What are the reasons why the neutral wire is electrified but electrical appliances can still be used

YouTube：https://youtube.com/shorts/lbdp6KFUzvM

1. **Unbalanced Three-Phase Load**

- **Principle**: In a three-phase four-wire power supply system (commonly seen in centralized power supply scenarios such as factories and residential communities), under normal circumstances, the vector sum of the three-phase currents is zero, and there is no current passing through the neutral wire. However, when the three-phase load is unbalanced, for example, if too many high-power electrical appliances are connected to one phase, the vector sum of the three-phase currents will no longer be zero, and current will flow through the neutral wire.

- **Example**: Suppose in the three-phase power supply system of a residential community, a large number of air conditioning equipment is connected to Phase A, while the loads of Phase B and Phase C are relatively small. During the peak electricity consumption period in summer, the current of Phase A will be significantly greater than that of Phase B and Phase C. At this time, current will flow through the neutral wire. Since the neutral wire has a certain resistance, according to Ohm's law (U = IR, where U is voltage, I is current, and R is resistance), a voltage drop will be generated on the neutral wire, resulting in the neutral wire being electrified. However, as long as this voltage is within the allowable fluctuation range of the rated voltage of electrical appliances, the electrical appliances can usually still be used normally.

2. **Open Circuit of the Neutral Wire**

- **Principle**: If the neutral wire is broken at a certain position, the current of the loads connected after the break point cannot flow back normally through the neutral wire. At this time, these loads are equivalent to being connected in series to the live wire. Due to the voltage division in series, the neutral wire, which originally served as a return circuit, will become electrified.

- **Example**: For example, in a household electrical circuit, the neutral wire from the distribution box to a certain socket is broken. When an electrical appliance is plugged into this socket, current flows into the electrical appliance from the live wire but cannot flow back through the neutral wire. If a test pen is used to test the neutral wire hole of the socket, it will be found that the neutral wire is electrified. However, for some electrical appliances that are more adaptable to voltage fluctuations, such as some simple resistance heating electrical appliances (like soldering irons), they may still be able to work normally when the neutral wire is electrified as long as the voltage does not exceed their working range.

3. **Inductive Electrification** - **Principle**: The neutral wire and the live wire are laid in parallel. When alternating current passes through the live wire, an alternating magnetic field will be generated around the neutral wire. According to the principle of electromagnetic induction, this alternating magnetic field will induce an electromotive force on the neutral wire, thus making the neutral wire electrified.

- **Example**: In some places with relatively dense wiring, such as inside a power distribution cabinet, the distance between the live wire and the neutral wire is relatively close. When large equipment in the power distribution cabinet starts or stops, the current of the live wire will change significantly, generating a relatively strong alternating magnetic field. At this time, the neutral wire is prone to be inductively electrified. Generally, this induced voltage is relatively low and, in many cases, will not affect the normal use of electrical appliances.

4. **Poor Grounding** - **Principle**: In a normal TN-C or TN-S grounding system, the neutral wire needs to be well grounded. If there is a fault in the grounding device, such as excessive grounding resistance or loose grounding connection, the potential of the neutral wire cannot be stably pulled to the earth potential (zero potential), thus resulting in the neutral wire being electrified.

- **Example**: Taking the grounding system of a factory as an example, if the grounding electrode is corroded over a long period and the grounding resistance increases. When current flows through the neutral wire to the grounding electrode, due to the existence of the grounding resistance, according to Ohm's law, a voltage will be generated on the neutral wire, resulting in the neutral wire being electrified. However, as long as this voltage does not seriously interfere with the normal working voltage of electrical appliances, the electrical appliances may still be able to work normally.