Magnet Wire Encyclopaedia

  • Technical terms in the world of enamelled copper wires. Here you can find the explanations.

    Overcoat wire

    Double coated magnet wire. Double coat consists of two separate enamel layers. Most popular overcoat wire has a basecoat made of polyesterimide and a topcoat of polyamideimide (our type SH Therm 210).


    Main cause for blistering in magnet wire surfaces are trapped solvents or moisture (e.g. water from cooling section during annealing process). Once the outer varnish coat is cured such trapped solvents or moisture start vapourising when reaching the hot sections in the furnace. Consequently blistering occurs.

    Elongation on Break

    Unit of measurement for the softness (ductility) of materials, indicates the grade of re-crystallisation in copper. Important for the properties during processing of magnet wires. It decisively determines the form stability of windings. To be influenced by temperature and speed during annealing and in the varnish furnace. Evaluated by extending a magnet wire of defined length to the breaking point. The ratio of elongation on break to original length is the “elongation on break” in percent. Depending on the dimension, the elongation on break for quality magnet wires is between 25 % (0.20 mm) and 45 % (4.1 mm). Working (e.g. pulling) reduces the elongation on break. The elongation on break for hard copper is < 1 %. TENSILE STRENGTH Unit of measurement for materials for resistance to tension. Indicates the power needed totear a test object of defined dimension, and related to the initial dimension of the object. Thetensile strength of hard copper is approx. 450 - 480 N/mm², soft copper 200 -270 N/mm².

    Wire enamels

    Synthetic resin dissolved in organic solvents forming smooth and non-porous coat with good electrical and mechanical properties on conductor after annealing. Share of synthetic resin 20- 45%.

    DSC analysis

    Differential Scanning Calometrics This measuring system is among thermo analysis and takes advantage of the fact that substances consume or release heat during conversion. For DSC tests two seats containing samples are placed and heated in two different furnaces. One seat contains the sample to be tested, the other seat contains a reference sample (usually it is empty). During conversion of the sample object the temperature difference between the two seats is taken as a control signal for the continuous adjustment of the heat output (scanning operation) until it reaches constant zero. The electrical power needed to compensate such differences in temperature is measured and taken down. DSC is used to evaluate the annealing grade of magnet wires, similar to tan-delta tests.

    Dielectric Strength

    Stability of insulation materials. When adding a constantly rising electrical voltage to an insulating material between two electrodes, the electrical field leads sooner or later to destruction of the insulation. The dielectric strength of magnet wires depends mainly on thickness and centricity of enamel coat, surface quality of blank wires and varnish coating, as well as on the annealing grade of enamel insulation. Testing is carried out either by Twisted Pair or wire sampling over cylinders.

    Inclusions in copper

    Contaminants in magnet wires influencing the drawing and enamelling properties negatively, are often caused by preliminary technology processes. Often these inclusions are of ceramic or oxides arising during melting, steel or tinder during rolling process, or even contamination during drawing process.

    Solid body contents

    Percentage of synthetic resin in enamel. Enamels with 40 % solid body consists of 40 % synthetic resin and 60 % solvents. Common solid body contents are between 20 % (thin wires) and 45 % (thick wires).

    Slip additives

    To allow processability of magnet wires on winding machines, a thin coat of lubricant is applied after varnishing process. Common lubricants are diluted paraffin or beeswax (0.5 to 1.0 % dilution in benzine) or soaked in a thread. The amount applied is just a whiff, approximately 40 mg of paraffin on 1 km magnet wire of 0.50 mm diameter that means approx. 22 mg on 1 kg of such wire. Latest inventions in chemistry are about integrating slip additives in the impregnant.

    Grade 1, Grade 2, Grade 3

    Grading of enamel coat thickness of magnet wires by specifying minimum increase of enamel coat insulation as well as the maximum value of the outer diameter of magnet wires. Grade 1 wires have the thinnest enamel coat, grade 3 wires the thickest. Grade 2 begins at the max. limit of grade 1, grade 3 at the max. limit of grade 2. Grade 2 wires are particularly suitable for applications where high reliability is required (e.g. wind power) or to avoid partial discharge in frequency converter-fed motors.

    Perspiration water

    Low molecular parts of solid body in wire enamel are carried along upon vapourisation of solvents and settle as water on the colder parts of enamel equipment (wire cooler, oven entrance, pen). Surface defects occur if the magnet wire touches the perspiration water.

    Cones principle

    The Cones principle relies on several draw-discs with different diameters arranged on an axle to attain different or rising wire speeds.


