What is the purpose of creepage distance in insulator design?

• A. Provide a long enough surface path to resist surface arcing under polluted and humid conditions.
• B. Shorten the path to improve mechanical strength.
• C. Increase thermal dissipation.
• D. Reduce manufacturing cost.

Answer: (C)

Creepage distance is the length of the conductive path along the surface between two conductors or between a conductor and a ground point. Its purpose is to prevent surface arcing and tracking, especially in polluted and humid conditions where a thin conductive film can form on the insulator surface and reduce surface resistance. If the surface path is too short, the voltage can drive a discharge across the surface, leading to flashover or leakage currents. By designing a longer creepage distance, the surface discharge path is made long enough to withstand the operating voltage without arcing, even when contamination and moisture are present. This is why the correct description is that creepage distance provides a long enough surface path to resist surface arcing under polluted and humid conditions. It’s not about mechanical strength, heat dissipation, or reducing cost.