Siemens 3RT2025-1AC20 Motor Contactor

Product Series: SIRIUS 3RT2 3-pole Power Contactor (Motor Contactor)

Full Order No.: 3RT2025-1AC20

✅ Model Code Explanation

3RT: SIRIUS contactor series

2: New generation SIRIUS Innovations

0: 3-pole motor contactor

25: S0 frame size, AC-3 17A, rated for 7.5kW motor at 400V

1: Built-in 1NO + 1NC auxiliary contacts

A: AC coil

C: 24V AC, 50/60Hz coil

20: Screw-type terminal

✅ Core Technical Specifications

✅ Typical Applications

Start/stop control of 3-phase asynchronous motors (fans, pumps, conveyors)

HVAC, packaging, machine tool automation control cabinets

Can be matched with 3RU2 thermal relays for motor overload protection; auxiliary contacts, surge suppressors and mechanical interlock modules can be added.

✅ Coil Variant Reference for Selection & Replacement

3RT2025-1AC20: 24V AC

3RT2025-1AG20: 110V AC

3RT2025-1AN20: 220V AC

3RT2025-1AP00: 230V AC

3RT2025-1BB40: 24V DC

✅ Replacement Information

1. Siemens internal replacement: Old model 3RT1025-1AC20 (discontinued). Direct replacement with 3RT2025-1AC20, mounting dimensions are compatible.
2. Domestic alternative reference: Chint NC1-18, Delixi CJX2-1810 (match coil voltage and confirm 1NO+1NC auxiliary contacts).

✅ Troubleshooting Guidelines

1. Coil energized but no pull-in: Measure A1/A2 for 24V AC; check burnt coil and loose terminals.
2. No output on main circuit after pull-in: Main contacts erosion, inspect L1/L2/L3 and T1/T2/T3.
3. Repeated coil burnout: Overvoltage or surge on coil circuit. RC snubber module is recommended for parallel connection.
4. Abnormal auxiliary contacts: Auxiliary contacts worn out. External auxiliary contact modules can be fitted.

The built-in 1NO+1NC auxiliary contacts integrated inside 3RT2025-1AC20 cannot be replaced separately.

They are integrated into the contactor housing with no spare parts available. Once the built-in auxiliary contacts are damaged, the whole contactor must be replaced.

Distinguish two concepts:

1. Built-in auxiliary contacts (1NO+1NC): Integrated inside S0 frame body, non-detachable and non-replaceable individually.
2. External add-on auxiliary contact modules (front-mounted / side-mounted): Detachable and replaceable separately, classified as accessories.

📌 External Auxiliary Contact Module Selection (Detachable & Replaceable)

1) Front-mounted (fit only 1 piece on front face)

3RH2911-1HA11: 1NO+1NC

3RH2911-1HA22: 2NO+2NC

2) Side-mounted (can be fitted on left or right side, max 2 pieces, one on each side)

3RH2921-1DA11: 1NO+1NC

3RH2921-1DA20: 2NO

3RH2921-1DA02: 2NC

🛠️ Fault Handling Solutions

1. Burnt built-in auxiliary contacts: No spare parts available; replace the entire 3RT2025-1AC20 contactor.
2. Damaged external auxiliary contact module: Remove the faulty auxiliary contact module and replace it with the same model accessory; reuse the contactor body.
3. Insufficient contact quantity: Add front/side mounted auxiliary contact modules listed above.

⚠️ Additional Remarks

For S0 frame (3RT2025), no separate spare main contact kits are available. The whole contactor needs replacement when main contacts are burned. Only S2 and larger frame contactors have independent spare main contacts.

Siemens 3RT2025-1AC20 Main Contacts vs Auxiliary Contacts

1. Definition & Function

Main Contacts (L1/L2/L3 ↔ T1/T2/T3)

Function: Switch high-power main circuit, directly turn on/off motors and loads

Quantity: 3 normally-open sets (3P)

Rating: AC-3 17A@400V for 7.5kW motor; AC-1 40A for resistive load

Circuit: High-power main circuit

Structure: Oversized thick silver-alloy contacts with arc extinguishing chamber to withstand breaking arc under high current

Remark: S0 frame, main contacts cannot be replaced individually. Full contactor replacement required after damage.

