Litz wire

Litz wire is used in high-Q inductors for radio transmitters and receivers operating at low frequencies, induction heating equipment, and switching power supplies.

Due to the dual inverse nature of the electromagnetic field, the skin effect dominates at frequencies less than about 2 MHz; at higher frequencies, the proximity effect becomes the dominant force, and Litz wire induces more DC losses than solid wire or tube conductors.

As the frequency rises and the skin depth gets smaller than the wire diameter, skin effect becomes significant, the current is increasingly concentrated near the surface, and the resistance per unit length of the wire increases above its DC value.

In applications where multiple wires carrying the same current lie side-by-side, such as in inductor and transformer windings, the proximity effect causes additional current crowding, resulting in an additional increase in the resistance of the wire with frequency.

One technique to reduce the resistance is to place more of the conductive material near the surface where the current is by replacing the wire with a hollow tube of the same cross-sectional area.

The tank coils of high-power radio transmitters are often made of copper tubing, silver plated on the outside, to reduce resistance.

Each thin conductor is less than a skin-depth, so an individual strand does not suffer an appreciable skin effect loss.

[6] At frequencies above about 1 MHz, the benefits become gradually offset by the effect of parasitic capacitance between the strands.

[8] Litz wire has a higher impedance per unit cross-sectional area, but litz wires can be used at thicker cable sizes, hence reducing or maintaining cable impedance at higher frequencies.

Multiple parallel twisted strands of enameled wires can be found also in transformers in some switching power supplies.

It consists of 9 × 5 × 5 × 27 (totaling 6,075) strands of #36 AWG (0.127 mm [0.0050 in] diameter) magnet wire and multiple layers of cotton, hemp, and plastic insulation, in a cable 19 mm (3⁄4 inch) in diameter, totaling 151,875 circular mils (0.7695619839 cm2) of copper.