When an arc touches insulators which are used in air circuit breakers, ablation gasses are generated and emitted into the arcing space. As well known, ablation gasses may affect the arc characteristics.

 As a first step of our study, we used parallel plate insulators. The fixed electrodes are connected by a copper thin wire which passes between the insulators. When the discharge is started, the arc touches insulators and ablation gas is emitted. We tested the 10 kinds of polymer insulators.

 We measured current and arc voltage. Using those data, we compared the number of current cycles, voltage wave form, and arc conductance, arc time constant, arc loss. In addition, appearance of the arc is observed by using high speed camera, and we compared the length of emitted gas.