One of the most important materials in a winding is the magnet wire used for the coils.  The type of enamel or varnish used to coat the copper wire affects several thermal, physical,  and electrical properties.  Achieving  the desired results in a finished winding means using the right type of magnet wire from the start.  Many factors influence the decision of which type of wire can be used in a particular design.  SM Windings uses an array of electrical engineering tools and formulas to determine which type to use in each motor winding.  Some common types of magnet wire are listed in the chart below, however there are dozens more that each possess their own unique characteristics.  

Winding Materials - Magnet wire with enamel coating used in winding manufacture
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Magnet WireCoating/Wire TypeCharacteristics
EAIWAmide-imide over Polyester-imide Enameled WireRated at 200°C continuous.
Resists abrasion, moisture, solvents, and refrigerants
AIWAmide-imide Enameled WireExtra resistant to chemicals and solvents.
Provides extra overload and breakdown protection.
EIWPolyester-imide Enameled WireRated at 180°C continuous.
Good thermal stability, flexibility, and adhesion.
PEW+NYPolyurethane Overcoated Polyester Enameled WireGood thermal stability, excellent abrasion resistance.
Good for high speed winding machinery.
PEWPolyester Enameled WireRated at 155°C continuous. Excellent dielectric properties and thermal stability.
IFDWInverter-Fed Driven Motors WireRated at 200°C continuous.
Protects against transient spikes and high frequencies in harsh electrical conditions.


Insulation is important for thermal properties as well as electrical isolation in a winding.  A dip in resin or varnish is often used to protect the magnet wire from shorting or arcing beyond the capability of the magnet wire’s own enamel. This dip in varnish also gives more rigidity to the winding to help prevent issues with flexing and friction between wires.  NEMA rates motor insulation materials as A, B, F, or H.  SM Windings uses class F and H insulating materials that offer the most protection for the windings and withstand higher temperature ranges without breaking down.  Higher voltage windings may also have slot insulation in the form of polyimide impregnated paper.  This added insulation gives the magnet wire additional protection from arcing and shorting in high voltage winding.


The winding itself is connected to the outside of the motor by the lead wires, typically in a junction box for connecting the motor’s input supply.  Cross linked polyethylene or XLPE insulated leads are chemical and moisture resistant and can be used in high temperature and high voltage applications.  Various chemicals can be added to the insulation of the lead wires to achieve flame rating, resistance to extreme temperatures, or voltage capacities of 1000V+.

Winding Materials - XLPE Cable
Winding Materials - RTD Resistance Temperature Detector
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Other components are sometimes used in the process of producing a winding, especially for protection of the winding. Temperature Switches, Resistance Temperature Detectors (RTD’s), Thermistors, and Thermocouples are all devices that can be used to detect excessive heat in the winding.  Some of these devices can interrupt the power supply to the winding to prevent permanent damage.  Others are used for monitoring and signalling hazardous conditions so that a person can take the appropriate action.  Solutions like embedded RTDs that are actually installed in the stator slots or end turns of a winding give more accurate readings and can help increase the service life of the winding.