In the realm of crane operations, safety is of paramount importance. The safe operation procedures for cranes typically emphasize maintaining a sufficient distance from power lines. However, in the real world of practical operation, especially in confined and narrow spaces, it can be an extremely challenging task to maintain an adequate safe distance. A review of numerous hoisting accident cases reveals that there are a significant number of instances where the crane boom comes into contact with high-voltage lines.
On June 20, a tragic incident occurred in Yuncheng when a crane accidentally touched a high-voltage line, resulting in a fatal outcome. When the crane boom makes contact with a high-voltage line, electricity is conducted through the metal crane boom, electrifying the entire vehicle body. Relevant personnel on the vehicle and in the vicinity will be at risk of being shocked by touch voltage and step voltage respectively. Due to the immense power of high-voltage lines and the high voltage levels involved, those who are shocked are easily severely injured or even lose their lives.
So, is there a more scientific approach that can prevent people from being shocked even if the wire is accidentally touched? The answer is yes. A specific technical measure is to add a temporary grounding protection device to the crane.
The temporary grounding protection device consists of several key components. Firstly, there is the grounding copper wire. This is composed of a multi-strand, high-quality special soft copper wire several meters in length and with a diameter of not less than 25mm. It is also covered with an outer transparent plastic sheath layer. This copper wire is designed to conduct electricity safely to the ground. The multi-strand construction ensures flexibility and durability, while the large diameter allows for a high current-carrying capacity. The transparent plastic sheath provides insulation and protection, preventing accidental contact with the wire and reducing the risk of electrical hazards.
Secondly, there are the connecting wire clips. These are fixed at both ends of the grounding wire and are used to connect the vehicle body and the grounding pile. The wire clips must be of high quality and firmly attach to the respective surfaces to ensure a reliable electrical connection. They are designed to withstand the forces and vibrations that occur during crane operations and prevent accidental disconnection.
Finally, there is the temporary grounding electrode, also known as the grounding pile or rod. This must be a metal cone with a length greater than 120cm and a cross-sectional area greater than 190mm². The large size and metal construction of the grounding pile ensure a good contact with the ground and a low resistance path for the electrical current. The cone shape helps to drive the pile into the ground easily and provides stability.
The specific operation procedure of the temporary grounding protection device is as follows. After the crane selects a position and lowers the outriggers but before lifting, the operator must take certain precautions. Around the crane site, first, a high-quality and solid soil surface should be selected. This is crucial as the quality of the soil affects the effectiveness of the grounding. A sledgehammer is then used to drive the grounding pile into the ground more than 80 centimeters deep. This depth ensures a good connection with the earth and a low resistance path for the electrical current. After the grounding pile is in place, the wire clips at both ends of the grounding wire are fixed to the grounding pile and the vehicle body respectively. The contact part of the vehicle body must be a metal surface without paint. Paint can act as an insulator and block the flow of electrical current. Therefore, it is essential to ensure a clean metal-to-metal contact for effective grounding. After taking these measures, the driver can get on the vehicle and operate with a greater degree of safety. Once the crane operation is completed and the crane boom is in place and put away, the grounding wire can be removed.
After grounding, even if the crane boom accidentally touches the line and conducts electricity, the fault short-circuit current will flow to the ground through the vehicle body via the grounding wire. This keeps the entire vehicle body at the same potential as the earth, greatly weakening the impact of electricity on the human body. The driver getting on and off the vehicle, the ground personnel supporting the hoisted cargo, and other personnel close to the vehicle body will not be in danger of being shocked by the strong touch voltage. This can significantly reduce the fatal threat and thus reduce casualties. At the same time, the grounding wire disperses the fault large current passing through the wheels, which can avoid the fire danger caused by tire explosion and fire and reduce property losses.
However, it must be emphasized that grounding does not mean that one can be careless or reckless during operation. Touching power lines should be strictly prohibited at all times. Even with grounding protection, the potential difference explosion of overhead power lines is equally terrifying. Power grid accidents and power outages are also extremely dangerous, and there is still the threat of step voltage. In addition, if the grounding wire measures are not implemented rigorously, there is still a risk of electric shock. Implementing grounding protection measures is the last protective barrier and should only be considered as a last resort.
When grounding, the following four points should also be carefully observed. Firstly, do not use other metal wires instead of grounding wires. Generally, metal wires other than the specified grounding wire have a low current-carrying capacity. When a short-circuit large current occurs, these wires will be instantly burned off, making the vehicle body return to a high voltage state once again. This can pose a serious threat to the safety of personnel. Secondly, the connection surface of the wire clip should be clean and free of debris. It cannot be fixed on a painted surface as that will block the path of the fault current. The connection point should be compact and firm to ensure a reliable electrical connection. The vehicle body is preferably equipped with a specially set galvanized hanging connection point to avoid unfavorable contact surfaces such as paint. Thirdly, the grounding pile should be selected on a damp and good soil original ground. It must not be placed in a scene of piled loose soil, cement, or stones. Loose soil, cement, and stones can have a higher resistance and may not provide a good grounding connection. Damp soil with good conductivity is ideal for effective grounding. Finally, to avoid possible step voltage, people must stay more than 3 meters away from the temporary grounding electrode, vehicle body, and support. Step voltage is the voltage difference between two points on the ground due to the flow of electrical current through the earth. Staying at a safe distance helps to reduce the risk of being shocked by step voltage.
For example, imagine a construction site where a crane is in operation. In a confined space, the risk of the crane boom coming into contact with high-voltage lines is increased. Without proper grounding protection, if such an accident occurs, the consequences could be disastrous. The people on the crane and nearby could be severely injured or even lose their lives. However, by implementing the temporary grounding protection device and following the correct procedures and precautions, the risk of electric shock can be significantly reduced. The driver and ground personnel can work with greater confidence and safety, knowing that there is an added layer of protection in place.
In conclusion, reducing casualties caused by cranes touching high-voltage lines requires a combination of careful operation, proper safety procedures, and the implementation of effective grounding protection measures. By being aware of the risks and taking the necessary precautions, crane operators and those working around cranes can minimize the potential for accidents and protect lives and property.
