Siemens 3WT2M40 ETU35WT F-4P Air Circuit Breaker (ACB)

1.In-depth Model Breakdown (3WT2M40 ETU35WT F-4P)

2. Core Technical Parameter Table

2.1 Basic Electrical Parameters

2.2 ETU35WT Trip Unit Protection Parameters

2.3 Mechanical and Environmental Parameters

3. Working Principle and Protection Mechanism

3.1 Core Working Principle

1. Fonctionnement normal: When the circuit breaker is closed, the main contacts connect the circuit, current flows through the main circuit and the trip unit sampling circuit, and the ETU35WT monitors the three-phase current in real time.
2. Fault Detection: When the current exceeds the set value, the ETU35WT calculates the trip time according to the protection characteristic curve.
3. Trip Action: When the trip condition is met, the ETU35WT sends a trip signal to drive the electromagnetic tripping mechanism to operate and quickly open the main contacts.
4. Arc Extinguishing Process: The arc generated when the main contacts are opened is quickly extinguished by the arc extinguishing chamber, preventing arc reignition and phase-to-phase short circuit.

3.2 Detailed Explanation of Three-stage Protection Functions (ETU35WT LSI)

3.2.1 Overload Long-time Delay Protection (LT/L)

Principle: Based on the inverse time-lag characteristic (heat accumulation principle), the higher the current, the shorter the trip time (following the I²t law)

Application: Protect cables and motors from long-term overload damage, and withstand short-term overcurrent during motor startup

Setting: Ir = 0.4~1.0×In, usually set to the rated current of the protected equipment

3.2.2 Short-circuit Short-time Delay Protection (ST/S)

Principle: Definite time-lag characteristic, set a fixed trip time (0.1s~0.5s) to achieve selective protection

Application: Remain closed before the lower-level circuit breaker operates, only cut off the fault branch, and improve power supply continuity

Setting: Isd = 1.5~10×Ir, usually set to 5~8×Ir, with the time coordinated with the lower-level circuit breaker

3.2.3 Instantaneous Short-circuit Protection (INST/I)

Principle: No time-lag characteristic, trip immediately when the current exceeds the set value (≤ 0.02s)

Application: Protect the circuit breaker itself and upper-level equipment from damage caused by huge short-circuit current (usually ≥ 10×In)

Setting: Ii = 5~15×In, usually set to 10~12×In to avoid the peak current during motor startup

3.3 Special Significance of 4-pole Protection

Suitable for TN-S and TN-C-S systems, providing overcurrent protection for the neutral line (N line)

When three-phase unbalance or single-phase ground fault occurs, the neutral line current may reach the phase current level, and the 4-pole design can effectively cut off the fault current

Comply with the protection requirements of IEC 60364 standard for three-phase four-wire systems

4. Guide d'installation et de câblage

4.1 Préparation de l'installation

1. Safety Requirements: The power supply must be cut off and locked before installation to prevent electric shock
2. Cabinet Requirements: Reserve sufficient installation space (width × depth × height: approximately 600mm × 800mm × 1000mm)
3. Méthode de fixation: Fix on the distribution cabinet mounting beam with M12 bolts, torque 70N·m

4.2 Câblage du circuit principal (4P.)

4.3 Control Circuit Wiring

Auxiliary Power Supply: AC/DC 220V (operating power supply for ETU35WT)

Contacts auxiliaires: 2 sets of normally open (NON) + 2 sets of normally closed (Caroline du Nord), rated current 5A/250V AC

Trip Signal: Normally closed contact (opened when tripped) for remote alarm

Control Buttons: Closing button (green), tripping button (red), need to be connected to 24V DC or 220V AC control power supply

5. ETU35WT Trip Unit Setting Steps
6. Enter Setting Mode: Press the “Setting” button on the ETU panel and enter the password (default 0000)
7. Overload Long-time Delay (Ir): Set to the rated current of the protected equipment (par ex., if motor In = 1600A, set Ir = 1600A)
8. Short-circuit Short-time Delay (Isd): Set to 5~8×Ir (par ex., Isd = 8×1600 = 12800A), time 0.2s
9. Instantaneous Short-circuit (Ii): Set to 10~12×In (par ex., Ii = 10×1600 = 16000A)
10. Save Parameters: Press the “Confirm” button to save, the ETU will automatically exit the setting mode
11. Function Test: Perform simulated overload and short-circuit tests to verify the correctness of the trip action
12. Fault Diagnosis and Maintenance Guide

6.1 Common Fault Troubleshooting Table

6.2 Maintenance Cycle and Content

7. Selection and Application Scenarios

7.1 Scénarios applicables

1. Industrial Plants: Three-phase four-wire power distribution systems requiring neutral line protection
2. Data Centers: Power supply for critical loads, requiring high reliability and selective protection
3. Bâtiments commerciaux: Power supply for large equipment such as central air conditioners and water pumps
4. Nouveau champ d'énergie: Output side protection of photovoltaic inverters and energy storage systems

7.2 Points de sélection

1. Courant nominal: Select according to the calculated load current (In ≥ 1.25×calculated load current)
2. Capacité de coupure: Select according to the system short-circuit current (Icu ≥ maximum system short-circuit current)
3. Pole Number Selection: Select 3P for three-phase three-wire systems, 4P for three-phase four-wire systems
4. Mounting Type: Select F for fixed mounting, select W (withdrawable) for online maintenance requirements
5. Trip Unit Selection:

Select ETU35WT (LSI) for basic protection

Select ETU37WT (LSIG) for ground fault protection requirements

Select ETU45WT (with communication function) for advanced applications

8. Recommended Accessories and Ordering Information

Ordering Model: 3WT2M40 ETU35WT F-4P

Alternative Model: Withdrawable version 3WT2M40 ETU35WT W-4P

Siemens SENTRON 3WT series air circuit breaker inherits German manufacturing technology, provides reliable power distribution protection solutions, is widely used in various industrial and commercial fields, and is an ideal choice to ensure power supply continuity and equipment safety.