What it is and what it does
The Siemens 3RH1344-1BG40 is a SIRIUS auxiliary contactor — a relay block that extends the control-circuit switching capacity of a main contactor or provides standalone signal switching in a panel. It carries 4 normally-open instantaneous contacts, meaning it closes the circuit the moment the coil is energized, with no built-in delay. That makes it a straight swap-in for any 4 NO auxiliary requirement in a motor control center or PLC output interface. Rated for 10 A at 24 V (AC-12 duty), it handles typical control loads like contactor coils, indicator lamps, and solenoid valves without derating at that voltage. At 230 V the rating drops to 6 A, and at 400 V it's 3 A — the thermal curve follows the standard IEC 60947-5-1 derating for auxiliary contacts. The 6 kV rated surge voltage resistance means it can sit on the same panel as drives and switching supplies without flashover on transient events.
Panel fit and mounting
The 3RH1344-1BG40 snaps onto a 35 mm DIN rail (EN 60715) or screws directly to a mounting plate. At 45 mm wide and 57.5 mm tall, it occupies a single modular slot — the same footprint as the S00 contactor frame it's designed to companion. Depth is 111 mm, which includes the coil terminals and contact screws; plan for that plus finger space when laying out the gland plate. Mounting position is flexible: the contactor can be rotated ±180° on a vertical surface and tilted forward or backward by ±22.5°. That's useful when the panel layout forces a non-standard orientation — the contactor's mechanical life of 10 million operations (typical) holds across those positions. Wire terminals accept solid conductors from 0.5 mm² up to 4 mm², with dual entry for daisy-chaining on the smaller sizes. The IP20 front protection means it's safe for finger-probe access inside a closed panel; no special cover needed for the terminals.
Environmental and compliance
Operating temperature range is -25 to +60 °C, with storage and transport tolerance from -55 to +80 °C. That covers most indoor industrial environments and unheated warehouses. Shock resistance is tested at 10 g for 5 ms and 5 g for 10 ms — enough for machine-mounted applications near presses or conveyors. The part is RoHS compliant per the 2006/07/01 substance prohibition date, and the degree of pollution is rated 3 (conductive pollution or dry non-conductive pollution that becomes conductive due to condensation). That's the standard industrial pollution severity for an enclosed panel — no special conformal coating needed for the contactor itself.
Coil and switching details
The DC magnet coil draws 3.2 W both at pickup and hold — no power drop after closure, which is typical for DC-operated contactors. That 3.2 W load needs to be factored into the PLC output or relay driving it; a 24 VDC output card with a 0.5 A per channel rating can drive several of these in parallel, but check the total current budget. 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 low-energy signals. For gold-flashed or bifurcated contacts you'd see better, but for a standard silver-alloy contact this is a solid figure for PLC input sensing or low-current interlock circuits.