What the ratings mean for fit
The 3RT7045-1AL20 carries three NO main contacts and zero NC main contacts — a straightforward 3-pole make configuration for switching three-phase loads. The AC-3 maximum operating voltage of 690 V means it can switch motor loads on a 400 V or 690 V line, but the current capability drops with voltage: at 230 V it is rated 6 A, at 400 V it is rated 3 A, and at 690 V it is rated 1 A. For DC switching, the DC-13 rating at 220 V is 0.3 A. The maximum switching frequency is 800 operations per hour in AC-3 and 250 per hour in AC-4 (plugging/inching duty). The auxiliary contacts are rated for PLC-level signals — the contact reliability is specified as acceptable for PLC control at 17 V, 5 mA, so the aux contacts will reliably switch a 24 VDC PLC input without needing a separate interface relay.
Mounting and integration
Mounting is via screw or snap-on onto 35 mm or 75 mm standard mounting rail. The mounting position is flexible: +/-180° rotation on a vertical surface, and can be tilted forward/backward by +/-22.5° on a vertical surface. Side-by-side mounting is permitted with no derating gap required. The contactor is size S3, with dimensions of 70 mm width, 148 mm height, and 139 mm depth — check that the enclosure depth clears the 139 mm plus wiring bend radius. Wire sizes accepted: 2x (0.5 to 1.5 mm²) solid or stranded, and 2x (0.75 to 2.5 mm²) finely stranded with ferrule. Pollution degree 3 (conductive pollution, typical for industrial control panels) is the rated environment. The surge voltage resistance is 6 kV, and the rated insulation voltage is 690 V.