Protection of cables by grounding structures

Conduits of various shapes offer good electromagnetic protection to cables placed inside. As measure of protection, the transfer impedance has been studied; in the frequency range of interest the current adjusts between the low and high frequency distribution in the conduit. Quasistatic two-dimensional calculations are based on the method of moments and on conformal transformations. Practical U, H, L and T shapes are studied mostly. Engineering equations directly give the dominant parts of the transfer impedance for various cable positions inside non-magnetic conduits. Measurements on U conduits confirmed the models.