In the withstand voltage testing, if the discharge occurs between conductors, NG by the conductor proximity can be found. Generally, it is said that 1mm discharge in air occurs at 3000V. However, this voltage exceeds the withstand voltage of commonly used connectors and wires. The discharge may occur even if there is no defect. When withstand voltage testing is performed at the test voltage of 1000 V, the distance of discharge that can be found is about 0.3 mm. This distance depends on the shape of the tip of the conductor.Stable detection is considered impossible.