Nowadays the phase controlled switching is a preferred method for capacitive switching.Thus the distribution of pre-breakdown gaps is an important issue for the control strategy.The objective of this paper is to understand the distribution of pre-breakdown gaps for the contact materials manufactured by casting preparing technology in the capacitive service condition of 40.5 kV vacuum circuit breakers（VCBs）.In the experiment

CuCr40 contacts with a diameter of 50 millimeters are prepared by casting technology respectively.L-C oscillating circuit generated inrush current with a frequency of 207 Hz and with a peak of 6.48 kA

while the applied voltage was 46.3 kV which is equivalent to the peak voltage for a 35 kV three-phase network whose capacitive voltage factor is 1.4.The experimental results show that the complementary cumulative probability of the pre-breakdown gap dpre follows the 3-parameter Weibull distribution.The prebreakdown gap below which pre-breakdown would always occur is similar for all three test VIs（Vaccum interrupters） which is 1.6～1.9 mm

and the scattering of the prebreakdown gaps is different which is 3.4～6.0 mm

too.It means the distribution of pre-breakdown gaps for all three VIs significantly varies with closing operations.Thus the distribution of prebreakdown gaps is important when employing phase controlled switching in VCBs for the capacitive switching.