The Siemens 3RT1045-3AD20 is a SIRIUS S3 power contactor rated for motor switching at 45 kW on a 500 V AC-3 supply. AC-3 duty at 1,000 operating cycles per hour; mechanical life of 10,000,000 operations typical.
The headline motor rating is 45 kW at 500 V AC-3 (50 Hz). At 690 V AC-3 the rating drops to 21.1 kW — this is the standard derating for higher voltage motor switching. If your line runs at 400 V, the contactor is rated for 3 A in AC-1 resistive duty, but the motor (AC-3) rating at 400 V is not explicitly stated in the available data; the 500 V figure is the one to use for sizing at that voltage. The coil operates at 50/60 Hz with a voltage tolerance of 0.8 to 1.1 times rated value at 50 Hz, and 0.85 to 1.1 at 60 Hz. The rated control supply voltage is 42 V at 50/60 Hz — a common control voltage in some industrial installations, but verify your panel's control transformer output before specifying. Auxiliary contact ratings: 10 A at 24 V, 6 A at 230 V, 3 A at 400 V, and 0.3 A at 220 V DC. The DC switching capability is limited — at 220 V DC only 0.3 A, so inductive DC loads like brake coils or DC valve solenoids need careful checking against the make/break curve.
Wiring and terminal capacity
Screw-type terminals on main circuit accept solid 2x (0.25 to 2.5 mm²), stranded 2x (10 to 50 mm²), and solid/stranded 2x (2.5 to 16 mm²). The contactor is 70 mm wide, 146 mm high, and 139 mm deep.
No official second-source or cross-reference is listed. If you are evaluating the 3RT1044-1FB46 as a potential alternative, note that the 3RT1045-3AD20 is a size S3 frame with a 45 kW rating at 500 V, while the 3RT1044-1FB46 is a different size and rating — verify footprint and electrical ratings before assuming a drop-in replacement.