In practical work, some beginners often mistakenly believe that the neutral line is the same as the ground line. They may not fully understand the distinction between the PE (Protective Earth) line and the PEN (Protective Neutral) line commonly used in power systems. During low-voltage installation, maintenance, and repair tasks, confusion often arises regarding the various protective wiring configurations of household appliances. This can lead to errors in electrical protection wiring, causing unnecessary problems or even electric shock accidents. To avoid such issues, this article provides a brief explanation of the different types of "lines" in a 380V/220V power system for better understanding.
Phase Line
The phase line, also known as the live wire, is one of the three phase lines (L1, L2, and L3) in a three-phase AC circuit. In most homes, only one of these three phases is used, and the voltage between the phase and the neutral line is typically 220V, referred to as the phase voltage. The current flows through the appliance via the phase line and returns through the neutral line, completing the circuit. The voltage between two different phase lines is 380V, known as the line voltage. In three-phase systems, the L1, L2, and L3 lines are usually color-coded yellow, green, and red, respectively.
Neutral Line
In a three-phase four-wire or five-wire low-voltage power supply system, the neutral line is also called the neutral conductor, working zero line, or N line. It is typically marked with black. The neutral line is drawn from the neutral point of the transformer, which is grounded to ensure safety. The grounding resistance should generally not exceed 4 ohms. The primary function of the neutral line is to maintain balanced phase voltages in an unbalanced three-phase load. If the load is symmetrical, the neutral current is zero, and the neutral line can be omitted. However, in an unbalanced load, the neutral line helps balance the voltage across the phases, preventing damage to appliances due to unequal voltage distribution. For this reason, fuses or switches should not be installed on the neutral line, and it is usually made of aluminum-cored steel wire to prevent disconnection.
Protection Line
The protection line, or PE line, is a wire connected to the earth through a deep electrode, commonly known as the ground wire. Its main purpose is to connect the exposed conductive parts of electrical equipment to the ground, ensuring safety in case of faults. The PE line can be divided into a working ground and a protective ground. In the TT system, the PE line is directly connected to a separate grounding electrode, while in the TN-C system, it is combined with the neutral line. In the TN-S system, each device is connected to a dedicated PE line that is reliably grounded at the transformer. In the TN-C-S system, the PE and neutral lines are combined up to the user's incoming point, after which they are separated.
Protection Neutral Line
The protection neutral line, or PEN line, is a conductor that combines both the protective earth and the neutral functions. It is typically marked with a light blue stripe. In the TN-C system, the PE and N lines are combined throughout the system, while in the TN-C-S system, they are combined up to the user’s incoming point. In the TN-S system, the PE and N lines are completely separated. While using a PEN line can save materials, it reduces the reliability and safety of the system. Therefore, it is recommended to use the TN-S system wherever possible, ensuring a separate and reliable PE line.
Difference Between PE and N Lines
The N line (neutral) is essential for maintaining voltage balance and transmitting power, especially in single-phase systems. Without it, many devices would not function properly. On the other hand, the PE line is not necessary for the operation of the device itself but plays a critical role in safety by protecting users from electric shocks in case of faults. Despite its importance, many users overlook the PE line, especially in areas where it is not always properly installed. This can create serious safety risks, particularly when using Class I appliances that require a grounded connection. It is crucial to pay attention to proper grounding to ensure safe and reliable electrical operation.
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