Overvoltage Category, Equipment Class and Pollution Degree: Insulation Design of AC EV Chargers

When buyers compare AC EV chargers, they usually ask about power, connector type and smart features. Certification engineers are watching something less visible: insulation coordination. Under GB 39752 and China’s CCC testing, overvoltage category, equipment class and pollution degree decide clearances, creepage distances, impulse withstand and grounding design before a single prototype passes the lab.

Fixed wall-mounted and pedestal AC chargers are typically treated as OVC III for the unit, while the vehicle connector side sits at OVC II. Incoming mains circuits may be assessed toward OVC IV. Set these wrong and the PCB layout, surge protection and enclosure seals all have to be reworked.

Most fixed AC stations are Class I equipment. They rely on basic insulation plus a reliable protective earth; grounding continuity, insulation resistance and dielectric strength are routine CCC checkpoints. Class II structures use double or reinforced insulation and do not depend on site earthing, but they require a different mechanical and insulation package.

Pollution degree sets the outdoor baseline. Indoor units often start at PD2, while outdoor conductive supply equipment is generally PD3 because dust, moisture and condensation erode surface insulation. That is why IP rating, sealed joints and creepage paths matter as much as the rated current.

The practical rule for manufacturers: OVC defines how big the surge hit can be, equipment class defines the shock-protection path, and pollution degree defines how harsh the micro-environment is. Treat them as one linked design table, not three separate labels.

Certification teams are increasingly rejecting chargers that look finished but lack traceable PE connections, correct terminal isolation and pollution-rated creepage. In 2026, compliance is less about adding features and more about proving the unit stays safe when weather, grid transients and installation conditions are not ideal.