The Siemens 3RH1344-1DG40-0KA0 is a SIRIUS auxiliary contactor, size S00, with four normally open (NO) instantaneous contacts and a 125 V DC coil that includes a built-in varistor for surge suppression. It's designed to switch control signals in a motor starter or contactor assembly — think of it as the logic-signal relay that tells the main power contactor when to close, or that feeds status back to a PLC. The coil draws 3.2 W during both closing and holding, so there's no inrush spike to size your DC supply around — steady-state power is the same as pull-in.
Contact ratings — the numbers that decide fit
Each NO contact is rated for switching at several common control voltages: 10 A at 24 V, 6 A at 230 V, 3 A at 400 V, 1 A at 690 V. At 125 V DC (the coil voltage), the contact rating isn't directly listed, but the 24 V and 110 V figures (10 A and 1 A respectively) bracket it; expect the 125 V DC contact rating to be closer to the 1 A mark. For a sourcing decision, this means the contacts handle low-energy signals (e.g., from a sensor or pushbutton) without needing gold plating.
Fastening is by screw and snap-on mounting onto a DIN rail. Depth is 111 mm. Wire terminations accept solid conductors: 2x (0.5 to 1.5 mm²), 2x (0.75 to 2.5 mm²), or 2x 4 mm².
Compliance documentation covers RoHS (substance prohibition date 07/01/2006) and the standard SIRIUS product declarations. The built-in varistor is the surge suppressor design, so no external RC snubber is needed for coil suppression on DC control circuits.