Grounding and zeroing

Protective grounding refers to connecting the metal shell of the equipment to the earth, and protective grounding refers to connecting the metal shell to the neutral line. This is very important. You must not be careless when working on a project. There are many specific advantages and disadvantages online, so I won’t list them here: L Haha

Strictly speaking it's not the same thing: ”The "zero" in "connect to zero" refers to the neutral wire. When the neutral wire is broken and the live wire is normal, and the power switch is on and there is a load, the neutral wire becomes the live wire, carrying 220V electricity, which is very dangerous at this time - it is easy to cause electric shock, so it is generally not used to connect to zero. In comparison, grounding is much safer than connecting to zero! ground: In the power system, a good electrical connection using a conductor between the neutral point, shell or bracket of the equipment and electrical device and the grounding device is called grounding. Grounding is divided into working grounding, protective grounding and repeated grounding. Connect to zero: Connecting the metal shell of electrical equipment and electrical devices to the system neutral line is called zero connection. The neutral line includes the working neutral line and the protection neutral line. Generally in AC systems, the neutral line is drawn from the neutral point ； ①TT system: The three-phase four-wire power supply system is a protective grounding system. If the neutral point on the power supply side is grounded, its grounding resistance is large, which is safer. At this time, it is a small grounding current system. When the ground is short-circuited, the remaining two phase-to-ground voltages become larger, between 220 and 380V. However, when the equipment is operating normally, its shell is not connected to the three-phase unbalanced current and voltage of zero protection. This is the main advantage of the IT system. For safety reasons, IT systems are often used in conjunction with leakage protection and zero-break protection. ②IT system: The three-phase three-wire power supply system is a protective grounding, and the individual point on the power supply side is insulated from the ground. Or grounded through high impedance. When a single-phase case is grounded, the contact voltage is easily controlled within a safe value. ； While ensuring the safety of people and equipment, electrical equipment can still work normally. The leakage current value of this system will not be very large, and the protection device cannot be activated in time. Since this system does not have zero-off protection, it cannot set the neutral line N, so it cannot obtain 220V voltage for lighting. This is its shortcoming. When one phase touches the ground, the voltage of the other two phases is 380V, which is more dangerous to the human body. ③TN-C system: The three-phase four-wire power supply system is a protected zero connection. The neutral point on the power supply side is grounded, the grounding resistance is very small, and it is a high-current grounding system. The system's protective neutral line and working neutral line share one wire (PEN), which is simple and economical. However, the PEN line cannot be equipped with a fuse, and once the line is disconnected, it will destroy the stability of the system and pose a danger to the human body and equipment. When a single-phase ground fault occurs in this system, the fault current is large, but not as large as the inter-phase short circuit current. Therefore, line protection devices designed with the same short circuit generally cannot cut off the fault line in time. In addition, in addition to the normal three-phase unbalanced current in the neutral line, the PEN line of this system also has high-order harmonic currents that are dangerous to the human body. Therefore, this system is one that does more harm than good.