What the 24 VDC coil and 4 NO contacts mean for your control circuit
The 3RH2140-1SB40 is a SIRIUS coupling relay — a 4-pole normally-open auxiliary contactor designed to switch signal-level loads in control circuits, not motor power. The 24 VDC coil draws 1.6 W closing power, which is light enough that a standard PLC digital output or small control transformer can drive it without a separate interposing relay. At 24 V DC the contacts handle 10 A; at 220 V DC the rating falls to 1.2 A. This derating curve means the same relay can serve 24 V PLC I/O isolation and 230 V valve solenoids, but not a 480 V motor contactor coil without checking the inrush against the 3 A rating at 400 V. Built-in suppressor diode across the coil eliminates the need for an external flyback diode on DC circuits — one less component to place and wire. The pick-up threshold is 0.85× rated voltage (20.4 VDC) and the drop-out is 1.85× rated (44.4 VDC), giving a wide hysteresis that prevents chatter on a sagging 24 V bus.