Size S00 auxiliary contactor with varistor coil suppression
The Siemens 3RH2122-2UB40 is a SIRIUS auxiliary contactor in frame size S00, designed for switching control and signal circuits rather than main motor loads. Its 24 V DC coil includes a built-in varistor for surge suppression, which clips inductive voltage spikes at coil dropout — a detail that matters when the contactor shares a DC supply with sensitive PLC inputs or fieldbus slices.
Panel fit and mounting clearances
The 3RH2122-2UB40 measures 45 mm wide, 73 mm deep, and 70 mm tall — a compact footprint for a 2-pole auxiliary block. These clearances allow arc gases to vent and heat to dissipate; packing the contactor tighter than these figures derates the switching capacity, especially on DC loads where the arc lingers longer.
Switching duty and contact configuration
The contactor provides 2 NO instantaneous contacts. Mechanical endurance is 30 million typical cycles, which suits high-cycle applications like conveyor interlocking or valve sequencing where the auxiliary contactor sees every machine cycle. The DC coil closing power is 4 W — a modest draw that a 24 V DC power supply can handle without oversizing. The product extension auxiliary switch is available, meaning additional contact blocks can be stacked onto this base unit without removing wiring.