For the transmission line shielding calculation of SESShield, the user must choose between three classes of transmission line structure so that the program can calculate surge impedance.

None of these classes looks quite like a monopole or a wood pole downlead. However, Class 3 will actually provide you with the exact surge impedance of a cylindrical metallic pole or downlead, despite the illustration of a lattice structure, which is in reality approximated by a cylinder. The value of "2r" shown in the illustration represents the diameter of the metallic cylinder (or downlead conductor) and the value of "h" its height.