Abstract: OPPC connector box is an important connection protection device for overhead transmission lines, which plays the role of photoelectric isolation and mechanical connection. In this paper, an OPPC connector box fault is analyzed, and the cause of the fault is judged through experimental tests and disintegration observations, and it is clarified that there are bubbles and local air gaps at the interface between epoxy resin and fiberglass pipe, resulting in uneven distribution of internal electric field, causing partial discharge, and the electrothermal stress generated by partial discharge makes the epoxy resin carbonized, continuously destroys the insulation between epoxy resin and glass fiber pipe, and finally forms a penetrating discharge channel, and the equipment expands and explodes from the inside out due to electrothermal stress.