For transmission of power across long distances, high voltage transmission is employed. Transmission higher than 132 kV poses the problem of corona discharge, which causes significant power loss and interference with communication circuits. To reduce this corona effect, it is preferable to use more than one conductor per phase, or bundled conductors. In addition to reducing corona, audible and radio noise (and associated electrical losses), bundled conductors also increase the amount of current that can be carried compared to a single conductor of equal aluminum content due to the skin effect (for AC lines).