EMP Shielding Properties of Conduit Systems and Related Hardware
CONSTRUCTION ENGINEERING RESEARCH LAB (ARMY) CHAMPAIGN IL
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This report presents the results obtained by CERL over the past 3 years under its investigation of the shielding properties on conduit systems, conduit-related hardware, and the effects of improper field assembly on the shielding of conduit systems. The measurements were made by injecting EMP-type current pulses onto test conduits and measuring the signal picked up on a sense wire inside the conduit. Results are presented for the measurement of both diffusion and leakage signals. The diffusion signal provides a base line for the conduit shielding since it is the optimum shielding obtainable for a given size and material of conduit. The leakage signals represent a degradation of the conduit shielding due to the insertion of conduit hardware required to assemble the conduit runs, or to the improper assembly of the conduit system. Included in the leakage study were various hardware items including couplings, unions, conduits of various sizes, flexible conduit, condulets, lock nuts, threaded hubs, and a variety of condulet gaskets. In addition, the effects of thread corrosion, use of different conductive compounds, various methods of compound application, welding near couplings, and the inadequate tightening of threaded joints were evaluated. The greatest single factor in the degradation of the shielding effectiveness of conduit assemblies was the inadequate tightening of conduit joints.
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