77 A at 480 V — motor switching ceiling for US 480 V line
The Siemens 3RT2045-3AB00 is a SIRIUS S3 power contactor rated 77 A at 480 V, which sets the motor full-load current ceiling for a 480 V three-phase feeder. The AC-3 duty cycle maxes at 1 000 switching cycles per hour — that is the limit for repetitive motor starting under load. For AC-4 (plugging/inching) the ceiling drops to 300 cycles/h, reflecting the higher contact wear from breaking locked-rotor current.
Panel fit and wiring — S3 frame, 70 mm wide, 6…70 mm² stranded
The S3 frame measures 70 mm wide × 140 mm high × 152 mm deep. Main power terminals accept stranded wire from 6 mm² up to 70 mm², covering motor feeders from about 10 AWG through 2/0 AWG. The coil connection uses spring-type terminals — no screw tightening needed on the control circuit, which saves time on multi-contactor panels.
Lifecycle and compliance — active production, no obsolescence watch
The -25 °C lower limit is typical for industrial enclosures in unheated spaces; the +60 °C ceiling covers most panel internal temperatures below the breaker trip curve derating threshold. The contactor includes an auxiliary switch — a built-in NO/NC set for feedback to the PLC or holding circuit, eliminating a separate aux block on a basic motor starter.