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Safety knowledge on insulating equipment 1: What is the difference between insulating boots and shoes and ordinary boots and shoes? Insulated boots and shoes differ from ordinary boots and shoes in design; they feature a border made of insulating rubber material in their structural design, with the insulating layer creating a sealed insulation system to protect the feet. Ordinary boots and shoes are different; their soles and insoles are not made of insulating materials, resulting in very poor insulation properties and a high risk of electric leakage. Some have a leakage current as high as 30 mA, which far exceeds the safe level; therefore, each insulating boot and shoe must undergo electrical performance testing, and only those that pass can be released for sale. Ordinary boots do not have this requirement. 2. Why must insulating protective equipment be worn while kept dry? Wearing insulating protective equipment in a dry state is an important issue that users must pay attention to, as if such equipment contains a certain amount of moisture, its volume resistivity and surface resistivity **decrease**. Water is a conductor; its presence reduces or even destroys the insulating properties of insulators. Since the water molecules have an angular structure with ∠HOH = 105°, which gives them strong polarity and enables them to conduct electricity as ions; moreover, there are many impurities in water that can undergo chemical changes under the influence of heat, light, or electricity, thereby becoming conductors and destroying the insulating properties. Therefore, keeping insulating protective equipment dry can greatly enhance safety. 3. What is the most important indicator of the insulation performance of insulating protective equipment? The purpose of wearing insulating protective equipment (such as insulating boots, shoes, gloves, etc.) is to prevent electric shock injuries, which are mainly caused by electric current passing through the human body. Therefore, the quality of an insulator’s protective properties is determined by the magnitude of the leakage current that passes through it at a certain voltage level; if the leakage current falls within the safe range, it is considered safe, otherwise it is not. If a certain voltage is applied, even if breakdown does not occur, an excessive leakage current can still cause harm to the human body. 4. Why are preventive tests required for insulation protective equipment? Conducting preventive tests is a strict requirement in the power industry to ensure absolute safety for people. Some insulating protective equipment comes with a relatively long warranty period. Over such a long time, changes due to aging or storage conditions can occur; from a safety perspective, it is necessary for users to conduct preventive tests before using such equipment. For insulating boots and shoes, if they are beyond the warranty period, preventive tests can still be conducted; they can only be used after passing these tests. 5. What is the relationship between the test voltage and the maximum operating range? Before leaving the factory, each insulating protective device is tested at a specific alternating current operating voltage; for example, in applications where 5KV is used, the line-to-line voltage is 380V. The test voltage is a safety factor of 13.2 times the operating voltage, but the conditions and environments of use vary, and differences exist among different countries. Referring to the empirical formula from the United States, determine the relationship between the test voltage and the maximum operating range. According to the empirical formula recommended by ASDTMD120-79 in the United States: Maximum voltage = Test voltage × 0.95 – 2000 V. 6. In environments where anti-static protective equipment is required, what else should be taken into consideration after wearing such equipment? An anti-static environment is primarily necessary to prevent static electricity induction caused by charge accumulation resulting from frictional charge flow, or the hazards resulting from high-voltage static discharge. After wearing anti-static protective gear, the accumulated charge can be promptly discharged to ground through this gear. At the same time, it is not advisable to wear underwear and socks made from materials such as fur, as they are insulating and prevent the body’s static electricity from being conducted to ground. (The resistance value of conductive shoes should not exceed 100KΩ–1000KΩ). 7. What is the safe current level that the human body can tolerate? The insulation resistance value of the human body is between 800 and 1000 ohms, but this varies depending on factors such as a person’s weight, thickness of the skin, age, and height; it also differs based on an individual’s physical strength. The standard safe current for mains-frequency alternating current in the United States is 16mA, while China’s standard is 14mA. Under normal circumstances, the human body begins to feel numb at an alternating current frequency of 1 mA or a direct current level of 5 mA. It is possible to break free from the power source at an alternating current frequency of up to 14 mA. However, at alternating current frequencies of 20–25 mA or a direct current level of 80 mA, the body experiences numbness, severe pain, or difficulty breathing; it becomes impossible to get away from the current, and over time this can be life-threatening. 8. What other precautions should be taken while working after wearing insulating boots and shoes? When working as an electrician, it is required to wear insulating boots for insulation protection. However, when the workload is heavy or the weather is hot, it is possible for parts of the body to accidentally come into contact with walls or grounded equipment; in such cases, electric shock can still occur due to leakage current. Therefore, even though insulating boots are worn, it is necessary to prevent other parts of the body from making contact with the ground while working. On rainy days, even if insulating boots or gloves are worn, it is necessary to have the appropriate rain gear. Prevent electric shock to the limbs caused by conductive moisture in insulating protective gear. 9. What is the impact of replacing water with metal balls as the electrode in high-voltage insulating boots under the new national standards on the test results? The new national standard replaces water with metal balls as the internal electrode for testing, in order to align with international standards. The previous national standard testing methods were more stringent than those abroad; using water as the internal electrode for insulating boots reduced their insulation performance due to water intrusion tests, which made such methods unreasonable compared to international standards. Therefore, when testing voltage levels, it is not allowed to use water as the internal electrode, nor is it permitted to conduct tests at voltages higher than those specified for preventive testing. 10. What are the main differences between insulating gloves for live work and rubber insulating gloves for high and low voltage applications? Insulating gloves for live working allow performing work on live circuits within different voltage ranges. High and low voltage insulating gloves are auxiliary safety equipment; working on live circuits is not permitted with them. Insulating gloves for live working shall undergo type tests and sampling tests in accordance with IEC 60903 and GB17622-1998. The test samples are to be pre-soaked at a standard water depth for 16 hours before undergoing voltage testing, which is carried out for 3 minutes; the minimum withstand voltage must be met (the part of the glove above the water level must remain dry). As per the IEC standard for Type 02, the type testing and sampling tests involve first immersing the insulating gloves used for live work at the immersion depth specified in the standard (65 mm from the cuff of the glove to the level at which the voltage is applied for testing, with a minimum withstand voltage of 75 mm). After an immersion period of 16 hours, the voltage is increased to 20 kV at a rate of 3000 V per second; this process is carried out for 3 minutes. If no breakdown occurs and the leakage current remains below 20 milliamps, the test is passed, after which the voltage is immediately reduced and the power is turned off. The minimum tolerance voltage is such that when it reaches 30 kV at the same voltage-raising rate, it is immediately shut down by reducing the voltage. The routine test (required for factory testing) involves testing for 1 minute at verification voltages of different models (no 16-hour immersion required). However, to ensure safety, our company conducts outlet tests for 3 minutes; there are no requirements regarding pre-soaking of high- and low-voltage insulating gloves, nor are there any tests requiring a minimum withstand voltage higher than the test voltage. When purchasing insulating gloves for live working, routine testing and inspection can be carried out according to different models. Whether it is qualified, and whether the leakage current is less than 16 mA (for the specification with a length of 410 mm). 11. Why are cracks found in insulating gloves used for live work during testing? When insulating gloves used for live working are employed in high-voltage tests, arcing can occur between two electrodes under high voltage due to an improper water filling level or because the areas of the glove cuffs that are not submerged in water remain dry. This arcing leads to discharge in the air, producing a buzzing sound; at the same time, it ionizes the air, converting the oxygen present in it into ozone. An increase in ozone concentration causes severe oxidative damage to rubber, leading to cracks and deterioration of the rubber. High-voltage testing is, therefore, a form of destructive testing – each test results in damage to the rubber. Hence, it is necessary to conduct preventive tests during use to ensure the safety of those who operate these gloves.