Creepage, Clearance, and High-Voltage Isolation in PCB Design

Protecting Circuits Against Electrical Arcing

High-voltage power electronics—such as electric vehicle chargers, solar inverters, and power supplies—require physical isolation between high-voltage domains and low-voltage control circuits. Failure to maintain adequate physical separation leads to electrical insulation breakdown, dielectric tracking, and dangerous short circuits.

Compliance with safety standards such as IEC 60664 and UL 840 requires precise calculation of clearance and creepage distances during PCB layout.

Distinguishing Clearance and Creepage

1. Clearance: The shortest distance through air between two conductive elements. Adequate clearance prevents atmospheric electrical arcing during high-voltage surges.
2. Creepage: The shortest path along the surface of the PCB insulation material between two conductors. Creepage prevents dielectric tracking, where surface dust and humidity form a conductive leakage path over time.

Design Techniques for High Isolation

• Board Isolation Slots: Cutting physical milling slots or air gaps into the PCB between high-voltage pads eliminates the surface path, replacing creepage distance with air clearance distance.
• Conformal Coating: Applying protective conformal coating seals the board surface against moisture and dust, allowing reduced creepage spacing under applicable industrial safety standards.