    Short form Cu (lat. Cuprum), specific weight 8.93 g/ cm³, electrical conductivity 58.5 m/ mm², estimated deposit within the earth's crust approx. 50 kg in 1000 tons. On account of its good electrical conductivity (almost like silver) it is the common conductor in the electrical engineering. Annual consumption of wires approx. 10 million tons world-wide, Cu total consumption approx. 16 million tons, part recycling approx. 40 %.

    Magnet wire standard

    Required characteristics of various magnet wires and determination of required test standards, developed by the IEC (International Electrotechnical Commission), and confirmed by CENELEC (European committee for electrotechnical standards). The requirements are laid down in DIN EN 60317 series, test methods in series DIN EN 60851. DIN stands for “Deutsche Industrie Normung” (German Industrial Standard) and EN for “Europanorm” (European Standard), which are harmonized versions of the former national standards in Europe.

    Bonding of enamel coat

    Bonding strength of enamel coat to the bare copper wire. Tests are carried out on a wire helix and with so-called break tests. The wire helix is wound around a mandrel to reach outer expansions of up to 60 %. Afterwards the wire helix and/ or breaking points are examined under a microscope to investigate the bare length of wire (without enamel coat) taken from the breaking point. Extremely bad bonding strength results in peeling off or detached enamel coat.


    Unit of measurement for the capacity of electrical conductors to conduct current. Reciprocal value of the specific resistance. Cu has an electrical conductivity of 58.5 m/ mm²; that means: A copper wire of 58.5 m length with 1 mm² cross section (~ 1.12 mm ) has a resistance of 1Ω .

    Self-bonding wire

    Enamelled wire with additional coat of thermosetting varnish. This coat bonds by adding heat or solvent. Wires within a winding are attached to each other without extra impregnation. Often this bonding feature is an extra benefit during mounting. Our type SH Bond WD 210 wire is such an overcoat wire, SH Therm 210 with extra coat of thermosetting varnish.


    Disturbing and periodically repeated marks on the wire surface caused by vibration of the wire during drawing process. Such marks are usually caused by incorrect drawing parameters like increased number of loops on the discs, too much slip (discontinuing drawing), or insufficient lubrication. “Crow's-feet” are one-sided chattermarks caused by bad lubrication (e.g. wires runs over an edge). “Corrugated” wires are wires with very strong chattermarks.

    Spring-back angle

    To measure the softness of wire. With a special testing equipment a wire is wound around a mandrel under tension and defined conditions. Afterwards the wires is released and the angle of spring-back is measured.


    Indicates the force needed to leave a lasting deformation that means the material's transition from elastic state to plastic state. The yield point of soft copper is between 120 - 160 N/mm² and depends on the dimension. TEMPERATURE INDEX (TI) Evaluation of life span on samples, the so-called magnet wire twists with an increased dielectric strength evaluation at increased temperatures. Notes concerning the permitted highest endurance temperature TI 200 say that the magnet wire has to have a certain dielectric strength acc. to standard, depending on the dimension and varnish thickness, after 20,000 h at 200°C. LOW-TEMPERATURE BRITTLENESS Occurring of hairline cracks within the enamel coat, if the coating has not been cured sufficiently (oven too „cold“); varnish coat has only been dried, not cross-linked; cold-cracking wire cannot be used; one of the most dangerous defects in magnet wires, however, to be detected in the course of rupturing tests. STYRENE RESISTANCE Modern impregnants (e.g. unsaturated polyester resins) contain styrene as solvents; styrene has the unpleasant feature to create so-called hairline cracks (styrene cracks) in pre-extended wires, with enamel coatings under mechanical tension; the styrene resistance of wires is controlled by sight checks of helix of wires dipped in styrene.

    Tangens Delta

    Dielectric loss factor. Only ideal insulations have no ohmic drops. Insulations like enamels have a minor, but yet verifiable dielectric loss (similar to capacitors), mainly the so-called dipole friction loss. Impressing an alternating voltage on an enamel coat, the dipoles of the molecular structure start vibrating and experience resistance causing friction and heat. Such friction losses are dependent on the chemical composition and significantly on the annealing of the enamel. There is special equipment for testing the dielectric losses depending on temperature. It takes a certain temperature to loosen the molecular structure permitting a strong increase in dipole movement. This increased movements result in a significant rise of the loss factor (tan delta point of inflexion). The stronger the grade of annealing, the higher the point of inflexion. It makes the tan delta test a good indicator for the annealing grade of enamel insulations. The features of magnet wires strongly depend on the grade of annealing, and therefore such tests allow conclusions on the performance of a magnet wire.

