What it is and what it does
The Siemens 3RT1024-1AL24-3MA0 is a SIRIUS power contactor in the S0 frame size, designed for switching motor loads in control panels. It carries a 24 VDC coil and is rated for AC-4 duty at 12.5 A at 400 V — that's the plugging/reversing/inching current, the toughest switching category for a contactor because it makes and breaks locked-rotor current. For AC-2 duty (slip-ring motors), it's rated at 5.5 kW at 400 V. The contactor mounts via screw or snap-on onto 35 mm DIN rail per EN 50022, and its 45 mm width means it occupies a single standard module slot. Side-by-side mounting is permitted, so you can gang multiple units without spacing gaps.
Key ratings and what they mean for your panel
The AC-4 rating of 12.5 A at 400 V is the one that governs for reversing or jogging duty — that's where the contactor makes and breaks the motor at standstill, drawing six to eight times rated current. If your application is simple on/off across-the-line starting (AC-3), the contactor will handle a higher current, but the evidence doesn't list that figure directly. The AC-2 rating of 5.5 kW at 400 V covers wound-rotor motors where the contactor switches the rotor circuit. Short-circuit coordination matters here. With Type 2 coordination (minimal damage to the contactor after a fault), the required upstream fuse is 25 A gL/gG. With Type 1 coordination (contactor may need replacement after a fault), it's 63 A gL/gG. That's the fuse the panel builder needs to spec — not the motor overload relay. The auxiliary contact block has 2 instantaneous contacts, rated at 10 A at 24 V, 6 A at 230 V, and 3 A at 400 V. That's enough for PLC inputs or relay coils in most control circuits. The coil draws 10 A at 24 V rated value — that's the inrush, not the hold; the hold current will be lower. Operating temperature range is -25 to +60 °C, which covers most indoor panel environments. Pollution degree 3 means it's rated for conductive pollution environments — typical for industrial control panels not in a clean room. Maximum operating altitude is 2 000 m without derating. Above that, you'd need to account for reduced air density affecting dielectric withstand and cooling.
Panel integration and wiring
Dimensions are 45 mm wide, 85 mm high, 140 mm deep. That's the S0 frame envelope — it fits the standard DIN rail footprint. The depth of 140 mm means you need at least that much clearance behind the panel door for the contactor body and wiring. Main circuit terminals accept screw-type connections: 2x (1 to 2.5 mm²) or 2x (2.5 to 6 mm²) stranded, max 2x 10 mm². For solid wire: 2x (0.5 to 1.5 mm²) or 2x (0.75 to 2.5 mm²), max 2x (0.75 to 4 mm²). AWG equivalents: 2x (16 to 12) or 2x (14 to 10), max 1x 8 AWG. That covers most motor leads up to about 4 kW at 400 V. Front face is IP20 — finger-safe when installed in an enclosure. The terminal area itself is IP00, so the contactor needs to be inside a panel with a door or cover. Mechanical endurance is rated at 10 million operations typical — that's the mechanical life before wear-out, not the electrical life under load. Electrical life will be shorter and depends on the switching current and duty cycle.
Sourcing and lifecycle
The 3RT1024-1AL24-3MA0 is the 24 VDC coil variant of the S0 frame contactor. If your BOM calls for a different coil voltage (e.g., 24 VAC, 110 V, 230 V), the frame size and ratings are similar but the coil suffix changes. The evidence doesn't list a direct successor or alternate MPN — this is the current production version.