For motors with a full-load current between 1.8 … 2.5 A, the Siemens 3RU2126-1CB0 is the size S0 SIRIUS 3RU2 bimetal overload relay, trip CLASS 10, designed to plug straight onto a 3RT2 contactor. It has 1 NO + 1 NC auxiliary contacts: the NC contact opens the contactor coil circuit on overload and the NO contact can signal the trip to the PLC.
At 1.8 … 2.5 A this relay suits motors of roughly 0.75 kW at 400 V (per the Siemens AC-3 rating), but the setting must always follow the nameplate current, not the kW value.
See our Siemens industrial controls for matching 3RT2 contactors in size S0.
Technical data
| Siemens order number | 3RU2126-1CB0 |
|---|---|
| Product | SIRIUS 3RU2 thermal overload relay |
| Size | S0 |
| Current setting range | 1.8 … 2.5 A |
| Trip class | CLASS 10 |
| Auxiliary contacts | 1 NO + 1 NC |
| Rated operating voltage | 690 V |
| Motor power at 400 V (approx.) | 0.75 kW |
| Mounting | Contactor mounting (size S0) |
| FLA, 3-phase motor at 480 V (UL) | 2.5 A |
| Power loss (hot, total) | 5.7 W |
| Ambient temperature (operation) | -40 … +70 °C |
| Dimensions (W x H x D) | 45 x 85 x 85 mm |
| Net weight | 0.156 kg |
| Condition | New, original Siemens |
Typical applications
- Star-delta starters (set to 0.58 x motor current in the phase leg)
- Protection of motors with rated current 1.8 … 2.5 A
- Pumps, fans and conveyors in water, HVAC and packaging plants
- Replacement of an aged or damaged overload relay
Compatibility and replacement
Plugs directly onto 3RT2 contactors of size S0 (3RT202x). For separate (stand-alone) mounting Siemens offers a terminal support. For electronic protection with a wider setting range Siemens offers the 3RB3 series.
Frequently asked questions
Which contactor does it fit?
SIRIUS 3RT2 contactors of size S0.
What motor size does it suit?
Per Siemens the range corresponds to about 0.75 kW at 400 V (AC-3), but always set it by the motor rated current, not by the kW rating.
How do I set it?
Turn the setting dial to the motor rated current from the nameplate, within 1.8 … 2.5 A.
How fast can you deliver, and is there a warranty?
Air shipping usually takes 5 to 7 days once the part is ready, to almost any country. Each part is new and original with a 1-year warranty. Message us on WhatsApp with the order number for a quotation.
Before you order
Compare the complete order number on the old unit with this page, including the suffix: in most ranges the last characters set the coil voltage, current range or version. If the label is worn, send us a photo and we will identify the part.
Every part RendatSP supplies is new and original, carries a 1-year warranty and ships worldwide by air in 5 to 7 days once ready (shipping, payment and warranty). Send us the order number and quantity on WhatsApp or through the inquiry form and we will quote the same working day. Agents in Saudi Arabia, Iraq, the UAE, Egypt, Oman, Libya, Morocco, Mauritania, Yemen, Algeria and Jordan.
