Horizontal & Vertical Sphere Gap The sphere gap can be used for Impulse, AC and DC voltage calibration according to the IEC 60052 recommendation. The spheres are arranged vertically or horizontally, one being mobile. In the vertical version the mobile sphere is remotely adjusted using an electrical drive. I the horizontal version, both spheres are mounted on columns of insulation material hence enabling to superimpose impulse AC and DC voltages. It is also possible to use the gap in a peaking circuit. For the chopping of lightning impulses the sphere gap can be equipped with the optional chopping device.