... , apply voltage of 750V between phase and phase and between phase and outer sheath,it should be able to withstand for 90min ... without breakdown.Class B, bun in fire with flame temperature 750-800°C, apply voltage of 750V ... 100m, then the insulation resistance≥ 10000MΩ;(5) Power frequency withstand voltage: apply voltage of 2,000V and 2,500V between phase and phase ...