Siemens 3RU21261DB0 Thermal Overload Relay
Selection Trade-offs for SIRIUS 3RU2 Devices
The 3RU21261DB0 belongs to the Siemens SIRIUS 3RU2 thermal overload relay family (S0 frame, CL10), covering motor full-load currents in the 2.2–3.2 A band. When screening these relays against a given motor branch, engineers weigh three primary dimensions:
-
Trip-current band alignment — the relay's nominal range must bracket the motor's FLA with sufficient margin for thermal backup without nuisance tripping during normal acceleration. The 3RU21261DB0 covers 2.2–3.2 A; adjacent SIRIUS 3RU2 siblings extend from 1.8 A up to 25 A, allowing fine-step sizing across typical AC-3 motor ratings.
-
Coordination with the contactor — SIRIUS 3RU2 relays are listed for use with corresponding Siemens contactors (For Use With/Related Products field confirms "Contactors"). The overload relay mounts downstream of the contactor in a direct-on-line or reversing starter configuration; verify that the selected contactor's AC-3 current rating accommodates the combined branch load.
-
Accessory and signaling fit — base product number 3RU2126 spans multiple current classes; all share the same physical mounting (S0). If auxiliary contact blocks or front-mounting adapters are required, confirm that the selected variant's auxiliary contact slots accommodate the planned wiring scheme before ordering.
Key Specifications
| Parameter | Value |
|---|---|
| Accessory Type | Thermal Overload Relay |
| Series | SIRIUS 3RU2 |
| Base Product Number | 3RU2126 |
| Current Range | 2.2–3.2 A |
| For Use With | Contactors |
| Encapsulation | Bulk |
| RoHS Compliance | ROHS3 Compliant |
| Product Status | Active |
In-Catalog Comparison — 3RU21261DB0 vs. Similar SIRIUS 3RU2 Relays
All listed parts share the same series, accessory type, package, and base product number; they differ primarily in trip-current range. The reader must perform their own application qualification.
| Parameter | 3RU21261DB0 (seed) | 3RU21261CB0 | 3RU21261GB0 | 3RU21264DB0 |
|---|---|---|---|---|
| Current Range | 2.2–3.2 A | 1.8–2.5 A | 4.5–6.3 A | 20–25 A |
| Series | SIRIUS 3RU2 | SIRIUS 3RU2 | SIRIUS 3RU2 | SIRIUS 3RU2 |
| Stock (total) | 5 | 2 | 14 | 5 |
Why these are similar (catalog screening): All eight parts in the comparison share the same base product number prefix (3RU2126), the same thermal overload relay type, and identical mechanical/environmental package attributes (bulk, S0 frame, ROHS3, Active). The sole differentiation is the trip-current calibration, which steps continuously from 1.8 A to 25 A across the family.
Specific contrasts:
- 3RU21261CB0 (1.8–2.5 A) covers smaller motors; sits one step below the seed's band.
- 3RU21261GB0 (4.5–6.3 A) jumps two steps; suited for motors requiring roughly double the seed's upper current.
- 3RU21264DB0 (20–25 A) uses a different variant suffix (64 vs 61) and extends to the upper end of the S0 frame; typically paired with larger contactors in the same series.
The remaining four alternates (3RU21261EB0, 3RU21261FB0, 3RU21261JB0, 3RU21261HB0) fill intermediate bands between the seed and the upper range; stock counts and specific motor hp/amp ratings should be confirmed against the target load before selection.