Which statement best describes the relationship between dry flashover and wet flashover?

• A. A dry flashover happens only in dry climates; a wet flashover happens only during rain.
• B. Dry flashover occurs with no moisture on the surface; wet flashover occurs when moisture enables surface leakage and discharge.
• C. Dry flashover occurs when humidity is high; wet flashover occurs when humidity is low.
• D. Dry flashover and wet flashover are the same phenomenon.

Answer: (B)

Flashover along an insulator surface depends on how conductive the surface is to leakage current. The key factor is surface resistivity, which drops dramatically when moisture is present. Without moisture, the surface remains relatively resistive, so a discharge across the surface needs a much higher voltage to occur. When moisture films the surface, ions from contaminants dissolve in the water and create a continuous conductive path, allowing leakage current to bridge the voltage difference and cause discharge at a lower voltage. That’s why the statement describing dry flashover as happening with no moisture and wet flashover as happening when moisture enables surface leakage and discharge is the best description. The other options either tie flashover to climate, to humidity ranges, or claim they’re the same phenomenon, which doesn’t reflect the essential role of surface conductivity altered by moisture.