In the process of using the distribution box, more or less, there will be some faults, especially for the distribution box after a long time of use. Here we will introduce the causes of the failure of the distribution box from three aspects:

1. Fault caused by the influence of ambient temperature on low voltage apparatus

The low voltage apparatus in the distribution box is composed of fuse, AC contactor, residual current operated protector, capacitor and metering meter. These low-voltage electrical appliances are designed and manufactured in accordance with the basic standard for low-voltage electrical appliances (GB 1497), and their normal working conditions are specified accordingly: the upper limit of ambient air temperature shall not exceed 40 ℃; the average value of ambient air temperature for 24h shall not exceed 35 ℃; the lower limit of ambient air temperature shall not be lower than - 5 ℃ or - 25 ℃.

The distribution box of rural power network transformation operates outdoors. It not only generates high temperature by direct sunlight, but also generates heat during operation. Therefore, in the high temperature season in summer, the temperature inside the box will reach above 60 ℃, and the temperature at this time greatly exceeds the environmental temperature specified by these electrical appliances. Therefore, the failure caused by overheating of electrical components in the distribution box will occur.

2. Failure caused by product quality

In the transformation of rural power network, due to the large number of distribution boxes and the short construction period, the distribution box factory needed the supply of low-voltage electrical appliances in a short time, which led to the phenomenon that the requirements for product quality were not strict, resulting in the failure of some products shortly after they were put into operation. For example, some types of AC contactors can not run because of the burning of the closing coil of the contactor shortly after the distribution box is put into operation.

3. Failure caused by improper selection of electrical appliances in distribution box

Because the capacity selection of AC contactor is not appropriate during manufacturing, AC contactor with the same capacity is installed for different outlet circuits, and the unbalanced situation of three-phase load is not considered, and the current level of some outlet contactors can not be improved by a current level selection based on the normal model selection, which leads to AC contactor burnout during operation in high temperature season in summer situation.