The diameter of suspension porcelain insulator disks varies from 3 3/8 to ?

• A. 8 1/2"
• B. 10"
• C. 11 1/2"
• D. 12"

Answer: (C)

Suspension porcelain insulator disks are sized to handle both electrical stress and mechanical load. The diameter grows as you move to higher-voltage classes because a larger disk surface area helps spread the electric field and increases strength to withstand wind and weight when the disks are stacked in a string. The standard range starts at 3 3/8 inches and goes up to 11 1/2 inches for the larger disks. This is why 11 1/2 inches is the correct upper limit. Smaller diameters shown are typical of lower-voltage designs, and 12 inches isn’t a standard size for these disks.