Abstract: With the continuous development of the automobile manufacturing industry and the continuous improvement of human living standards, the demand for cars in the market is also increasing. In order to better implement the concept of “cost saving, cost reduction, and efficiency enhancement” of Beijing Benz, fully reflecting the significant historical significance of “carbon peaking and carbon neutrality”, meantime improving the technical level of employees and testing repaired spare part onsite, body shop maintenance decides to build master piece.Based on actual on-site requirement, the designing of low-voltage electrical cabinets has become an important part of building master piece, it mainly designs and selects specifications for low-voltage circuit breakers, fuses,and power cables, load calculation through the coefficient of demand method, verify the set current of low-voltage circuit breakers and low-voltage fuses, calculate and select power cable specifications through the economic current density method. After selecting components, the article installs them in the electronic cabinet and applies cabinet to body shop master piece, it achieves the test function of repairing spare parts.