What it is and what it does
The Siemens SIRIUS 3RT1025-3BB40-ZX95 is a size S0 power contactor with a 24 VDC coil, 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 screw or snap-on mounting. Rated for 10 A at 24 V (AC-12) and 10 kW at 500 V, it covers a broad range of motor and general switching duties. The AC-4 rating at 400 V is 15.5 A, which is the figure to watch for reversing or inching applications where the contactor makes and breaks motor current under load.
Key ratings and what they mean for fit
The 24 VDC coil draws 5.4 W for both closing and holding, so the control transformer or power supply must be sized for that inrush. The holding power is the same as closing — no drop-off — meaning the coil stays at full dissipation continuously. Pollution degree 3 (industrial environment, conductive pollution) and IP20 on the front face mean the contactor is suited for enclosed panels where the front is protected from accidental contact. The terminal area is IP00 — bare terminals — so finger-safe shrouds or a dead-front cover are needed if the panel is live. Operating temperature range is -25 to +60 °C, with a maximum operating altitude of 2 000 m. Side-by-side mounting is allowed with a 6 mm clearance to adjacent devices, which helps pack multiple contactors in a row on the DIN rail. Mechanical endurance is 10 million cycles typical, so this contactor is built for high-cycle applications like conveyor or packaging lines where the contactor switches frequently.
Wiring and coordination
Main circuit terminals are screw-type, accepting 2x (0.25 to 2.5 mm²) solid or 2x (1 to 2.5 mm²) stranded, up to 2x 10 mm² or 1x 8 AWG. For type 2 coordination (no damage to the contactor on a short circuit), use a 25 A gL/gG fuse upstream; for type 1 (contactor may need replacement after a fault), a 63 A gL/gG fuse is allowed.