In practical work, some beginners will simply think that the zero line is the ground line, and the difference between the PE line and the PEN line often used in the power system is not very well understood. In the low voltage installation, maintenance and repair, all the above protective wiring of household appliances are often confused, causing the electrical protection wiring to be chaotic and wrong, causing unnecessary trouble, and even causing electric shock accidents. Therefore, the small editor will introduce the meaning of various "lines" in the 380V/220V power system for reference.

Line

The phase line, commonly known as the fire line, is relative to the neutral line (zero line), and refers to any one of the three phase lines L1, L2, and L3 in the three-phase AC circuit. In general, household electricity is only used for three-phase power. One phase, the voltage of phase to ground (neutral line) is 220V, which is called phase voltage. It is composed of a neutral circuit and a current, which makes the current work through household appliances. The voltage between the phase lines of different phases is 380V, called line voltage. Typically, L1, three in three-phase circuit phase L2, L3 use yellow, green and red color sign.

Neutral line

In the three-phase four wire system or the three-phase five wire low voltage power supply system, the neutral line is also called the middle line, the zero line, the working zero line, the N line, and the line is marked with black. Normally, the neutral line refers to a line drawn from the neutral point of the transformer. In the grounding grid, the neutral point of the transformer must be grounded, and the grounding resistance is generally not more than 4 Omega.

The function of the neutral line is to keep the phase voltage of the three-phase asymmetrical load connected by a star to be symmetrical. For a three phase symmetric load, the neutral line can be omitted because the neutral line current is zero. The load for asymmetry, due to the existence of neutral line current, there must be a neutral line voltage of the three-phase load balance, otherwise, three-phase asymmetric load voltage of each phase is not equal (balance), the smaller the load impedance is low voltage, large impedance phase the load voltage is high, easy to cause damage to household appliances. Therefore, in the three phase load asymmetrical low voltage power supply system, it is not allowed to install fuses and individually controlled switchgear on the neutral line, and the neutral wire is usually made of steel cored aluminum conductor, so as to avoid the accident of neutral line breaking. The difference between the phase line and the neutral line is that the voltage of the ground is different, the phase to the ground voltage is 220V, and the neutral line to the ground voltage is zero under normal conditions.

Protection line

The protective line (also known as the PE line, the English full name is protecting earthing), is a conductor connected with the earth through a deep buried electrode. That is what we usually call the ground wire. It is a conductor specially designed to expose the conductive part of the power device.

The protection line can be divided into working grounding wire and protective earthing line. In low voltage power system, the connecting line between the neutral point of the transformer and the working grounding body is called the working grounding wire. The connection line between the metal shell of the household electrical appliance and the protective grounding body is called the protective grounding wire, which is expressed in yellow and green two colors. In the TT system, grounding line PE directly connected to the power supply point grounding work independent, also known as PEE line; in TN - C system, the whole system of the PE line and neutral line is one; in TN - S system, the electric appliance is directly connected with the PE line the special low-voltage power supply system used in the PE line, PE line to the public and transformer grounding reliable connection; in the TN - C - S system, the low voltage side of transformer to the user power line between a line, PE line connected to a common neutral line, users point to the electrical power supply into line with public PE line, the PE line is connected with the electric utility line PE.

Protective neutral line

The protection of the neutral line (also known as PEN line protection, neutral conductor), the color is light blue is the vertical interval, PE line and N line conductor and has be made one, protect the line and neutral line function. The TN C system in low-voltage power system combines the PE line and the N line together. The TN C S system connects the PE line and the N line into one line between the low voltage side of the transformer and the user power entry point, and the TN S system separates the line of attack from the whole line. The power supply system uses the PEN line, usually in order to save the data, but reduces the reliability and safety of the power supply. Where conditions exist, low voltage power supply should use TN S system as much as possible, that is to deploy a completely independent PE protection line, rather than a TN C system that bundles N lines and PE lines together. Special reminder: the demand for power supply safety is relatively high, especially where there is a danger of explosion, it is necessary to use TN - S system power supply.