How does the neutral wire of a transformer come about?

The neutral wire of a transformer is an important part of the power system, which is used to provide 

single-phase circuits and safe grounding. Its formation and functions are as follows:

 I. The Source of the Neutral Wire

1. **Emanating from the Neutral Point of the Transformer**

   - The secondary windings of a transformer usually adopt the **star connection method (Y connection)**

. The ends of the three windings are connected together to form the **neutral point**.

   - The wire drawn from the neutral point is the **neutral wire (Neutral Line)**, which is connected to the

 earth through a grounding device.

2. **Grounding Method**

   - The neutral point needs to be directly connected to the earth through a **grounding electrode** 

(such as a deeply buried metal rod) to ensure that the potential of the neutral wire is always zero.

II. The Functions of the Neutral Wire

1. **Providing a Single-Phase Load Circuit**

   - Single-phase devices (such as lighting fixtures and sockets) form a circuit through the phase wire

 and the neutral wire, and the current returns to the power source through the neutral wire.

2. **Balancing Three-Phase Voltages**

   - When the three-phase load is unbalanced, the neutral wire carries the unbalanced current, preventing

 the voltage at the neutral point from shifting and ensuring the stability of the voltages of each phase.

3. **Safety Protection**

   - As **working grounding**, the neutral wire can reduce the voltage to the ground when the equipment 

leaks electricity, and cooperate with the residual current device (RCD) to ensure personal safety.

III. The Differences between the Neutral Wire and the Ground Wire

IV. Precautions

1. **The Neutral Wire Should Not Be Disconnected**

   - If the neutral wire breaks, when the three-phase load is unbalanced, the neutral point will shift, 

resulting in an increase in the voltage of some phases (which may burn out the equipment).

2. **Avoid Mixing the Neutral Wire and the Ground Wire**

   - After entering the house, the neutral wire and the ground wire need to be strictly separated (such as in

 the TN-S system), otherwise it may cause electric shock or equipment failure.

3. **Requirements for the Grounding Resistance**

   - The grounding resistance of the neutral point needs to comply with the specifications (usually ≤ 4Ω)

 to ensure that the fault current can be effectively conducted into the earth.

 V. Summary

- **Source of the Neutral Wire**: Drawn from the neutral point of the secondary winding of the transformer

 and grounded.

- **Core Functions**: Providing a single-phase circuit, balancing voltages, and ensuring safety.

- **Key Requirements**: Reliable grounding, avoiding disconnection, and distinguishing between the neutral

 wire and the ground wire.

In actual operation, it is recommended that professional electricians carry out the design and construction 

according to local power distribution standards (such as the TN-C or TN-S systems in China).