ELF magnetic fields from nonarmoured multi-core power cables

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 distance decays at a rate greater 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 >0.2 m. Other issues concerning the installation of power cables in buildings are also discussed