Auxiliary Contacts (Built-in 1NO+1NC, expandable with 3RH accessories)

Function: Signal feedback, interlock, latching (control circuit logic, not for high-power load driving)

Quantity: Built-in 1NO +1NC. Expandable by external modules

Rating: Low current, typically ≤6A for PLC input, relay coils and indicator lamps

Circuit: Low-power control circuit

Structure: Small silver contacts without heavy-duty arc extinguishing, only for small current breaking

Remark: Built-in auxiliary contacts are integrated and non-replaceable; external 3RH auxiliary modules can be assembled and replaced individually.

2. Comparison Table

3. Typical Wiring Example
4. Main Contacts: 3-phase power supply feeds L1/L2/L3 on contactor top terminals; bottom terminals T1/T2/T3 connect to motor.
5. Auxiliary Contacts

13-14 (NO normally open): Latching circuit or send “contactor energized” feedback signal to PLC.

21-22 (NC normally closed): Electrical interlock (forward/reverse circuit, prevent simultaneous pull-in of two contactors causing 3-phase short circuit).

4. Fault Differentiation

Main Contacts Failure: Motor weak rotation, phase loss, overheating or arcing at terminals, load cannot power up normally.

Auxiliary Contacts Failure: Motor can start/stop normally, but latching fails, loss of feedback signal, interlock invalid. Main power circuit remains unaffected.

5. Important Warning

Never use auxiliary contacts to switch motors, heaters or other high-power loads. Contact erosion will occur rapidly. High-power loads must be wired via main contacts.

Siemens 3RT2025-1AC20｜Application Scenarios of Main Contacts and Auxiliary Contacts

1. Main Contacts (L1/L2/L3 ↔ T1/T2/T3, 3 sets of high-power normally-open contacts)

Core purpose: Switch high-power main circuit and carry load operating current

✅ Applicable scenarios:

1. Direct start-stop of 3-phase motors (most common): Pumps, fans, conveyors, air compressors, machine tool spindle motors. This model is rated for 7.5kW 400V 3-phase motors.
2. 3-phase resistive load control: 3-phase heating elements, large 3-phase dehumidification heaters, max 40A under AC-1 rating.
3. High-power switching in power distribution circuits: Power switching for heavy loads inside control cabinets.

❌ Not suitable for:

PLC signals, indicator lamps, small relay coils and other low-current control circuits;

Logical interlock or status feedback.

Features: Equipped with arc extinguishing chamber and thick silver contacts, withstand motor inrush current and breaking arc.

1. Auxiliary Contacts (Built-in 1NO+1NC, terminals:13-14 NO,21-22 NC; expandable with 3RH external modules)

Core purpose: Low-current signal in control circuit, only transmit logic status, no high-power load driving

✅ Normally Open NO (13-14) Typical Scenarios

1. Contactor latching (self-holding): Maintain coil energized after releasing start pushbutton to keep motor running continuously.
2. Running status feedback: Send signal to PLC, DIO module or indicator lamp for HMI to display “contactor pulled in, equipment running”.
3. Sequential startup: Use NO contact to trigger coil of next relay/contactor after this contactor pulls in, to realize sequential start-up.

✅ Normally Closed NC (21-22) Typical Scenarios

1. Electrical interlock (classic application): Connected in series to coil circuit of reverse contactor in forward/reverse control circuit, to avoid 3-phase short circuit caused by simultaneous pull-in of forward and reverse contactors.
2. Fault / stop feedback: NC closed when contactor is open, used for stop status acquisition.
3. Safety circuit interlock: NC contact conducts when contactor is de-energized, serving as ready signal.

Auxiliary contacts are low rated (AC-15 approx.6A), only for low-current control circuits. Do NOT use auxiliary contacts to directly control motors or high-power heating loads.

Quick Selection Rule

Motors, high-power heaters, 3-phase power → Main Contacts

Latching, interlock, PLC signal, running indicator lamp, logic linkage → Auxiliary Contacts

On-site Quick Fault Diagnosis

Motor fails to run, phase loss, hot or arcing terminals → Most likely main contact fault

Motor can start and stop, but stops immediately once start button released, no running feedback, risk of short circuit due to failed interlock → Most likely auxiliary contact fault