The distinction between high-voltage and low-voltage electrical equipment is primarily based on its operating voltage level. According to the International Electrotechnical Commission (IEC), the dividing line between high-voltage and low-voltage electrical equipment is 1000V AC (1500V DC).
Insulation performance is a fundamental indicator for the safe operation of equipment. The resistance between electrical equipment and the earth through a grounding device is called grounding resistance. Different electrical equipment has different requirements for grounding resistance: transformers or generators with a capacity of 100kVA or more have R≤4 ohms; valve-type surge arresters have R≤5 ohms; independent lightning rods, small grounding current systems, transformers or generators with a capacity of 100kVA or less, and grounding systems shared by high- and low-voltage equipment all have R≤10 ohms.
The grounding resistance of electrical equipment should be tested twice a year, in spring and autumn when rainfall is low, to ensure that the grounding is qualified. Grounding electrodes are generally made of galvanized steel pipes or angle steel, with the top end 0.5–0.8m above the ground and at least 1.5m away from buildings. To ensure personal and equipment safety, all electrical equipment should be protectively grounded in accordance with the national standard GB14050 "Types and Safety Technical Requirements for System Grounding". Grounding resistance is generally tested using specialized instruments (such as the ZC-8 grounding resistance tester), or the ammeter-voltmeter method can be used.