j grounding type

The TN-C power supply system uses the working neutral wire as both the neutral wire and the protective wire; it can be referred to as a protective neutral wire, and is denoted by NPE. The TN-S power supply system is one in which the working neutral wire N and the dedicated protective wire PE are strictly separated from each other; it is known as a TN-S power supply system. To ensure safe power supply, it is better to use the TN-S system.

For the TN-S power supply system, it is highly recommended to use a 5-wire system with separate neutral and ground wires in lathe systems in order to ensure the safety of personnel to the greatest extent possible

The TN-S power supply system is safe and reliable, and is suitable for low-voltage power supply systems in industrial and civil buildings.

1. Technical measures for safe electricity use: (1) Protective grounding refers to establishing a reliable electrical connection between the non-live metal casing of electrical equipment and the grounding electrode. Its function is to ensure that when the metal casing of electrical equipment becomes charged, if a person touches this casing, since the resistance of the human body is much higher than that of the grounding conductor, most of the current flows into the ground through the grounding conductor, while only a small amount of current flows through the human body. At this time, by properly controlling the ground resistance (generally not exceeding 4Ω), electric shock accidents can be reduced. However, in TT power supply systems, the voltage on the equipment enclosure of devices using this protection method remains quite dangerous to humans. Therefore, this protection method is only applicable to construction sites with TT power supply systems, where the resistance of the protective grounding is required to be no greater than 4Ω. (2) Protective zero connection: In low-voltage power systems where the power supply neutral point is directly grounded, making an electrical connection between the metal casing of electrical equipment and the neutral wire or a dedicated neutral wire in the power supply system is known as protective zero connection. Its function is to ensure that when the metal casing of electrical equipment becomes charged, the short-circuit current forms a closed circuit through the neutral wire, resulting in a single-phase short-circuit fault. Since the impedance of the neutral wire is very low, the short-circuit current is extremely high, usually several times or even dozens of times the rated current. Such a severe single-phase short-circuit causes the protection device to act quickly and accurately, cutting off the power supply in order to ensure personal safety. Its power supply system is a zero-connected protection system, namely the TN system. Whether the protective neutral is separated from the working neutral allows the TN power supply system to be divided into three types: TN-C, TN-S, and TN-C-S. 1) TN-C power supply system. Its working neutral wire also serves as the grounding protection wire. This power supply system is what is commonly referred to as the three-phase four-wire system. However, when the three-phase load is unbalanced, there is an unbalanced current in the neutral wire; therefore, the metal enclosure of the electrical equipment connected to the protective wire has a certain potential. If the neutral wire is broken, the enclosure of a leakage-proTECTED device connected to ground becomes charged. Therefore, this power supply system has certain drawbacks. 2) TN-S power supply system. It is a power supply system that strictly separates the working neutral wire N from the dedicated protection wire Pe at the power source, also known as the three-phase five-wire system. Its advantage is that there is no current in the dedicated protection wire, which is specifically used to carry fault currents to ensure that the protective device operates. It should be specifically noted that the PE wire must not be disconnected. At the power supply terminal, the PE wire should be grounded repeatedly. 3) TN-C-S power supply system. At a construction site, if a transformer is shared with another entity, or if the neutral point of the transformer at the site is not connected to a PE wire – resulting in a three-phase four-wire power supply – and it is necessary to use a dedicated protection wire PE at the site, then a separate PE wire can be drawn out by performing repeated grounding of the neutral wire in the main electrical panel at the site. Such a system is known as a TN-C-S power supply system. During construction, it should be noted that except at the main panel, the N wire and the PE wire must not be connected anywhere else. Switches and fuses must not be installed on the PE wire, nor should the ground be used as a PE wire. The PE wire must also not enter the leakage protector, because the operation of the leakage protector at the end of the circuit will cause the preceding leakage protectors to activate as well. Whether protective grounding or protective neutralizing is used, it must be noted that in the same system, it is not allowed to ground some equipment while neutralizing another. Because in the same system, if some devices are grounded while others are connected to the neutral wire, then when a grounded device experiences a shell leakage, the potential of the neutral wire will rise, causing the shells of all devices connected to the neutral wire to acquire a dangerous voltage.

The TN-S power supply system is safe and reliable, and is suitable for low-voltage power supply systems in industrial and civil buildings.