Why does a charged neutral wire in the distribution box indicate a short circuit?

  In a household electrical circuit, the **neutral wire is normally not charged** (its potential is the same as that of the ground).

If the neutral wire is charged, it is usually related to **short circuits, open circuits, or grounding faults**, but **a charged neutral

wire does not necessarily mean there is a short circuit**. The following is a specific analysis: I. The Normal Function of the Neutral Wire The neutral wire (N wire) is a wire drawn from the neutral point of the power source, and its functions are as follows: 1. It forms a loop with the live wire (L wire) to allow the current to do work through the load (such as light bulbs, refrigerators). 2. During normal operation, the potential of the neutral wire is **close to 0V** (at the same potential as the ground), so touching

the neutral wire will not cause an electric shock. II. Common Causes of a Charged Neutral Wire and Its Relationship with Short Circuits Situation 1: Open Circuit of the Neutral Wire (≠ Short Circuit) **Principle**: The neutral wire is broken at a certain point, preventing the current from returning to the power source through the

neutral wire. The neutral wire after the break point is charged in the reverse direction through the **load** (live wire → load →

neutral wire after the break point → charged).

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**Phenomena**: - Electrical appliances cannot work (the circuit is open). - When measured with a multimeter, the voltage of the neutral wire after the break point is **close to 220V** (at the same potential

as the live wire). **Example**: If the neutral wire terminal is loose and falls off, after the light switch is closed, the part of the neutral wire after the break point will

be charged through the light bulb filament (as shown in the following diagram). Situation 2: Short Circuit between the Neutral Wire and the Live Wire **Principle**: The live wire and the neutral wire are in direct contact (without passing through the load), resulting in a **sudden surge

in current**, which triggers the circuit breaker to trip. **Phenomena**: - The circuit breaker trips immediately after closing, and there may be sparks or a burnt smell in the distribution box. - When measured with a multimeter, the resistance between the live wire and the neutral wire is **close to 0Ω**. **Example**: The insulation layer of the wire is damaged, and the live wire and the neutral wire are directly connected Situation 3: Poor Grounding of the Neutral Wire **Principle**: The neutral wire is not reliably grounded, or the grounding resistance is too large, resulting in the potential of the

neutral wire being **higher than 0V**. **Phenomena**: - Electrical appliances can work, but the neutral wire is slightly charged (the voltage is lower than 220V). - The residual current device may trip accidentally. III. How to Distinguish between an Open Circuit and a Short Circuit of the Neutral Wire?

IV. Troubleshooting Steps

1. **Power-off Detection**:   Disconnect the main power supply and use the **resistance range** of a multimeter to measure the continuity of the neutral wire:   - **Infinite resistance**: Open circuit of the neutral wire.   - **Resistance ≈0Ω**: Short circuit of the neutral wire (or short-circuited by other circuits). 2. **Sectional Troubleshooting**:   Starting from the distribution box, check section by section whether the neutral wire terminals and joints are loose, oxidized, or damaged. 3. **Grounding Test**:   Use the **voltage range** of a multimeter to measure the voltage between the neutral wire and the ground wire:   - **Voltage > 0V**: Poor grounding of the neutral wire. V. Summary: A Charged Neutral Wire ≠ Short Circuit - **Short circuit** means a direct connection between the neutral wire and the live wire, manifested as **overcurrent tripping and

the resistance approaching 0**. - **A charged neutral wire** is more commonly caused by **open circuits or grounding faults**, and a comprehensive judgment

needs to be made based on voltage, resistance, and tripping situations. - **Handling Suggestions**: Give priority to checking the tightness of the neutral wire terminals and the insulation of the circuit.

It is recommended that non-professionals contact an electrician.