In the construction (renovation) of rural power grids, the operating environment of the low-voltage distribution boxes of newly built distribution transformers has changed significantly, from indoors to outdoors. Therefore, the low-voltage electrical appliances selected in the distribution boxes will be affected by the weather during operation. In the first phase of the renovation project in our province, about 50% of the distribution boxes have been put into operation. According to the feedback from various regions, although the weather has not yet reached the high-temperature season, the residual current operated protective devices in the distribution boxes have already experienced different types of faults, such as: (1) transformer contactor faults; (2) residual current operated protective device faults; (3) faults caused by internal wiring; (4) metering energy meter faults; (5) faults caused by burnt fuse bases and motor burnout due to phase loss, etc. Now, I will discuss some views on the faults of distribution boxes. 1. Faults caused by the influence of ambient temperature on low-voltage electrical appliances The low-voltage electrical appliances in the distribution box consist of fuses, AC contactors, residual current operated protective devices, capacitors, and meters. These low-voltage electrical appliances are all designed and manufactured according to GB1497 "Basic Standards for Low-Voltage Electrical Appliances," which specifies their normal operating conditions: the upper limit of ambient air temperature shall not exceed +40℃; the average ambient air temperature over 24 hours shall not exceed +35℃; and the lower limit of ambient air temperature shall not be lower than -5℃ or -25℃. Distribution boxes in rural power grid upgrades operate outdoors, exposed to direct sunlight and generating heat during operation. Therefore, in the hot summer months, the temperature inside the box can reach over +60℃, significantly exceeding the ambient temperature specified in the national standards for these appliances, thus causing malfunctions. ① Most low-voltage electrical appliances use Class A insulation, with a maximum permissible temperature rise of 65℃ during long-term operation. The high temperature inside the distribution box makes it difficult for the internal heat of the low-voltage electrical appliances to dissipate, leading to insulation aging and burnout over time; the plastic-insulated wires will also age and break down due to heat. ② Electronic products inside the distribution box, such as residual current circuit breakers and electronic meters, will have their lifespan severely affected when operating at high temperatures. This also impacts the stability of the protector's performance, the reliability of its operation, and the accuracy of its measurement. ③ Reactive power compensation capacitors and fuses operating at high temperatures will also have their lifespan shortened. 2. Faults caused by some manufacturers neglecting product quality During rural power grid renovation, the large number of distribution boxes required and the short construction period necessitate urgent and large-volume deliveries of low-voltage electrical appliances by distribution box manufacturers. Consequently, they neglect strict quality control requirements, resulting in some products malfunctioning shortly after being put into operation. For example, some manufacturers rushed to produce electricity meters that failed to operate normally after installation in distribution boxes, and contactor closing coils burned out after a short period of operation. 3. Adverse consequences of price reductions after price limits were imposed on distribution boxes When budgeting the cost of distribution boxes, relevant departments conducted a preliminary investigation into the prices of low-voltage electrical appliances and raw materials used in the boxes and allowed a certain margin when setting price limits. However, some functional departments, while maintaining price limits, pressured the manufacturers to lower the price of distribution boxes by 200 to several hundred yuan per box. Due to this price pressure, manufacturers, driven by their own interests, were forced to use cheaper, lower-quality low-voltage electrical appliances to make the distribution boxes. Therefore, those making the decisions did not consider that these distribution boxes would become fixed assets of their units, and they would have to bear the future maintenance costs. For example, AC contactors of the same brand and capacity can differ in price by tens of yuan. After the price reduction, electrical manufacturers resorted to cutting corners, reducing costs by using inferior materials for the closing coil and main contacts. Some materials even had a maximum allowable temperature rise of only 45°C, severely impacting the durability of the main contacts. Residual current operated protective devices with similar performance and capacity, despite being safety-certified products, showed significant differences in quality during actual use. To reduce costs, some manufacturers do not produce products using the components and circuit designs selected during safety certification. For example, the auxiliary power transformer in the protector: some manufacturers design it as 3VA, while others design it as 5VA. A 3VA transformer is definitely more prone to burnout and has a shorter lifespan. 4. Several suggestions: ① If space permits, a temperature control relay and exhaust fan should be installed so that the exhaust fan automatically starts when the internal temperature reaches a certain value, forcibly dissipating heat. ② Spray a heat-insulating chemical coating on the inner wall of the distribution box to reduce heat radiation and lower the internal temperature. ③ Appropriately enlarge the size of the distribution box to increase the electrical safety distance between branch lines and between the lines and the box casing. This facilitates operation, maintenance, and fuse replacement for rural electricians, and also improves heat dissipation. ④ Strictly control the selection and acceptance of low-voltage electrical appliances, and carefully select appropriate AC contactors. Carefully select protective devices: Residual current operated protective devices (RCDs) are not only crucial for the reliable operation of distribution boxes but also a primary technical measure to prevent electric shock accidents. Therefore, relevant departments must not select devices based solely on price but rather on quality and optimal selection. ⑤ It is recommended that the connecting wires inside the distribution box have sufficient current carrying capacity. For example, the incoming lines of distribution boxes for 30kVA and 50kVA transformers should be no less than 35mm² wire, and the branch lines no less than 25mm² wire; the incoming lines of distribution boxes for 80kVA and 100kVA transformers should be no less than 50mm² wire, and the branch lines no less than 35mm² wire. In short, the current carrying capacity of the wires must be greater than that of the indoor distribution box because of the different ambient temperatures.