    Impregnation of windings

    Coils (in motors, transformers, etc.) are often impregnated with varnishes and resins to increase their operational life span. Commonly such impregnation is made by dip or trickle process. Impregnation has the following purpose: 1.Mechanical protection by hardening and curing of the components of a winding, in particular of magnet wire windings among themselves and each other or with other insulations; 2. Protection against corrosion by preventing humidity, dust, dirt, or any chemical substance to break into the winding; 3. Thermal protection by improving temperature derivation. The heat developing in the conductor is derivated to the sheet package and/ or the environment. Dip impregnation Objects to be impregnated are dipped into the impregnant. Often vacuum is applied to avoid trapped air. After dipping the impregnant is dried and cured in through-type furnaces. This type of process is commonly used for larger windings. Modern technologies are using current-UV-processes, i.e. the windings are heated by means of current before dipping to obtain better absorption of impregnants. And also after dipping process the impregnant is cured by heat developing from current impressed on the objects. UV light supports the curing of outer and therefore colder parts. Trickle impregnation During trickle process the pre-heated and rotating winding is trickled from above with resin (mostly unsaturated polyester resins). By capillary attraction the resin is “aspirated” into the winding. After impregnation the resin is cured by impressing current on the winding conductors. Modern processes support the current curing process by UV irradiation. Trickle processing is commonly used with smaller windings.


    To transmit the power from the discs during drawing process, the wire is placed and wound around the discs several times. When a wire is superposed to another a so-called bypass happens. Such a bypass causes mechanical damages and is often the reason for ruptures. Possible causes are too many enlacements, too much slip, bad lubrication with emulsion, or worn discs.


    Toughness of a substance, resistance of a substance against deformation. The tougher a substance is, the higher the viscosity. Important feature of wire enamels. Evaluated with the so-called viscometer. A viscometer measures the time needed for a certain amount of liquid to leak out through a standardized opening (DIN Cup: 100 ml cup with 4 mm opening). Wire enamels for dimensions between 0.50 and 1.25 mm usually have leakage times of approx. 120 seconds. Thinner dimensions have lower leakage times, thicker dimensions higher leakage times.


    vdx is the product of coating speed in m/ min and magnet wire nominal diameter in mm. Power factor of coating machines. The higher vxd, the more effective the machine. Example: Coating speed 120 m/ min, diameter 0.5, power factor vxd = 120 x 0.50 = 60. The vxd of a machine is almost independent from diameters. vxd allows to calculate the coating speed for any dimension. In our example the coating speed for a diameter of 0.30 mm would be vxd/ d= 60/ 0.30 = 200 m/ min.

    Thermal pressure

    Thermal pressure, also called softening temperature, is an indication for the thermal stability under stress. It is the temperature at which two intersecting, loaded magnet wire test objects are being short-circuited under constant heating and electrical voltage (intersection point softens under pressure and temperature). Outer expansion The proportional expansion of the outermost fibres of the varnish coating on the helix of wire is called outer expansion. It is calculated with the following formula: AFD=d1/(d1+d2)*100 d1 = magnet wire diameter d2 = mandrel diameter Example: D2=d1 (1xd mandrel)AFD = ½ * 100 = 50%

    Heat shock

    To test the adhesion of the enamel coat to the copper under thermal load. A helix of wire (made by winding the wire to be tested around a mandrel) is stored in a thermostatic chamber at increased temperatures for a certain standard period. Afterwards it is checked for cracks under the microscope.

Connection Cables Encyclopaedia

  • Technical terms in the world of litz wires and connection cables. Here you can find the explanations.

    Fire load

    Fire load is the quantity of energy which can be set free through combustion. The fire load of cables is calculated from the heat value and the quantity of inflammable materials used. This value forms a baseline for choosing the security measures to be applied (e.g. the measurement of sprinkler systems and the layout of cable trays).

    Flame retardant (self-extinguishing)

    Flame retardant cables are cables which, when installed as a single cable, although ignitable on exposure to flame source, will greatly reduce flame spread and self¬extinguish once the flame source is removed. However, in a vertical cable bundle, e.g. in vertical risers, fire can spread along the cables (chimney effect). In order to avoid this danger, the so called “non-flame propagating” cable should be used.

    Toxic gases

    During combustion small amounts of toxic gases such as CO and CO2 are inevitably emitted. Combustion gases may not contain any halogen hydrogen compounds (HCl, HF, HBr) nor any strong toxic gases (Phosgene, HCN). The same applies to sulphur and nitric oxides. The toxicity of gases is defined by the so called mortality rate L50. The most relevant internation standards hereto are: NES 02-713 Part 3 (Naval Engineering Standard). The sum of all toxic elements in a material based on a mortality rate L50 after 30 min. impact. Rating by means of dimensionless index number (the lower the better)., and French Standard NF C20¬454, burning of a material sample, no biological damage after 30 min.

