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Answers to Basic Questions on Lightning Protection and Grounding Safety 1. There are two basic forms of lightning overvoltage: one is direct lightning – also known as a direct strike; the other is lightning induction – also known as induced lightning. 2. Function of a lightning receptor: A lightning receptor is a metal component designed to capture direct lightning strikes, and it must be connected to the grounding system through grounding conductors. 3. Function of the lightning rod: The role of a lightning rod is actually to guide lightning strikes; it is used to protect against direct lightning hits. 4. Types and functions of arresters: Commonly used arresters include valve-type, vent-type (tube-type), zinc oxide, etc. A lightning arrester is used to protect against lightning overvoltage from entering substations or other buildings along power lines, thereby preventing damage to the insulation of the equipment being protected. Zinc oxide arresters are commonly used outside distribution substations, while valve-type arresters are generally used inside. 5. Common lightning protection measures used in factory power transformation and distribution rooms: Lightning rods (or lightning conductors, lightning strips, lightning grids) are used to protect against direct lightning strikes, while surge arresters are employed to prevent lightning waves from invading. 6. Concept of safe current: Safe current refers to the maximum current that a person can escape from upon being electrocuted. The safe current specified in our country is 30 milliamps (50HZ). The safe current is related to factors such as the duration of electric shock, the nature of the current, the path of the current, as well as body weight and health status. 7. Concept of safe voltage: Safe voltage refers to a voltage level that will not cause direct death or disability in humans. The safety extra-low voltage specified in our country is 36 volts. 8. Concept of ground: In electrical terms, ground (or earth) refers to a place with a potential of zero ； This area generally refers to a place about 20 meters away from the location of the ground fault. 9. Contact voltage, step voltage: Contact voltage refers to the voltage relative to ground that is present when a person comes into contact with the exposed conductive parts of equipment that has a ground fault ； Step voltage refers to the potential difference between a person’s feet when walking near a ground fault. 10. Concepts of working ground and protective ground: The grounding carried out to ensure that power systems and equipment can operate properly is called working ground. Grounding carried out to ensure personal safety and prevent indirect electric shock is called protective grounding. For example: the grounding of the transformer’s neutral point, as well as the grounding of lightning receptors and lightning arresters, are types of working grounding. Grounding of the secondary side terminals of the current transformer and grounding of the equipment enclosure are protective groundings. 11. The several methods of protective grounding currently used in our country include: the TN system; the TT system ； IT systems ； Within the TN system, there are three types of protective grounding methods: TN-C, TN-S, and TN-C-S. 12. Equipotential bonding: Equipotential bonding can be divided into main equipotential bonding and auxiliary equipotential bonding. The purpose of this approach is to directly connect the conductive metal objects that a person might come into contact with to the PE wire. Internationally as well as in our country, it is stipulated that a common equipotential connection should be implemented at the point where the power cable enters the building; that is, all metal components and pipes located near this entry point must be connected to the PE wire. In particularly humid areas with electric shock hazards (such as bathrooms), additional equipotential bonding is also required, that is, all metal components and pipes in such areas must be connected to the PE wire as well. 13. When someone is found to be electrocuted, the first thing to do is to find a way to quickly disconnect that person from the power source, before proceeding with other emergency measures.