Litz wires are power cables that are made up of several individually insulated wires. This type of wire is designed specifically for use with alternating current (AC) power in order to reduce the undesired effects of two different phenomena. These phenomena, which are known as the proximity and skin effects, can both result in a decrease of efficiency in higher frequency AC power. The way that a litz wire deals with the skin effect is by providing a smaller cross section profile in each individual wire. Since each component wire can also be twisted, it is also possible to minimize the proximity effect.
One of the main issues with the use of high frequency alternating current is a phenomenon known as the skin effect. In the case of very high alternating current frequencies, this effect results in most of the electricity being conducted near the surface of a wire instead of evenly distributed throughout. The portion of the wire that actually carries the current is known as a skin-depth. Since the bulk of the wire is unused for current transfer, this is a wasteful situation that can also result in a reduction of efficiency. One way to deal with the skin effect phenomenon is to hollow out the wire so that the unused portion is no longer there, but the litz wire can be a more compact solution.
In order to deal with the skin effect, each litz wire is made up of many smaller wires. Each of these wires has a diameter that is about one skin-depth wide so that all of the material can be used to conduct electricity. The individual wires can be bundled together, and in some cases several bundles will then be turned into a single wire. Higher frequencies require thinner individual wires, so it can be important to know the characteristics of the alternating current in a particular application in order to choose the correct litz wire.
Another issue that the litz wire can deal with is the proximity effect. This is a phenomenon that results in an overall higher resistance when multiple wires are carrying electricity in close proximity to one another. The current can be constrained to a smaller area than normal, resulting in a situation known as current crowding. In order to deal with this issue, each component wire can be twisted. Many different types of insulators can be used, though polyurethane is often chosen because it does not need to be removed before soldering the wire.