What it is and what the ratings mean for fit
The Siemens 3RT1025-1AT60 is a SIRIUS power contactor in the S0 frame size, with three normally-open main contacts and screw-type terminals for the main current circuit. It's designed for switching motor loads in control panels, mounting via screw or snap-on onto a 35 mm DIN rail per DIN EN 50022. The 45 mm width and 91 mm depth are the dimensions that govern panel layout — the depth in particular matters when fitting into shallow enclosures or behind gland plates. The headline motor ratings: 7.5 kW at AC-2 duty class at 400 V, and 15.5 A at AC-4 at 400 V. AC-2 is the standard for slip-ring motor starting and reversing — the rating that governs the real-world load it can handle in those applications. AC-4 covers plugging and inching duty, where the contactor sees higher switching stress. For resistive or lightly inductive loads, the AC-12 maximum operating current is 10 A. The operating temperature range of -25 to +60 °C covers most industrial environments, and the IP20 front protection means it's safe for finger contact inside a closed panel.
Coordination and protection
For short-circuit protection, the contactor is coordinated with fuses. With type of coordination 2 (no damage to the contactor after a fault), the required fuse is gL/gG 25 A. With type 1 coordination (contactor may need replacement after a fault), the fuse can be up to 63 A gL/gG. This is the selectivity headroom a site electrical engineer needs to size the upstream protection without over-fusing and losing coordination.
Termination and wiring
Main circuit terminals accept solid conductors: 2x (0.5 to 1.5 mm²), 2x (0.75 to 2.5 mm²), and max 2x (0.75 to 4 mm²). For stranded conductors: 2x (1 to 2.5 mm²), 2x (2.5 to 6 mm²), and max 2x 10 mm². AWG equivalents are 2x (16 to 12), 2x (14 to 10), and 1x 8. The screw-type terminals are standard for panel builders — no special tooling needed, but torque to the manufacturer's spec during commissioning.