Chamfering and edge rounding

Radiusing a busbar edge does three jobs. Electrically, a sharp corner concentrates the field; a radiused edge distributes it more evenly at the same creepage distance, which raises the partial-discharge threshold. Mechanically, insulation — heat-shrink, epoxy encapsulation, polyimide film, overmoulding — conforms to a radius, where a sharp corner leaves air voids at exactly the point of highest field stress and those voids become the breakdown initiation site. Practically, a radiused edge is safe to handle during assembly. Typical radii run from about R2 to R10 depending on bar dimensions, voltage class and environment. Edge radius is specified by the fabricator as an engineering means of meeting the clearance, creepage and dielectric provisions of IEC 61439.