The Siemens SIRIUS 3RT2015-1SB42 is a Size S00 coupling contactor — a 24 VDC coil, screw-type terminal block with a 45 mm wide footprint that wires up clean on a 35 mm DIN rail. This is the part you reach for when you need to switch a DC load in a control panel and the coil voltage is fixed at 24 VDC. The contactor is rated for 10 A at 24 VDC, 2 A at 48 VDC, and 0.75 hp at 230 V, so it handles small motors, solenoid valves, and signal-level loads within a compact envelope.
The screw terminals accept solid or stranded wire from 0.5 to 4 mm², and can take two conductors per clamp (2x 0.5-1.5 mm², 2x 0.75-2.5 mm², or 2x 4 mm²). That means you can daisy-chain a feed-through without an extra terminal block, which keeps the wiring channel clean. The contactor has no built-in auxiliary switch, so if you need a feedback signal to a PLC input, you add a separate auxiliary contact block.
Switching performance and thermal limits
The maximum switching frequency depends on the duty class: 1,000 cycles per hour for AC-1 resistive loads, 750 cycles per hour for AC-2 and AC-3 motor starts, and 250 cycles per hour for AC-4 plugging or inching duty. The coil pick-up voltage is 0.85 x rated (20.4 VDC) and drop-out is 1.85 x rated (44.4 VDC), so it holds in during a brownout but drops cleanly when the control voltage disappears.