Enamelled copper wire

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Transformer from 1969. Coil made of CuL.

Enamelled copper wire (CuL) is a copper wire that has been coated with an electrically insulating enamel layer during manufacture . The thickness and weight of this lacquer insulation is very low compared to other insulation materials with the same effect. This wire is therefore preferred for the construction of electrical coils , transformers and machines . Further applications are solderable jumper wires and the production of high-frequency stranded wire .


A roll of enamelled copper wire (wire diameter 0.18 mm)

By using enamelled copper wire, the mechanical size of electrical machines is reduced in a favorable manner, with spatial savings effects resulting from the concentration of the electrical and magnetic fields in a smaller space within the scope of the winding technology . Ultimately, this reduction in size also leads to energy savings with the same power output due to shorter cable routes.

The enamelled wires are classified according to the standards 60317 and 60851 created by the International Electrotechnical Commission (IEC). Wires are classified according to temperature index (long-term use temperature), breakdown voltage and thermal shock behavior.

Wire enamels are solutions of polymers in mostly cresolic solvent mixtures. All wire enamels are coated on special wire enamelling machines and baked at 300–600 ° C. In order to obtain smooth, concentric and pore-free films, enameled wires are usually varnished and baked between 6 and 20 times. As a rule of thumb, the enamel film makes up approx. 10% of the weight of the enamelled copper wire. The resulting increase in diameter is called the increase. The solvents are evaporated and catalytically burned. The heat is used to heat the system. The polymers crosslink and insoluble films are formed. When soldering enamelled copper wire - even already stripped with a blade or sandpaper - small amounts of highly toxic toluene-2,4-diisocyanate can be released. For this reason, an extraction system is required for regular work with enamelled copper wire; for occasional work, the work area should be well ventilated.

Polyurethane enameled wires can be soldered, which means that they can be soldered without removing the enamel beforehand. The soldering process requires temperatures> 340 ° C; at the same time, the polyurethane film decomposes instantly due to the low thermal resistance of the urethane group. Harmful gases are produced.

Lacquered individual wires connected to a twisted conductor with paper insulation for the entire conductor

For winding wires in coils, transformers, relays and motors, coatings with polyesterimides have established themselves as film formers. Depending on the composition and selection of the raw materials, films with different thermal, mechanical and dielectric properties are obtained. Polyesterimides are made from ethylene glycol , THEIC, dimethyl terephthalate , trimellitic anhydride , diaminodiphenylmethane in a polycondensation reaction . Commercially available polyesterimides have a hydroxide mass ratio between 100 and 300 mg / g and a molar mass that is below 5000 g · mol −1 . They are supplied as approx. 40% solutions in a solvent mixture. Polyesterimides are the most frequently used wire enamels in Europe. Polyesterimide enamelled wires are only partially solderable, but only from 450 ° C.

In the case of coils with high layer voltages and / or high frequencies such as transformers in switched-mode power supplies , it is common to soak the windings made with enamelled wire in a vacuum and to dry them in order to avoid pre-discharges in the air gaps and thus the dielectric strength to increase in continuous operation.

Baked enamel wire

Baked enamel wire is used for self-supporting coils that are manufactured without a coil body . Its coating consists of a temperature-resistant basic insulation and a top layer that adheres by heating and often also polymerizes, which bonds the individual turns to one another and thus gives the coil mechanical strength and stability. That is why they can be used specifically for the production of flat and cylinder coils.

For negligence in the processing, electrical breakdown or due to prolonged predischarges in air gaps, however, the enamel insulation can be damaged, it is created to adjacent wire layers a winding short . Due to the current induced in the resulting short-circuit winding, the insulating varnish is further destroyed by the heat, so that the interturn faults spread and the bare wires ultimately form a short circuit .

Enameled copper hollow wire

Enameled copper hollow wire has a continuous cavity in the middle and is one of the hollow wires. During operation, coolant is continuously pumped through the hollow wire via an additional coolant supply, thus dissipating the heat. In this way, the enamelled copper hollow wire can be operated with a higher current density than without cooling and thus allows more compact, smaller and lighter wound goods with the same output. The enamelled copper hollow wire differs from waveguides from the field of generator technology in that it is endlessly manufactured, and its dimensions are on the order of a few millimeters and thus significantly smaller. This means that it can be wound with conventional winding machines.


  • Franz Zach: Power Electronics - A Manual. 5th edition, Springer Verlag, Wiesbaden, 2015 ISBN 978-3-658-04898-3 .

Individual evidence

  1. Thermal product features according to IEC 60317 (PDF; 71 kB).
  2. THEIC (Tris-2-Hydroxyethyl Isocyanurate) -modified polyimides as enamelled wire insulation ( Memento of the original from May 11, 2011 in the Internet Archive ) Info: The archive link was automatically inserted and not yet checked. Please check the original and archive link according to the instructions and then remove this notice. . @1@ 2Template: Webachiv / IABot / www2.dupont.com
  3. from 450 ° C solderable polyesterimide enamelled wire ( Memento of the original from May 31, 2014 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. . @1@ 2Template: Webachiv / IABot / www.pack-feindraehte.de
  4. ^ Baked enamel wire ( Memento from December 18, 2015 in the Internet Archive ).
  5. ^ Franz Zach: Power Electronics - A Handbook . 5th edition. Springer Verlag, Wiesbaden 2015, ISBN 978-3-658-04898-3 , pp. 1832 .
  6. Edmund Nitsche, Michael Naderer: Internally cooled hollow wires, doubling the power density of electric motors . In: ATZelektronik . tape 12 , no. 3 , June 1, 2017, ISSN  1862-1791 , p. 44-49 , doi : 10.1007 / s35658-017-0035-0 ( springer.com [accessed June 28, 2017]).