What it is and what it does
The Siemens 3RU2146-4KD1 is a SIRIUS thermal overload relay — the part that sits between a contactor and the motor, watching for current imbalance and overload. It's a CLASS 10 device, meaning it trips within 10 seconds at 7.2× the set current, which is the standard for standard-duty induction motors driving pumps, fans, and conveyors. Rated for motor loads up to 37 kW at 400 V, 45 kW at 500 V, and 55 kW at 690 V, it covers the common European and North American voltage bands. The auxiliary contact block is integrated — no add-on module needed for the N/C and N/O signals back to the PLC or safety circuit. The auxiliary contacts are rated 2 A at 24 V and 230 V, 3 A at 120 V, and 1 A at 400 V — enough to drive a standard PLC input or a small relay coil. The "for message Tripped" note on the nameplate means the N/C contact opens on a trip, giving a positive signal to the control system.
Where it goes and how it mounts
This is an S3 frame overload relay, the largest in the SIRIUS 3RU2 series. It's designed for stand-alone installation — no DIN rail required, though it can be mounted directly to the contactor or on a mounting plate. The screw terminals on the main circuit accept solid conductors from 2.5 mm² up to 70 mm² stranded, so it handles the heavy power feeds from a 55 kW motor without needing terminal adapters. Mounting position is any orientation, which helps when you're squeezing it into a crowded panel. The auxiliary contact wiring uses smaller terminals (0.5 to 2.5 mm² solid or stranded). Depth is 140 mm, width 70 mm, height 120 mm — plan your gland plate and door clearance accordingly.
Lifecycle and sourcing
Compliance documentation is in order: RoHS compliant per the 03/01/2017 substance prohibition date. The relay carries a 690 V rated insulation voltage and is tested for AC-3e switching up to 1,000 V, so it meets the IEC 60947-4-1 standard for motor starters.
What the ratings mean for your panel
The 37 kW at 400 V rating is the AC-3 (squirrel-cage motor starting) value — that's the real-world number for sizing. The 65 A at 480 V and 62 A at 600 V ratings let you use it on 480 V North American systems without derating. Per-pole power dissipation is 6.3 W, so factor that into your panel thermal budget if you're running multiple relays in a sealed enclosure. Temperature compensation is active from -40 to +60 °C, which covers most industrial environments. Storage range is -55 to +80 °C. The auxiliary switch is integrated — no separate head to order, which saves a line item on the BOM.