Diagram of two adjacent wires carrying an alternating (AC) electric current (I, red arrows) in opposite directions, showing the origin of proximity effect. Proximity effect is a redistribution of current in a AC current-carrying conductor, due to currents induced by the time varying magnetic field of an adjacent conductor from Faraday's law of induction. In parallel wires carrying current in opposite directions, as here, it causes the current to concentrate on the side of the conductor adjacent to the neighboring conductor. It is caused by the magnetic field (B, green arrows) of the adjacent wire. The drawing shows the currents and magnetic field at a point in the AC cycle when the current is increasing. The time varying magnetic field from the lefthand wire passes through the righthand wire, creating circular eddy currents (E) in the wire. During the part of the AC cycle when the current is increasing the eddy currents circle in a counterclockwise direction as shown. The eddy current adds to the main current on the left side of the wire (1) increasing the current density there, and subtracts from the main current on the right side of the wire (2) reducing the current density there. The resulting current density profile is shown by the red arrows, and color gradient on the cross section of the wire (3), with blue indicating lower current density, and green, yellow, and red progressively greater current density. During the other half of the cycle while the current is decreasing, the eddy currents are in a clockwise direction, reversing the current.