Proximity Effect

Proximity Effect refers to the phenomenon where the resistance of one conductor in a transmission line or a bus bar decreases due to the magnetizing flux from another conductor in close proximity.  

When two conductors are placed close to each other the varying magnetic flux caused by one conductor induces currents in the other conductor.  This increases the current density in the other conductor and results in increased impedance. 

The Proximity Effect increases with frequency.  Conductors are usually spaced with a sufficient distance to minimize the Proximity effect.