What it is and what it does
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. Rated surge voltage resistance is 6 kV, which puts it in the pollution degree 3 environment (industrial panels, not climate-controlled labs).
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. These are the make/break capacities for resistive or lightly inductive loads — the kind of duty you see in PLC output isolation, contactor coil switching, or indicator lamp circuits. 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. Contact reliability is specified as one incorrect switching operation per 100 million operations at 17 V, 1 mA — that's the dry-circuit performance. For a sourcing decision, this means the contacts handle low-energy signals (e.g., from a sensor or pushbutton) without needing gold plating. The mechanical life is 10 million operations typical.
Mounting and panel integration
Fastening is by screw and snap-on mounting onto a DIN rail. The 45 mm width and 57.5 mm height fit the standard S00 footprint. 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. The IP20 front protection means the terminals are finger-safe but the contactor is not sealed against dust or moisture — it belongs inside an enclosure.
Lifecycle and sourcing reality
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.