What this S3 contactor is and where it fits
The Siemens 3RT7045-1AN20 is a size S3 contactor from the SIRIUS family, built for switching three-phase motor loads up to 690 V AC-3. It carries three normally-open main poles and screw-type terminals on both the main and auxiliary circuits. The front face is IP20 rated; the terminal area is IP00, meaning the wiring zone expects enclosure protection from the panel. Fastening is by screw or snap-on onto 35 mm or 75 mm standard mounting rail, with generous mounting-position tolerance — ±180° rotation on a vertical surface and ±22.5° tilt forward or backward.
AC-3 duty and switching cycle limits
The AC-3 maximum operating voltage is 690 V, which covers 400 V and 480 V line supplies with headroom. What matters for a motor-starting application is the switching frequency: the contactor is rated for 800 operations per hour under AC-3 (or AC-3e) duty, but that drops to 250 operations per hour under AC-4 — the heavier inching/plugging duty. If your application cycles a motor more than once every 14 seconds under AC-3, or once every 14 seconds under AC-4, this contactor will exceed its mechanical design rate. The holding power of the DC magnet coil is 0.27 W, with a closing surge of 0.62 W — low enough to keep the control transformer small.
Panel integration and wiring notes
The contactor occupies 70 mm width on the DIN rail, with a depth of 139 mm and height of 148 mm. Side-by-side mounting is permitted without derating, which simplifies multi-contactor motor starter assemblies. The screw terminals accept two conductors per clamp: solid or stranded from 0.5 to 1.5 mm², or 0.75 to 2.5 mm². Finely stranded wire with ferrule is handled the same way. The auxiliary switch block is field-addable — the product extension for auxiliary switches is supported. Pollution degree 3 rating means it's suited for industrial environments with conductive pollution, typical of control panels near production lines.