24... 16) AWG — no screwdriver needed for the control wiring.
Auxiliary contact ratings and electrical environment
The relay has one normally-closed (NC) auxiliary contact and zero changeover (CO) contacts — the NC contact is the trip signal that opens the contactor coil circuit on overload. That NC contact is rated for switching: 2 A at 24 V, 4 A at 120 V, 3 A at 230 V, and also 0.55 A at 60 V, 0.3 A at 110 V, 0.3 A at 125 V, 0.11 A at 220 V — these are the maximum continuous currents at those voltages, so match your contactor coil draw against the appropriate row. Power dissipation per pole is 0.02 W — negligible heat, so no derating needed in a crowded panel even at elevated ambient temperatures. Surge voltage resistance is rated at 6 kV, and it withstands 2 kV burst on power ports and 1 kV on signal ports per IEC 61000-4-4, severity level 3 — solid immunity for industrial environments with contactors and drives nearby. Shock resistance is 15g for 11 ms, and it operates in -25 to +60 °C ambient with 100 % relative humidity — fine for unheated machine enclosures and washdown areas as long as the enclosure itself keeps direct spray off the relay.
Lifecycle and sourcing
RoHS compliance date is July 1, 2006, meaning it meets the original RoHS directive; REACH and ATEX documentation are available from Siemens. The IEC 81346-2 reference code is F, which designates it as a protective device in the standard functional naming scheme — useful for panel documentation and BOM consistency.