ABB TA25DU-5.0M Thermal Overload Relay

Order No.: 1SAZ211201R2035

TA25DU-5.0M is a 3-phase bimetallic thermal overload relay in the TA25DU series. The M variant is designed for AX series contactors (non‑M versions fit A series contactors). It provides motor overload and phase failure protection.

✅ Core Technical Parameters

Adjustable current range: 3.5 ~ 5.0 A

Trip Class: 10A (standard motor protection)

Rated main circuit voltage: AC 690V / DC 440V

Poles: 3-pole protection

Auxiliary contacts: 1NO + 1NC (one changeover contact)

Reset mode: Manual / Automatic reset selectable

Built-in functions: Temperature compensation, phase failure protection, test button, STOP function, trip indication, trip-free mechanism

Compatible contactors: AX09, AX12, AX18, AX25 (direct plug-in mounting)

Standalone mounting: Requires separate mounting base as an accessory

📌 Type Code Definition

TA: Thermal Overload Relay

25: Frame rated current 25A

DU: Universal bimetallic type

5.0: Maximum setting current 5A

M: Version for AX contactors (differentiated from older TA25DU-5.0 for A contactors)

📋 Typical Applications

Protection for 0.75~2.2kW 3-phase asynchronous motors (380V), applied on machine tools, fans, water pumps, conveyors and compressors. It forms a motor starter circuit together with ABB AX contactors.

⚠️ Selection & Replacement Guidelines

1. Same-series replacement: TA25DU-5.0 (older version for A contactors; pin layout differs and cannot be directly interchanged)
2. Domestic alternatives: Delixi, Chint thermal relays with 3.5–5A range (verify contact configuration, trip class and mounting base)
3. Coordination: Short-circuit protection shall be implemented with fuses or circuit breakers. This relay only provides overload & phase failure protection, not short-circuit protection.

📎 Auxiliary Contact Ratings (AC-15)

400V: NC 0.75A, NO 0.37A

240V: NC 3A, NO 1.2A

120V: NC 3A, NO 1.5A

Operating Principle of ABB TA25DU Bimetallic Thermal Overload Relays

Core principle: Thermal effect of electric current + differential bending of bimetallic strips; inverse-time overload & phase failure protection. It only works with contactors for motor overload protection and cannot protect against short circuits.

1. Basic 3-phase Structure

Each phase is equipped with: heating element + bimetallic strip. Additional components: differential slide plate, temperature compensation strip, quick-trip mechanism, 1NO+1NC auxiliary contacts (95/96 NC, 97/98 NO), setting knob, reset mechanism and test button.

Bimetallic strip: Two metals with different thermal expansion coefficients bonded together; it bends toward the lower-expansion side when heated.

2. Normal Operation

Three-phase current equals the set value. Heat generation is low, and the bimetallic strip only bends slightly, not enough to trigger the trip mechanism. The 95-96 NC contact remains closed, the contactor coil stays energized, and the motor runs normally.

3. Overload Protection (Inverse-time Characteristic)

Sustained motor overload → current exceeds setting → heating element keeps rising in temperature, and the bimetallic strip bends further with accumulated heat.

Once the deformation threshold is reached, the quick-trip mechanism releases, the 95-96 NC contact opens, the ABB contactor coil de-energizes, main contacts break and the motor stops.

Feature: Inverse-time characteristic: Higher overload current leads to faster tripping. Short starting inrush current will not cause false tripping (Trip Class 10A, standard rating for TA25DU series), simulating the thermal inertia of motor windings.

4. Phase Failure (Phase Loss) Protection (Built-in Differential Mechanism on TA25DU)

When three-phase current is unbalanced or one phase is lost:

The open phase carries nearly zero current; its bimetallic strip cools down and springs back.

The other two phases draw much higher current, and their bimetallic strips keep bending.

The differential slide plate amplifies the deformation difference, triggering tripping much faster than regular balanced overload protection. This prevents motor burnout due to phase loss, a standard feature on ABB DU-series thermal relays.

1) Direct Cross-Brand Equivalent (TA25DU-5.0M, 3.5~5A)

2) Full Series Cross Reference Table (TA25DU-M vs Competitors)

Part 3: Extended Frame Sizes (TAxxDU-M Series)

TA42DU-M: For AX40~AX50 contactors, 25～42A

TA75DU-M: For AX65~AX80 contactors, 25～75A

TA80DU / TA110DU / TA200DU: High-current models (90～200A)

Part 4: Field Replacement Notes

1. Non-interchangeable base: TA25DU-M only plugs onto AX contactors; older TA25DU fits A contactors. Mismatched mounting will cause loose connection and overheating.
2. Strictly match current range: Select relays with fully overlapping setting ranges; never use higher current ratings to replace lower ones.
3. Phase failure protection: TA25DU has built-in differential phase-loss protection. Siemens 3RU and Schneider LRD also include this function; confirm this feature before purchasing low-cost domestic models.
4. Reset mode: Keep manual/automatic reset consistent with the original unit to avoid unintended auto-restart for unattended equipment.

Part 5: Simplest Replacement Plan for TA25DU-5.0M

Import alternatives: Schneider LRD07C, Siemens 3RU6116-1FB0

Domestic alternatives: Chint NR2-25/Z 5, Delixi CDR6-25 5

OEM same-model replacement: TA25DU-5.0M (Order No. 1SAZ211201R2035)