The Siemens 3RT2045-3AF00 is a SIRIUS S3 power contactor rated 77 A at 480 V in AC-3 duty, meaning it handles motor switching up to that current on a 480 V line — the rating that governs real motor starts, not the higher AC-1 resistive figure. Main contacts are configured 10 normally open and 2 normally closed, with an auxiliary switch block already fitted. The coil terminals are spring-type, not screw — a detail that matters if your panel wiring standard expects cage clamps on the control side.
The S3 frame measures 70 mm wide by 140 mm high by 152 mm deep — that depth includes the arcing chamber and auxiliary block overhang, so check clearance behind the panel door.
Operating environment and ratings
The AC-3e maximum switching frequency is 1 000 operating cycles per hour — that is the limit for motor starts under load; AC-4 (plugging/reversing) drops to 300 cycles per hour. Arcing time runs 10 to 20 ms at 50 Hz. Wire sizes accepted: solid 2.5 to 16 mm² on the power path, stranded up to 70 mm², with auxiliary wiring accepting 2x (0.5 to 2.5 mm²) solid or stranded.