What it is and where it fits
The Siemens SIRIUS 3RT1025-3KC80 is a size S0 power contactor with a 24 VDC magnet coil, built for switching motor loads in control panels. It mounts via screw or snap-on onto 35 mm DIN rail per EN 50022, so it drops into standard panel layouts without adapters.
Motor-duty ratings that decide the fit
In AC-3 duty (squirrel-cage motor starting) at 400 V, this contactor is rated for 7.5 kW; at 500 V it handles 10 kW, and at 690 V it reaches 11 kW. The AC-4 rating at 400 V is 15.5 A — that's the inching/plugging current limit, not the continuous motor current. For a 400 V line, the 7.5 kW AC-3 figure is the one that governs the motor FLA you can switch.
Coil and control circuit
The 24 VDC coil draws 4.2 W for both closing and holding — no power drop after pull-in, so the control transformer or DC supply must sustain that continuously. Switching capacity on the coil side: 10 A at 24 V, 2 A at 60 V, 1 A at 110 V, 0.3 A at 220 V, 6 A at 230 V, 3 A at 400 V. The built-in varistor suppressor clips the inductive kick, which saves adding an external diode or RC snubber on the panel layout.
Coordination and fusing
For Type 1 coordination (no weld prevention, just clearing the fault) the required upstream fuse is gL/gG 63 A. For Type 2 coordination (limited contact damage, minimal downtime) it's gL/gG 25 A. That's the fuse the panel builder needs to spec — not the contactor's own rating.
Environmental and mounting limits
Operating temperature range is -25 to +60 °C, with a maximum operating altitude of 2 000 m. The contactor body carries IP20 on the front (finger-safe), while the terminals themselves are IP00 — so the panel enclosure provides the touch protection. Pollution degree 3 means it's rated for conductive pollution environments typical of industrial control panels. Side-by-side mounting is permitted with 6 mm spacing at the side.
Termination details
Main circuit terminals are screw-type, accepting 2x (0.25 to 2.5 mm²) solid or 2x (1 to 2.5 mm²) stranded, with a maximum of 2x 10 mm². AWG equivalents: 2x (16 to 12) solid, 2x (14 to 10) stranded, or 1x 8. That covers standard panel wire sizes up to about 8 AWG for the power circuit.