The Siemens 3RB2035-2UB0 is a SIRIUS solid-state overload relay — a CLASS 20E device that provides motor overload and phase-loss protection without the thermal lag of a bimetal strip. It mounts directly onto a contactor, saving DIN-rail space in the panel. The CLASS 20E trip curve means it allows a 20-second cold start at 600% of the full-load current setting before tripping — a good match for standard induction motors driving pumps, fans, or conveyors that don't need the faster CLASS 10 curve. Its ATEX certification (PTB 06 ATEX 3001 Ex II (2) GD) qualifies it for use in Zone 22 dust atmospheres and Zone 2 gas atmospheres when paired with an appropriate contactor and enclosure — a detail that matters for grain handling, chemical blending, or any area with combustible dust.
This relay is designed for contactor mounting — it snaps onto the bottom of a SIRIUS contactor, eliminating a separate DIN-rail footprint. The 55 mm width and 92 mm height match the contactor envelope; the 109 mm depth accounts for the relay body extending below the contactor. Screw-type terminals on the main current circuit accept 1 to 35 mm² stranded or 2x up to 25 mm² stranded wire; the control circuit (auxiliary contacts) uses 0.5 to 4 mm² solid or 2x 0.5 to 2.5 mm² stranded. Strip and torque per the terminal markings on the device.
The relay provides no built-in auxiliary contacts (0 auxiliary contacts), so all status signaling must come from the contactor's own auxiliary blocks or an external monitoring relay. This is typical for a solid-state overload relay — the trip signal is internal to the contactor coil circuit. For the contactor coil circuit, the relay's internal switching capacity is rated at 2 A at 24 V DC, 4 A at 120 V AC, and 3 A at 230 V AC — these are the maximum currents the relay can interrupt when signaling a trip. Ensure the contactor coil draw stays under these values.