Restriking phenomena in vacuum switches after interrupting is seriously concerned by both manufacturers and utilitites. Measurements show that vacuum switches are with significant bouncing of contacts during open operation. The contacts clearence gaps vary between 2/3-3/2 of their normal stationary value. Experiments show that the periods of the contacts bounce to their minimum gap value are in line with the frequently occurence of the restriking. The paper introduces a laser-optic fiber senser with moire fringe

with which the contact travel charac-teristics of home made vacuum switches of 6

10kV are measured and presented.