What it is and what it does
The Siemens 3RH1344-2DB40-0KA0-ZX95 is a SIRIUS auxiliary contactor in size S00, carrying 4 normally-open instantaneous contacts and a 24 VDC coil. It switches auxiliary circuits in motor starter and control panel applications — think signal interlocking, status feedback to a PLC, or extending the contact count on a main contactor. The coil draws 3.2 W closing and holding, so the DC supply needs to deliver that continuously; the built-in varistor suppresses the inductive kick on de-energisation.
Key ratings and what they mean for fit
Rated insulation voltage is 6 kV surge withstand, which puts it in the IEC 60947-1 overvoltage category III range — suitable for fixed-installation panels without additional surge protection upstream. The thermal current rating at 24 V is 10 A; at 230 V it derates to 6 A, at 400 V to 3 A, and at 690 V to 1 A. That derating curve tracks the arc-extinction limits in air at higher voltages — the 690 V figure is the one to check if you are switching control transformers on a 690 V line. Contact reliability is specified as one incorrect switching operation per 100 million at 17 V, 1 mA, which is the low-energy end — gold-flashed contacts would be better for PLC-level dry circuits, but this part is rated for the typical 24 VDC auxiliary load.
Mounting and integration
Fastens via screw or snap-on onto a DIN rail. The mounting position allows ±180° rotation on a vertical surface and ±22.5° tilt forward/backward, so it fits in tight enclosures where the rail is angled. Width is 45 mm, depth 114 mm, height 60 mm — the 114 mm depth is the dimension that matters when the panel door has a shallow clearance. Solid conductors from 0.25 to 2.5 mm² terminate in the screw terminals; strip length per standard practice, no ferrule required for solid wire. IP20 on the front means finger-safe but not washdown — keep it inside a closed cabinet.