Among common insulation materials listed, which is least commonly used for electrical cables today?

• A. PVC
• B. Rubber
• C. Glass
• D. Wood

Answer: (D)

The key idea is dielectric and environmental suitability for insulation around conductors. The insulating material must provide good electrical insulation (high dielectric strength), resist moisture, tolerate operating temperatures, and remain mechanically stable and safe under flame conditions.

PVC is widely used because it can be extruded into a uniform layer around a conductor, offers solid dielectric strength, moisture resistance, and good fire performance at a low cost. Rubber is also common, providing flexibility and adequate insulation for many flexible cables and cords.

Glass has excellent insulating properties and high temperature resistance, but it’s brittle, difficult to apply uniformly around conductors, and expensive, so it’s not a practical choice for most standard cables today.

Wood, on the other hand, is not suitable as cable insulation. It absorbs moisture, has unpredictable dielectric properties, can swell and crack, and is flammable. It cannot be reliably used to wrap around a conductor for electrical insulation, especially under varying temperatures and environments.

Therefore, wood is the least commonly used insulation material for electrical cables today.