Creepage/Clearance Estimate

Formula

Description

Creepage and clearance are the minimum distances required between conductors at different potentials to prevent electrical breakdown. Clearance is the shortest distance through air; creepage is the shortest distance along the surface of insulation. This rough estimate (Vpeak/500 mm) provides a starting point for PCB layout, but actual requirements depend on the safety standard (IEC 62368, IEC 60950, UL), pollution degree, altitude, insulation type (basic, supplementary, reinforced), and material group. Always consult the applicable safety standard for the final design.

Variables

• V_peak — Peak working voltage between conductors (V)

Practical Notes

The result is in millimeters (using the forward solver). For 230 V mains (325 Vpeak), the estimate is about 0.65 mm clearance, but IEC 62368-1 typically requires 1.5-2.5 mm depending on conditions. At higher altitudes (above 2000 m), clearance must be increased due to lower air pressure. Creepage depends on the Comparative Tracking Index (CTI) of the PCB material. Standard FR-4 is CTI group IIIb (175-249 V). Slots and grooves in the PCB can increase the effective creepage distance.