Editing Overhead power line (section)

===Circuits===
A ''single-circuit transmission line'' carries conductors for only one circuit. For a [[Three-phase electric power|three-phase]] system, this implies that each tower supports three conductors.

A ''double-circuit transmission line''  has two circuits. For three-phase systems, each tower supports and insulates six conductors. Single phase AC-power lines as used for [[Railway electrification system|traction current]] have four conductors for two circuits. Usually both circuits operate at the same voltage.

In HVDC systems typically two conductors are carried per line, but in rare cases only one pole of the system is carried on a set of towers.

In some countries like Germany most power lines with voltages above 100 kV are implemented as double, quadruple or in rare cases even hextuple power line as [[rights of way]] are rare. Sometimes all conductors are installed with the erection of the pylons; often some circuits are installed later. A disadvantage of double circuit transmission lines is that maintenance can be difficult, as either work in close proximity of high voltage or switch-off of two circuits is required.  In case of failure, both systems can be affected.

The largest double-circuit transmission line is the [[Kita-Iwaki Powerline]].

<gallery widths="230" heights="230">
File:Single circuit overhead power line with distribution lines.png|A single-circuit 138 kV line (top) with distribution wires (bottom)
File:Electric Sails.jpg|A double-circuit line
File:Img0289SCE 500kV lines close.JPG|Parallel single-circuit lines
File:Hamilton Beach Pylon (2).JPG|Four circuits on one tower line
File:Wernau Double Pylon1.JPG|six circuits of three different types
File:Stromtrasse bei Mannheim-Seckenheim.jpg|Various powerlines (110/220 kV) in Germany with double and quadruple circuits
</gallery>