What it is and what it does
The Siemens 3RT1025-1AG64 is a SIRIUS power contactor in the S0 frame size, designed for switching motor loads in industrial control panels. It's rated for 7.5 kW at 400 V in AC-2 duty (slip-ring motor starting) and 15.5 A at 400 V in AC-4 duty (plugging/inching), so it handles the high inrush and frequent switching of reversing or jogging applications. The coil is wound for 100 V at 50 Hz or 100–110 V at 60 Hz, with an operating range of 0.8–1.1 times rated voltage at 50 Hz and 0.85–1.1 at 60 Hz — meaning it holds in through brownouts down to about 80 V at 50 Hz.
Mounting and integration
Mounts via screw or snap-on onto 35 mm DIN rail per DIN EN 50022. The 45 mm width and 85 mm height fit a standard panel slot; depth is 140 mm. Side-by-side mounting is permitted with no derating gap.
Termination and wiring
Main and auxiliary circuits use screw-type terminals. Main contacts accept solid 2x (0.5–1.5 mm²), 2x (0.75–2.5 mm²), max 2x (0.75–4 mm²), or stranded 2x (1–2.5 mm²), 2x (2.5–6 mm²), max 2x 10 mm². AWG equivalents: 2x (16–12), 2x (14–10), 1x 8 for main; 2x (20–16), 2x (18–14), 1x 12 for auxiliary. The IP20 front protection keeps fingers out; the terminal area is IP00, so live parts are exposed — standard for panel-mount contactors, but watch clearance if the panel door opens live.
Protection and coordination
For Type 2 coordination (no damage to the contactor under short circuit), use a gL/gG fuse rated 25 A. For Type 1 coordination (contactor may need replacement after fault), the fuse can be 63 A. This lets you balance protection level against fuse size depending on the upstream breaker and downstream motor thermal protection.