Reasons for the heating of the neutral wire

The reasons for the heating of the neutral wire are usually related to abnormal current or line problems. The following are the common reasons and corresponding countermeasures:

 I. Main Reasons

1. **Poor Contact**

   - **Phenomenon**: The neutral wire joint is loose, oxidized, or the screws are not tightened, resulting in an increase in contact resistance.

   - **Consequence**: According to Joule's law \(Q = I^{2}Rt\), when the resistance increases, the heating intensifies, which may cause the line to burn out or even lead to a fire.

   - **Inspection Points**: Check whether the connections at the distribution box, sockets, switches, etc. are loose.

2. **Unbalanced Three-phase Load (Three-phase Circuit)**

   - **Phenomenon**: In a three-phase circuit, the load differences among the phases are too large, causing the neutral wire to carry an unbalanced current.

   - **Consequence**: The current in the neutral wire exceeds the design value, and it will heat up due to long-term overload.

   - **Inspection Points**: Use an ammeter to detect whether the three-phase currents are balanced, and adjust the load distribution.

3. **Insufficient Cross-sectional Area of the Neutral Wire**

   - **Phenomenon**: The diameter of the neutral wire is too thin to withstand the normal current.

   - **Consequence**: The resistance increases, and the heating is obvious.

   - **Countermeasure**: Replace the neutral wire with one of the same specification as the live wire (for example, in a household circuit, it is usually 2.5mm² or 4mm²).

4. **Open Circuit or Loose Connection of the Neutral Wire**

   - **Phenomenon**: The neutral wire is broken at a certain point, causing the neutral wire after the break point to be back-powered through the load (for example, if the neutral wire is broken after the light switch, the light will supply power to the neutral wire in reverse through the live wire).

   - **Consequence**: The break point will heat up due to poor contact, and even sparks may occur.

   - **Inspection Points**: Use a multimeter to detect the continuity of the neutral wire in sections.

5. **Leakage or Short Circuit**

   - **Phenomenon**: The live wire leaks electricity to the neutral wire, or the neutral wire is short-circuited with the ground wire.

   - **Consequence**: The additional current causes the neutral wire to heat up.

   - **Inspection Points**: Check whether the insulation layer of the line is damaged, and test it with a leakage protector.

 II. Countermeasure Suggestions

1. **Power-off Inspection**: Cut off the power immediately to avoid danger.

2. **Professional Detection**:

   - Use a multimeter to measure whether the currents of the neutral wire and the live wire are balanced.

   - Check the voltage of the neutral wire to the ground (it should normally be 0V. If it is charged, check for an open circuit or leakage).

3. **Repair Measures**:

   - Re-tighten the loose joints and remove the oxide layer.

   - Adjust the balance of the three-phase load.

   - Replace the too-thin or aged neutral wire.

4. **Safety Tips**:

   - Non-professionals should not operate by themselves, and it should be handled by a certified electrician.

   - The heating of the neutral wire may be a precursor to line aging or faults, and it needs to be checked in a timely manner to prevent fires.

 Summary

The core reasons for the heating of the neutral wire are **abnormal current** or **increased resistance**, which need to be analyzed in combination with specific scenarios. If the heating occurs frequently, it is recommended to comprehensively check the safety of the line, cut off the power first, and contact a professional for handling.