The Siemens 3RB2045-2EW1 is a SIRIUS solid-state overload relay — the device that sits between the contactor and the motor, watching current and tripping on sustained overload before the winding insulation cooks. It's the solid-state version, meaning no bimetal strip to drift or degrade over time; the trip characteristic stays put. Trip class is CLASS 20E, which means it must trip within 20 seconds at 7.2× the full-load current setting. That's the standard choice for standard-start induction motors — pumps, fans, compressors — where the starting transient clears before the relay times out. It's not for high-inertia loads that need a longer Class 30 or 40 curve. The main current circuit uses straight-through transformers, so the motor leads pass through the relay body without looping or wrapping. That simplifies installation in a tight panel — no bending large cable around a CT core.
Hazardous-area and environmental fit
This relay carries PTB 06 ATEX 3001 Ex II (2) GD certification. That 'II (2) GD' means it's approved for installation in the safe area but can protect a motor located in a Zone 1 or Zone 2 gas atmosphere, or Zone 21 or 22 dust atmosphere. Per IEC 60079, the associated apparatus must be Ex-certified for the loop. Confirm the Ex marking on the nameplate before commissioning into a hazardous-area circuit. Front protection is IP20 — finger-safe but not washdown-rated. Mount it inside a panel with a door or cover; it won't survive a hose-down. Relative humidity during operation is rated for 100 % — no de-rating needed for condensation-prone environments, as long as the IP20 front is inside a sealed enclosure.
Mounting position is any orientation — no derating for side or upside-down mounting. That's zero-gap stacking vertically, so you can pack relays tightly in a column. Side clearance of 6 mm is the only air gap needed — useful in a crowded DIN-rail panel. Dimensions are 124 mm deep, 70 mm wide, 106 mm tall. The 70 mm width is standard for SIRIUS 3RB2 form factor — it occupies three 22.5 mm-wide module spaces on the DIN rail. Depth of 124 mm means it will clear a 120 mm-deep enclosure, but verify the door clearance if a disconnect handle or contactor sits in front. Wiring: solid conductors 0.5 to 4 mm², or 2× 0.5 to 2.5 mm² in parallel. Finely stranded with ferrules: 0.5 to 2.5 mm², or 2× 0.5 to 1.5 mm². That covers standard motor leads up to about 4 mm² (roughly 12 AWG). No special lug or ring terminal needed — spring-cage or screw terminals depending on the variant; confirm the termination type on the nameplate.
Compliance documentation: the ATEX certificate (PTB 06 ATEX 3001) is the primary regulatory document. The relay also carries IEC 61000-4-4 burst immunity at severity level 3 (2 kV power ports, 1 kV signal ports) and surge voltage resistance rated at 8 kV. No RoHS or REACH statement is in the evidence; request the manufacturer's declaration if your compliance audit requires it.