Reasons for the circuit breaker in the switchgear to trip

The tripping of the circuit breaker in the switchgear is a common fault in the power distribution system, usually caused by 

**overload, short circuit, leakage, abnormal voltage or problems with the equipment itself**. The following are the **classification

 of core causes and troubleshooting methods**:

I. Overload Tripping

**Cause**: The load current exceeds the rated current of the circuit breaker.

**Characteristics**:

- The surface of the circuit breaker heats up after tripping.

- There is a burnt smell from the circuit or equipment.

**Common Scenarios**:

- Multiple high-power devices are started simultaneously (such as motors, heaters).

- The aging of the circuit leads to an increase in resistance and abnormal current.

**Troubleshooting Methods**:

1. Use an ammeter to measure whether the loop current exceeds the rated value of the circuit breaker.

2. Check whether the load exceeds the capacity of the circuit.

II. Short Circuit Tripping

**Cause**: The phase wire is in direct contact with the neutral wire/ground wire, or the insulation is damaged, resulting in a 

sudden increase in current.

**Characteristics**:

- There are arcs and explosion sounds when tripping.

- The circuit breaker disconnects quickly (within 0.1 seconds).

**Common Scenarios**:

- The insulation layer of the wire is damaged, and there is a short circuit inside the equipment (such as the burning of the motor winding).

- Small animals enter the switchgear by mistake, causing a short circuit of the phase wire.

**Troubleshooting Methods**:

YouTube：https://youtube.com/shorts/x7syDxzOHhE 

1. Use the low resistance range of a multimeter to measure the resistance between phases/ground of the circuit.

2. Disconnect the loads section by section and gradually troubleshoot the short circuit point.

III. Leakage Tripping (Only applicable to circuit breakers with leakage protection)

**Cause**: The current flows into the ground through an unexpected path (such as electric shock to a person, damage to the 

insulation of the equipment).

**Characteristics**:

- The test button of the residual current device (RCD) pops out.

- It trips again immediately after closing the switch after tripping.

**Common Scenarios**:

- The insulation of the circuit decreases in a humid environment (such as basements, outdoor equipment).

- The metal shell of the equipment is not grounded or the grounding is poor.

**Troubleshooting Methods**:

1. Use a megohmmeter to measure the insulation resistance of the circuit to the ground (should be > 0.5MΩ).

2. Check whether the equipment is reliably grounded (in the TN system, the continuity of the PE wire needs to be checked).

 IV. Abnormal Voltage Tripping

**1. Under-voltage/Over-voltage**

- **Cause**: The fluctuation of the grid voltage exceeds the allowable range of the circuit breaker (such as < 0.85Un or > 1.1Un).

- **Applicable Circuit Breakers**: Intelligent circuit breakers with voltage protection function.

- **Troubleshooting**: Use a voltmeter to measure whether the incoming line voltage is stable.

**2. Phase Loss**

- **Cause**: One phase in the three-phase circuit is disconnected, resulting in the motor stalling and the current increasing.

- **Characteristics**: The motor makes an abnormal sound, and the circuit breaker trips with a delay.

V. Faults of the Circuit Breaker Itself

**1. Mechanical Faults**

- The tripping mechanism is stuck, and the aging of the spring leads to misoperation.

- **Troubleshooting**: Conduct manual opening and closing tests and observe whether there is any jamming.

**2. Incorrect Setting of Protection Parameters**

- The long-time delay/short-time delay setting current is too small (such as using a 16A circuit breaker to protect a 20A load).

- **Solution**: Recalibrate the protection parameters (refer to the Code for Design of Low-voltage Power Distribution GB 50054).

**3. Aging and Failure**

- The contacts are ablated, and the arc extinguish chamber is damaged.

- **Characteristics**: The contacts turn black after tripping, and there are cracks in the arc extinguish chamber.

VI. Environmental and Installation Problems

VII. Quick Troubleshooting Flowchart

```plaintext

Tripping → Reset Attempt:

  ├─ Can be closed and does not trip again → Instantaneous interference (such as motor starting impact)

  ├─ Trips immediately after closing → Short circuit or serious leakage

  └─ Delayed tripping → Overload or under-voltage

 VIII. Preventive Measures

1. Conduct **preventive tests** regularly: Measure the insulation resistance and verify the protection action value.

2. Follow the **power distribution design specifications**: The rated current of the circuit breaker ≥ 1.25 times the

 calculated current of the load.

3. Adopt **hierarchical protection** for important loads: Use long-time delay for the main switch and short-time delay for

 the branch switches.

According to the above classification, the cause of the tripping can be quickly located. If it involves **high-voltage circuit breakers

** or **complex power distribution systems**, it is necessary to further analyze in combination with the action signals of the relay 

protection devices (such as overcurrent, zero-sequence current alarms).