    Halogen free

    The halogens are the elements of the 7th group in the Periodic Table of Elements: Chlorine (Cl), fluorine (F), bromine (Br), and iodine (I). Halogen free cables are free of all these elements. They are called halogens because in reaction with bases they build salts (hals: Greek for salt). Chlorine reacts with sodium and builds table salt (NaCl). The halogens are an integrated component of many acids: HCl = Salt acid (hydrochloric acid) HF = Hydrogenfluorid HBr = Hydrongenbromid The most popular plastic containing halogens is PVC (polyvinylchloride). In case of fire or at high temperatures PVC starts to degradate. Hydrochloric acid and other fission products are generated and lead to extremely aggressive corrosion. Therefore the current trend is to replace the halogen containing plastics with halogen free ones. For instance PVC is currently being replaced at a large scale with polyolefin i.e. polyethylene. Thanks to halogen free cables the formation of corrosive and toxic gases can be prevented.

    Circuit integrity

    The circuit integrity indicates how long a non-protected cable maintains its insulation properties, when exposed to fire under certain predefined conditions, without causing a short circuit (as per IEC 60331). A cable is laid horizontally over a burner and kept fro three hours at approx. 800 °C. No short circuit may occur during this time. The circuit integrity is designated with FE (e.g. FE 180 = circuit integrity of 180 min.).

    Corrosive gases

    Corrosive active gases link with humidity and generate aggressive acids which attack metal parts, thus causing great subsequent damages, even if initial fire damage was small. These damages also do not regard directly the area affected by the event of fire. Most endangered are the electric contacts, electronic devices and apparatus, machines, and metal constructions. Even the iron of the concrete reinforcement could be attacked by these acids.

    Smoke density

    The formation of smoke has several unpleasant consequences. On the one hand it considerably lowers the visibility in a fire event, thus impeding the people trapped inside closed room to escape of and the efforts of the firemen to carry on their rescue and fire fighting actions. On the other hand it produces smoke poisoning because of the carbon monoxide. Regarding the formation of the combustion gases the PVC comes off quite badly.

    Limiting Oxygen Index LOI

    According to ISO 4589 the LOI represents the minimum oxygen concentration expressed in percentage of volume which in combination with azote (nitrogen) could still sustain the burning of plastic. LOI 23 = combustible LOI 24-28 = limited flame retardancy LOI 29-35 = flame retardant LOI > 36 = especially flame retardant LOI approx. 45 = peak value at halogen free materials

    Temperature index as per IEC 60216/ VDE 0304 part 21

    The temperature index describes the long-term performance of plastics. The temperature index defines the ageing temperature (in °C), at which the material still has an absolute elongation at break of 50 % after 20,000 hours. A rise in the temperature index of +10 °C results in approximately doubling the life expectation of the plastic. In order to determine the long-term temperature stability of an insulation material the different ageing times corresponding to different temperature are measured and recorded in a so called Arrhenius-Diagram (ordinate-axis: log time, abscissa-axis: the reciprocal absolute temperature). A straight line is drawn to connect the various recorded points. By prolonging the straight line until it intersects the 20,000 hours axis it is possible to determine the lifetime or the temperature index.

    Thermoplastic insulation materials

    Thermoplastics consist of string-like macromolecules which can exist in either an unorganised structure (amorphous) or in an organized structure (crystalline). The transition temperature e of the amorphous phase (tg = brittle temperature) limits its use in cold conditions, the transition temperature of the crystalline phase (Tm = melting temperature) limits its use in warm conditions. Above the melting temperature the crystalline phase disappears, the string-like molecules can move freely and the material begins to flow. The polymer can be processed thermoplastically.

    Infusible (VDE 0472 part 615)

    Electron beam cross-linking enable heat-resistant cables and leads to keep their mechanical properties and remain infusible, even at high temperature (> 100 °C). Cross-linked materials do not drip and therefore guarantee a high operating safety and short-circuit security.

    Cross-linked insulating materials

    Cross-linking binds together the filiform molecules by means of a chemical linking (in the amorphous phase). This leads to a three-dimensional network. The filiform molecules can no longer move freely (irrespective of temperature). Above the melting temperature the material can no longer flow but it goes into a rubber-like elastic state. Advantages of cross-linked insulation materials: -increased shear and compressive strength -improved integrity in case of electrical failures (overload, short circuit) -improved resistance to chemicals -infusible, soldering iron resistance -improved impact strength and crack resistance -better weather- and abrasion resistance


SYNFLEX is a registered Trademark of Synflex
Mylar® is a registered Trademark of DuPont Teijin Films U.S., Ltd. Partnership