High-precision workpiece machining is becoming increasingly common. Manual measurement of workpieces is costly in terms of labor and prone to large measurement errors, failing to meet accuracy requirements. High-precision equipment is complex to operate and has low detection efficiency. Therefore, this has led to the development of online measurement equipment. Online measurement equipment is added or installed without significantly altering existing production processes and equipment. This requires the electrical systems of the equipment to be adaptable to various application scenarios. Electrical safety is a critical matter concerning personnel safety, equipment integrity, and the smooth operation of production, and must be given top priority. It requires people not only to prevent various electrical hazards, eliminate potential electrical accidents, and prevent electrical safety incidents, but also to more effectively protect people's lives and property from loss.
Measures to Prevent Common Electric Shock Accidents
Electric shock accidents are common, accounting for the majority of electrical accidents. Therefore, studying and discussing the patterns and preventive measures of electric shock accidents is essential. To effectively prevent electric shock accidents, both technical and organizational management measures are necessary. These can be summarized as follows:
1. Preventing Contact with Live Parts
The most common and frequently used safety measures include insulation, shielding, and safety distances. In terms of preventing electric shock, shielding and safety distances are safety measures to prevent direct contact with live parts. In addition, shielding and safety distances are also safety measures to prevent electrical accidents such as short circuits and ground faults.
2. Preventing Electric Shock from Leaking Electrical Equipment
Protective grounding and protective neutral connection are basic technical measures to prevent indirect electric shock.
3. Protective Grounding
This involves tightly connecting the non-live metal parts of electrical equipment in normal operation to the earth. The principle is to limit the voltage to ground of the leaking equipment within a safe range through grounding, preventing electric shock accidents. Protective grounding is suitable for power grids with ungrounded neutral points, and the grounding resistance of general equipment should not exceed 4 ohms.
4. Protective Neutral Connection
In a 380/220V three-phase four-wire power supply system, the metal casing of the electrical equipment, which is normally not live, is tightly connected to the neutral wire in the power grid. The principle is that when the equipment leaks electricity, the current passes through the equipment casing and the neutral wire, forming a single-phase short circuit. The short-circuit current blows the fuse or trips the automatic switch, thereby cutting off the power supply and eliminating the risk of electric shock. Protective neutral connection is suitable for low-voltage systems with grounded neutral points in the power grid.
5. Using Safety Voltage
The IEC states that, based on the corresponding expected contact voltage and time curve, ventricular fibrillation will not occur in the human body when the contact voltage is no greater than 50V under dry conditions. Therefore, it specifies that extra-low voltage should not exceed 50V, and safety extra-low voltage should not exceed 42V. my country's standard "Safety Electrical Equipment and Automation Voltage" (GB 3805-83) stipulates that the rated safety voltage levels in my country are 42 V, 36 V, 24 V, 12 V, and 6 V, which should be selected based on factors such as the work environment, operator conditions, usage method, power supply method, and circuit conditions. For non-standard online measurement equipment, in addition to the power supply, the control circuit and main circuit of the equipment should prioritize the use of the corresponding safety voltage level. This is a fundamental measure to prevent electric shock accidents and fatalities. A 24V power supply is usually used.
6. Installing Leakage Protection Devices
Leakage protection devices, also known as electric shock protection devices, can immediately issue an alarm signal and quickly automatically cut off the power supply when electrical equipment and lines leak or cause electric shock in a low-voltage power grid, thereby protecting personal safety. Leakage protection devices can be divided into four types according to their operating principles: voltage type, zero-sequence current type, leakage current type, and neutral point type. Among them, voltage type and zero-sequence current type are more widely used. Current-type devices are commonly used in non-standard online measurement equipment and are often used for protection on the power supply side.
7. Rational Use of Protective Equipment
In special non-standard online measurement electrical work, the rational matching and use of insulating protective equipment is of great significance in preventing electric shock accidents and ensuring the safety and health of operators during the production process.
8. Implementing Organizational Measures for Safe Electricity Use
While technical measures are very important in preventing electric shock accidents, organizational and management measures are also indispensable. These include developing electrical safety operating instructions for non-standard online measurement equipment, conducting safety inspections, education, and training for operators, and organizing accident analysis.