Siemens 3RT1024-1KB40 — SIRIUS Power Contactor, Size S0, 24 VDC Coil
The Siemens 3RT1024-1KB40 is a SIRIUS power contactor in size S0, designed for switching motor loads up to 7.5 kW at 690 V. That matters when you're sizing a 24 V bus shared with PLCs and sensors; the contactor won't pull a transient that drops the rail below the logic threshold. The 45 mm width fits a standard 9 mm pitch panel layout — five units per 225 mm rail section. Side-by-side mounting is allowed with no derating, but if you're stacking them tight, the 6 mm side clearance to grounded metal still applies for the arc chamber.
In AC-2 duty (slip-ring motors, frequent start/stop) at 400 V, it delivers 5.5 kW. For AC-4 (plugging, inching, reversing) at 400 V, the current limit is 12.5 A. The AC-12 rating of 10 A covers resistive and solid-state loads at low switching frequency. The auxiliary contact block (not included) is rated for switching at 24 V: 10 A, at 60 V: 2 A, at 110 V: 1 A, at 220 V: 0.3 A. Those are the make/break capacities for the control circuit — if you're driving a PLC input at 24 V, the 10 A rating gives headroom, but at 220 V the 0.3 A limit means you can't directly switch a large contactor coil without a relay interface.
Type 1 coordination (welding allowed, no fire) uses a 63 A gL/gG fuse. The varistor surge suppressor is built in across the coil — no external snubber needed for inductive load switching.
IP20 on the front face protects against finger contact; the terminals are IP00, so the panel enclosure must provide the overall ingress rating. The screw terminals accept solid conductors 2x (0.5 to 1.5 mm²), 2x (0.75 to 2.5 mm²), or max 2x (0.75 to 4 mm²). Stranded: 2x (1 to 2.5 mm²), 2x (2.5 to 6 mm²), or max 2x 10 mm². AWG equivalents: 2x (16 to 12), 2x (14 to 10), 1x 8. Electrical life depends on the switching category and current; for AC-3 motor starts at rated power, expect roughly 1 to 2 million operations before contact wear.