Proximity Effect

Proximity Effect is a phenomenon which is observed in conductors carrying alternating current. When a conductor carries ac power, the constantly varying magnetic field induces eddy currents in the nearby conductors. In conductors where the current flows in the same direction, this results in increased current density in the nearby conductors due to the changes in the current distribution across the cross-section of the conductor. Thus the resistance of the conductor increases.

In the picture, the blue zone inducts the areas with high current density, the white zone indicates low current density caused by mutual induction.

When two conductors carrying current in the same direction are located close by, the current density on the sides of the conductor adjacent to each other will be lesser than the sides on the outside.

The reduces the net current carrying capacity of the conductor. This phenomenon is not observed when dc current flows through the conductor as there is no induction in dc.

Thus the AC resistance of a conductor may be many times the DC resistance. The AC resistance is directly proportional to the frequency of the power supply. The proximity effect is an important factor considered during the design of transformers, motors and multi-core cables.

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