Effect of an insulation support on breakdown in a non-uniform field is studied. Breakdown voltages and time-to-breakdown, with and without and insulating support, are measured under switching and lightning impulse voltages. The experimental results for breakdown voltages. The experimental results for breakdown voltage and time-to-breakdown, with an insulation support, are found to fit weilbull and log-normal distributions respectively. The influence of an insulating support on the time-to-breakdown is analysed using Von Laue diagrams. The experimental results are interpreted as indicating that an insulating support may have a significant effect on the initiatory electron production. The effect of the over voltage factor on the time-to-breakdown is also discussed.