Extremely low frequency (ELF) magnetic fields from large current-carrying conductors are causing concern in high rise office buildings because of the potential to cause interference with sensitive equipment. ELF fields produced by multi-core power distribution cables are discussed. A theoretical model for calculating the magnetic field produced by such cables is presented, which is validated by experiment. It is found that the magnitude of the field with distance decays at a rate greater than exponentially, and that the phase angle of the field changes spatially. Based on the model, simplified formulas are derived which can fully characterise the magnetic field produced by a multi-core power cable. The ELF fields predicted by the formulas are validated by measurements, and are found to be highly accurate at distances > 0.2m. Other issues concerning the installation of power cables in buildings are also discussed.
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