SIRIUS S0 power contactor — 24 V DC coil, screw terminals
The Siemens SIRIUS 3RT1024-3BD40-1AA0 is a power contactor in the S0 frame size, rated for switching motor loads and resistive circuits in industrial control panels. It mounts via screw or snap-on onto 35 mm DIN rail per DIN EN 50022, making it a direct fit for standard panel layouts. The 24 V DC coil draws 5.4 W during both closing and holding, so the control transformer and power supply need to budget for that steady-state draw — no inrush spike to size for, but the continuous 5.4 W per contactor adds up across a multi-contactor panel.
Key ratings and what they mean for fit
The DC switching ratings are the ones that govern fit for this contactor: 10 A at 24 V DC, 2 A at 60 V DC, 1 A at 110 V DC, 0.3 A at 220 V DC, and 6 A at 230 V DC. These are not continuous thermal currents — they are the make/break capacities for DC loads, where arc extinction is harder than AC. For AC motor duty, the contactor is rated 5.5 kW at AC-2, 400 V, and 12.5 A at AC-4, 400 V. AC-2 covers slip-ring motor starting; AC-4 covers plugging and inching. The AC-12 rating of 10 A operating current applies for resistive loads. The operating temperature range is -25 to +60 °C, which covers most indoor panel environments but needs derating consideration if mounted in a non-ventilated enclosure near other heat sources.
Termination and wiring
Main circuit connections use screw-type terminals. The terminal accepts solid or stranded conductors: 2x (0.25 to 2.5 mm²), 2x (1 to 2.5 mm²), 2x (2.5 to 6 mm²), or up to 2x 10 mm². AWG equivalents are 2x (16 to 12), 2x (14 to 10), or 1x 8. The 45 mm width and 85 mm height fit the S0 footprint; depth is 101 mm, which matters for enclosure depth clearance when the contactor is mounted with auxiliary blocks or a surge suppressor on the front. IP20 on the front, IP00 at the terminals — the terminals are live when wired, so the panel door or a terminal cover provides the touch protection.
Coordination and fusing
For type 1 coordination (no damage to the contactor but may need contact replacement after a fault), the required upstream fuse is gL/gG 63 A. For type 2 coordination (contactor remains operational after a fault), the fuse is gL/gG 25 A. These are per IEC 60947-4-1 and define the short-circuit protection the contactor needs to meet its rated SCCR. The degree of pollution is 3 (conductive pollution or dry non-conductive pollution that becomes conductive due to condensation), which is typical for industrial control panels not in a sealed clean environment.