Note 1 to entry: The inhomogeneous field condition of a point-plane electrode configuration is the worst case with regard to voltage withstand capability and is referred to as case A in IEC 60664-1. It is represented by a point electrode having a 30 μm radius and a plane of 1 m × 1 m.

Note 2 to entry: For frequencies exceeding 30 kHz, the field is considered to be inhomogeneous when the radius of curvature of the conductive parts is less than 20 % of the clearance.