Experimental measurements of ELF magnetic fields from cable trunking

In buildings rectangular enclosures (e.g., metallic trunking) are often installed to provide mechanical protection for distribution conductors. This paper presents the results of an experimental investigation into shielding of galvanized iron trunking. First, characteristics of galvanized iron trunking are presented against its design parameters. It is found that the non-linear material property of galvanized iron has a significant effect on magnetic shielding. The actual performance of galvanized iron trunking is affected by several factors, such as, size, thickness, and material, as well as current magnitude and cable spacing. The concept of an equivalent linear shield is introduced to evaluate shielding performance for nonlinear trunking