What should be done if the neutral line current is too large?

As we all know, if an electrical line exceeds its rated load, it will overheat severely, and may even cause a fire. For safety reasons, overcurrent protection devices are therefore installed on lines. Whenever the current in the line exceeds the rated value, the overcurrent protection device will automatically cut off the line to prevent fire. The "excessive neutral line current" mentioned here refers to the phenomenon where the neutral line current is excessively high (more than 1.5 times the phase line current) even when the three-phase load is balanced. In such cases, phenomena such as overheating of the neutral line, tripping, and overheating of the transformer usually occur.

It should be noted that electrical codes explicitly prohibit the installation of protection devices on the neutral line. This means that even if the neutral line current exceeds the phase line current, no protection measures will be triggered, and the neutral line will continue to heat up unchecked. Before the overcurrent fuse on the phase line reacts, the neutral line may have been severely overheated and burned out, which could even lead to a fire. When the neutral line is disconnected, electrical equipment on the power grid may be damaged.

In general buildings, the cross-sectional area of the neutral line does not exceed that of the phase line, and is even smaller than the phase line. Therefore, if the current on the neutral line exceeds that on the phase line, overheating will occur, posing a huge safety hazard. Here is a key statistic: the maximum current on the neutral line can reach 1.73 times that of the phase line. According to the formula P=I^2R, the power consumption of the neutral line will be 1.73^2 ≈ 3 times that of the phase line. Such high power consumption will inevitably cause the neutral line to overheat—one consequence is that the neutral line may be burned out, and an even more serious consequence is that it may cause a fire.

Hazards of Excessive Neutral Line Current

Causes the neutral line cable to overheat, accelerating insulation aging and even breaking down the insulation to cause a short circuit, increasing the risk of fire.

• The neutral line current circulates inside the transformer, reducing the transformer's capacity and increasing its losses, causing the transformer to overheat severely and potentially burn out in extreme cases.
• Long-term overcurrent in the neutral line will burn it out, and the system voltage may rise from 220V to 400V, resulting in the burnout of equipment.
• Causes neutral point drift, resulting in a voltage between the neutral line and the ground, endangering equipment and personal safety.
• Causes switches to trip frequently and irregularly, affecting the stability of power supply.
• Increases losses and heat generation of equipment and materials in the power supply system, accelerates insulation aging, and shortens their service life.