Creepage and clearance

Where mains or other hazardous voltages are present, safety standards such as IEC 62368-1 specify how far apart conductors must be. Clearance is the shortest path through air; creepage is the shortest path along the surface of the insulating material, which matters because dust and moisture can form a conductive track over time. The required distances depend on working voltage, insulation type (basic or reinforced), pollution degree, material group and altitude.

Galvanic isolation (transformers, optocouplers, digital isolators) separates hazardous circuits from anything a user can touch. It is also used on communication links between distant equipment, such as RS-485 between buildings, to break ground loops.

Where it bites: adding creepage late in a dense design often means board slots, a bigger board or different components. Certification labs measure these distances directly.