The basis for grounding electric motors to protect them from lightning strikes

\"Code for Design of Electrical Installations in Explosive and Flammable Environments\" (GB50058-92): Article 2.5.15 The grounding design in explosive gas environments shall meet the following requirements. I. The following parts that, according to the relevant technical regulations for the grounding design of electrical equipment, do not require grounding, shall still be grounded in explosive gas environments: 1. The normally uncharged metal enclosures of electrical equipment with an AC rated voltage of 380 V or less and a DC rated voltage of 440 V or less, when located on poorly conductive surfaces ； 2. The normally de-energized metal enclosure of electrical equipment in a dry environment, with an AC rated voltage of 127 V or less and a DC voltage of 110 V or less ； 3. Electrical equipment installed on a grounded metal structure. II. In explosive hazardous environments, the metal enclosures of electrical equipment shall be reliably grounded. All electrical equipment in Zone 1 of explosive gas environments, as well as other electrical equipment in Zone 2 of explosive gas environments except for lighting fixtures, shall be equipped with dedicated grounding wires. If this ground wire is laid in the same protective conduit as the phase wire, it must have the same insulation as the phase wire. At this time, metal pipelines and the metal sheaths of cables in explosive gas environments can only be used as auxiliary grounding wires. In explosive gas environment Zone 2, lighting fixtures may use a metal piping system with a reliable electrical connection as the grounding wire, but pipes used for transporting flammable substances shall not be used. III. The grounding main conductor shall be connected to the grounding electrode in no fewer than two locations in different directions within the explosion-hazardous area. IV. The grounding system for electrical equipment and the grounding system for separate lightning rods designed to protect against direct lightning strikes should be installed separately; however, they can be combined with the grounding system of the lightning rods installed on buildings to prevent direct lightning strikes ； It can also be installed together with grounding devices for protecting against lightning induction. The grounding resistance value should be the lowest one among them. Article 3.4.7 The grounding design for explosive dust environments shall meet the following requirements. I. In accordance with the relevant technical regulations for the grounding design of electrical equipment, the following parts that are not required to be grounded shall still be grounded in explosive dust environments: 1. The normally uncharged metal enclosures of electrical equipment with an AC rated voltage of 380 V or less and a DC rated voltage of 440 V or less, when located on poorly conductive surfaces ； 2. The normally de-energized metal enclosure of electrical equipment in a dry environment, with an AC rated voltage of 127 V or less and a DC rated voltage of 110 V or less ； 3. Electrical equipment installed on a grounded metal structure. II. The metal enclosures of electrical equipment in explosive dust environments shall be reliably grounded. All electrical equipment in Zone 10 of explosive dust environments shall be equipped with a dedicated grounding wire; if this grounding wire is installed in the same protective conduit as the phase wires, it must have the same insulation level as those phase wires. The metal sheath of cables and metal pipelines serve only as auxiliary grounding wires. For all electrical equipment in Zone 1l of explosive dust environments, metal pipes or metal components with a reliable electrical connection can be used as grounding wires; however, pipes used for transporting substances prone to explosion shall not be used. III. To improve the reliability of grounding, the grounding main conductor should be connected to the grounding electrode in at least two locations in different directions within the explosion-hazardous area. IV. The grounding system for electrical equipment and the grounding system for separate lightning rods designed to protect against direct lightning strikes should be installed separately; however, they can be combined with the grounding system of the lightning rods installed on buildings to prevent direct lightning strikes ； It can also be installed together with grounding devices for protecting against lightning induction. The grounding resistance value should be the lowest one among them. Article 4.3.9 The grounding design in fire-hazardous environments shall meet the following requirements: 1. The metal enclosures of electrical equipment in fire-hazardous environments shall be reliably grounded. II. The grounding main wire shall be connected to the grounding electrode at no fewer than two points.