Proximity effect means the interaction of magnetic fields associated with adjacent current carrying conductors parallel to each other causing a further redistribution of the current which likewise increases the ohmic d.c. the resistance of the conductor. Proximity effect increases with the conductor diameter and becomes maximum when the cables are practically in contact. Therefore, a correction is mainly necessary for L.T. cables of large cross section. Again this effect can also become important under the certain condition of cable installation. When cables are laid parallel to metal beams, walls etc as frequently happens in buildings or ships this effect increases the apparent impedance of these cables appreciably. Ultimately proximity effect exerts influence on the current carrying capacity of the cables.
A horizontal spacing is desirable in order to reduce the effect of mutual heating. In case they close or touch one another the effect of mutual heating increases and accordingly, the current carrying capacity of cable decreases sufficiently.