SIRIUS S3 Power Contactor — 37 kW AC-2, 66 A AC-4
The Siemens 3RT1045-3AP06-ZX95 is a SIRIUS power contactor in frame size S3, rated for 37 kW at 400 V in AC-2 duty (slip-ring motor starting) and 66 A in AC-4 duty (plugging/reversing). It lands on the critical path for any motor control panel where the load demands a contactor that can handle frequent inching or reversing — the AC-4 rating at 66 A tells you it's built for that abuse, not just across-the-line starts. Screw-type terminals on the main circuit accept stranded conductors up to 2x 50 mm² and solid wires 2x 0.25–2.5 mm². That's enough cross-section for the full 66 A AC-4 load without needing lug adapters — one less thing to chase before the outage window closes.
Dimensions: 146 mm high, 90 mm wide, 139 mm deep. IP20 on the front with cover or box terminal; the terminal itself is IP00. In a panel with pollution degree 3 environment, that's expected — the enclosure provides the environmental seal. No washdown rating here; this is a dry-panel part.
Switching Ratings and Mechanical Life
Rated operational current at AC-1: 900 operations per hour maximum; AC-3 (squirrel-cage motor starting): 1,000 ops/h; AC-4: 300 ops/h. The AC-4 ceiling at 300 ops/h is the hard limit for reversing duty — exceed that and the arcing time of 10–15 ms starts eating the contacts faster than the 10 million typical mechanical operations would suggest. For a conveyor line doing one reverse cycle every 12 seconds, that's within margin; for a press with continuous jogging, size up. At 500 V, the contactor is rated for 45 kW; at 690 V, 21.1 kW. The 500 V figure is the higher power point — that's the one to use if your motor nameplate sits at 480–500 V. The auxiliary contact ratings cover 24 V at 10 A, 60 V at 2 A, 110 V at 1 A, 220 V at 0.3 A, and 230 V at 6 A. Note the 230 V 6 A rating is for the coil circuit, not the main poles.