What Is Creepage Distance and Why Does It Matter?

Creepage distance is the shortest path along an insulating surface between two conductive parts. It is a different concept from "clearance" (the shortest straight-line distance through air), and it directly affects safe operation in polluted and humid environments.

Creepage distance vs clearance

• Creepage distance: the shortest path along the insulating surface.
• Clearance: the shortest path through air.
• Both determine insulation performance, but creepage distance focuses on surface flashover.

What is specific creepage

Specific creepage is the ratio of creepage distance to system line voltage (or phase voltage), in mm/kV. It measures "how much surface insulation distance is needed per unit voltage", allowing comparison across voltage classes.

Pollution classes and recommended specific creepage

• Class I (light): about 16 mm/kV.
• Class II (medium): about 20 mm/kV.
• Class III (heavy): about 25 mm/kV.
• Class IV (very heavy): about 31 mm/kV.

Why it matters

In coastal, chemical, sandy or foggy areas, the insulating surface accumulates contamination and moisture, forming a conductive path that can flash over under overvoltage. Adequate creepage distance is the fundamental defence against pollution flashover.

How to increase creepage distance

• Increase the number and diameter of sheds.
• Use deep or alternating shed profiles.
• Use composite silicone sheds (better hydrophobicity).

Always determine specific creepage from the actual pollution conditions of the site rather than blindly applying the minimum. Ever Power provides porcelain bushing solutions with creepage distance matched to IEC 60815 pollution classes.