What it is and what it does
The Siemens 3RH2371-2FB40 is a SIRIUS auxiliary contactor, size S00, designed to switch control circuits and signal loads in motor control centers and industrial panels. It carries 7 instantaneous normally-open contacts, each rated at 10 A at 24 V, making it suitable for high-count signal multiplication or interlocking across multiple contactor coils and PLC inputs. The coil pulls in on 24 V DC with a 4 W holding power, and the built-in diode surge suppressor handles the inductive kickback — no external flyback diode needed across the coil terminals. Mechanical life is rated at 10 million operating cycles. The contactor can switch AC loads up to 10,000 operations per hour with an arcing time of 10 to 15 ms.
Mounting and integration
Mounts on a 35 mm DIN rail via the integrated snap-on latch, with screw terminals accepting 2 x 0.5 to 4 mm² solid or stranded wire. The S00 footprint takes up 45 mm width, 70 mm height, and 121 mm depth — plan the panel layout to leave 10 mm clearance above, below, and forward, plus 6 mm at the sides for airflow and wiring access. Mounting position is flexible: the contactor can be rotated ±180° on a vertical surface and tilted forward or backward by ±22.5°, which helps when fitting into tight or angled enclosures.
Ratings and what they mean for your circuit
The 10 A rating at 24 V DC is the continuous current each NO contact can carry in a control circuit. At higher voltages the current must be derated. The 7 NO contacts give you flexibility to wire multiple signal paths from a single coil — common in safety circuits where you need to mirror a status to several PLC inputs or to interlock multiple contactors. Operating temperature range is -25 to +60 °C, with storage from -55 to +80 °C. Pollution degree 3 means it's suited for industrial environments with conductive dust or occasional condensation — standard for most control panels.