What it is and where it fits
The Siemens 3RT1025-1AF00-1AA0 is a SIRIUS S0-size power contactor with three normally-open main contacts, designed for switching motor loads and resistive loads in industrial control panels. It mounts on a 35 mm DIN rail per DIN EN 50022, using either a screw-fixed or snap-on method — so it drops straight into a standard panel layout without adapters. The coil is rated 24 VDC, and the contactor draws 10 A at that voltage (AC-12 duty). For motor switching, the AC-2 rating at 400 V is 7.5 kW, and the AC-4 rating at 400 V is 15.5 A — so it handles reversing or inching duty cycles where the contacts make and break under load. The front face is IP20 (finger-safe), while the terminals are IP00 — meaning the wiring area is open and needs to be inside an enclosure or guarded. Keep that in mind during panel layout: the terminal zone isn't touch-safe on its own.
Key ratings and what they mean for your BOM
The contactor is rated for switching at 50 Hz, with a rated control supply voltage of 110 V at 50 Hz. The main circuit handles up to 11 kW at 690 V and 10 kW at 500 V — so it's sized for moderate three-phase motor loads in 400 V or 690 V systems. For DC switching, the ratings drop with voltage: 10 A at 24 V, 2 A at 60 V, 1 A at 110 V, 0.3 A at 220 V, and 6 A at 230 V. That's typical for a contactor — the arc extinguishes less efficiently on DC, so the current capacity falls as voltage rises. If you're switching DC loads, size accordingly. The contactor is rated for 10 million mechanical operations (typical), which is solid for a size S0 frame. It operates from -25 °C to +60 °C and is rated for pollution degree 3 — so it's fine in typical industrial environments with conductive dust or humidity, but not for submersion or washdown zones.
Wiring and integration details
Main circuit terminals are screw-type, accepting solid or stranded conductors: 2x (0.5…1.5 mm²), 2x (0.75…2.5 mm²), and up to 2x (0.75…4 mm²) for the smaller range; for larger wires, 2x (1…2.5 mm²), 2x (2.5…6 mm²), and max 2x 10 mm². AWG equivalents are 2x (16…12), 2x (14…10), and 1x 8. That covers most panel wiring up to about 8 AWG. The contactor is 45 mm wide, 85 mm tall, and 91 mm deep — a compact S0 footprint that fits alongside other SIRIUS components on the rail. Side-by-side mounting is allowed, with a 6 mm gap to the side for airflow and arc clearance. No forced spacing needed, but don't crowd it tight. For short-circuit protection, type 1 coordination calls for a 63 A gL/gG fuse; type 2 coordination requires a 25 A gL/gG fuse. That's the difference between a fuse that blows and protects the contactor (type 2) versus one that allows limited damage to the contactor (type 1). Match the fuse to your coordination requirement.