The Siemens 3RT2045-3AV00 is a SIRIUS S3 power contactor, rated for AC-3 motor switching at 77 A on a 480 V line. That 77 A figure at 480 V is the number that governs motor load fit — it tells you this contactor can handle a 3-phase induction motor drawing that current under full load, in the switching category that covers starting and stopping a running motor (AC-3 per IEC 60947-4-1). The spring-type terminals on the magnet coil mean no screw torque to verify on the coil connection, but the main circuit wiring needs attention: solid conductors from 2.5 to 16 mm² and stranded from 6 to 70 mm². That stranded range is generous — it lets you land a 70 mm² cable for the power circuit without a lug adapter, which saves a panel-building step.
The S3 frame takes 70 mm width, 140 mm height, 152 mm depth. Clearance around the contactor: 10 mm upward and downward, 10 mm to the side, 20 mm forward.
Switching duty and thermal limits
Maximum switching rates: 900 cycles/hour at AC-1 (resistive), 1000 at AC-3 (motor start/run), 400 at AC-2 (slip-ring motors), 300 at AC-4 (plugging/inching). The AC-3e rate also sits at 1000 cycles/hour. Arcing time spans 10 to 20 ms, and the make/break time at AC is 10 to 21 ms.
Auxiliary contact DC ratings — the detail that matters for control circuits
The auxiliary switch carries DC current ratings that are often the trip point for control-circuit fit: 10 A at 24 V, 2 A at 48 V and 60 V, 1 A at 110 V, 0.9 A at 125 V, 0.3 A at 220 V, 3 A at 400 V, 0.8 A at 440 V. The auxiliary contact mechanical life is typical at 10 million operations.