Electromagnetic coil applications depend on magnet wire as a conductor of electricity. Magnet wire is copper or aluminum wire coated with a thin layer of insulation that is coiled to create an electromagnet. Insulation can be made from a variety of materials, each of which affects the conductivity of the wire.
Magnet wire insulation has two primary purposes. It provides an electrical barrier between conductor turns on a coil and offers heat and moisture resistance for strength and thermal protection.
This guide outlines general conductor properties and provides a breakdown of insulation types and their characteristics.
General Conductor Properties
The properties of conductors affect the current that flows through them; therefore, it’s important to consider these things when choosing conductors:
- Conductance: The amount of current that can pass through a given wire. The resistance of the wire material is how much it resists or opposes the current.
- Inductance: The tendency of a conductor to oppose a change in the current that passes through it. The higher the rate of change, the greater the voltage will be across the inductor.
- Physical properties: These include density, thermal capacity, thermal conductivity, thermal coefficient of expansion, melting point, and tensile strength.
- Area and weight: Both affect resistance. Increased wire length adds resistance; however, wire with a larger cross-section reduces it.
- Electrical: These include IACS volume conductivity, volume resistivity, thermal coefficient of resistance, and change in unit resistance at 20°C.
- Resistance correction: Ambient temperature and thermal insulation can affect electric current, and a material’s resistance usually increases as temperature rises, and must be calculated when selecting a conductor material.
- AWG system: This is the standard for sizing single-strand, round, and solid wires in North America. Sizes range from 0000 AWG 0.460 in. to 44 AWG 0.0022.
- Winding tensions: Winding tension recommendations are outlined in the Essex Handbook and specify maximum and minimum winding tensions for copper and aluminum wire.
Wire Insulation Properties
Insulation properties enhance safety and performance. Key insulation characteristics include:
- Superior insulation resistance: Prevents current leakage
- High dielectric strength: Withstands voltage breakdown
- Effective mechanical strength: Endures excess handling
- Non-flammability: Reduces fire hazards
- Non-hygroscopic properties: Resists exterior moisture infiltration
- Environmental resistance: Resists hazards like acids and alkalis to prevent corrosion and chemical reactions
Magnet Wire Insulation Guide
Sometimes called winding wire, magnet wire is the heart of an electromagnet. Different wire coatings and coverings ensure effective insulation.
Specifications include:
- Thermal Class
- Insulation Type
- NEMA Standards (MW1000)
- Federal Specifications
- Insulation Characteristics
| Thermal Class | Insulation Type | NEMA Standard (MW1000) | Federal Specification (JW1177) | Insulation Characteristics |
|---|---|---|---|---|
| 105C | Plain Enamel | NONE | NONE | Plain Enamel, known as oleoresinous enamel, was one of the first film insulations developed more than 75 years ago and is still in use today in a variety of electronic components. Plain Enamel wires are manufactured to single‐build dimensional standards. Available in 40‐44 AWG. |
| Formvar | MW 15 (RD), MW 18 (SQ/RECT) | JW1177/4 (RD), JW1177/16 (SQ/RECT) | Formvar Enamel is made from vinyl acetal resins produced as a smooth uniform film. Formvar has excellent mechanical properties such as abrasion resistance and flexibility. |
|
| Polyurethane Bondable Formvar Bondable Polyurethane Nylon Bondable | MW 3 MW 19 MW 29 | JW1177/44 JW1177/6 JW1177/30 | Bondable magnet wire is insulated copper wire with a superimposed film of thermoplastic bonding material. The bonding material is activated by heat or a solvent making it possible to wind coils in tight and unusual shapes since the wire may be bonded turn‐to‐turn as it is being wound. | |
| 155C | Polyurethane‐155 | MW 79 | JW1177/41 | Polyurethane‐155 is a 155°C thermal class solder strippable insulation produced primarily 30 AWG and finer with quick soldering characteristics at 390C |
| Polyurethane Nylon‐155 | MW 80 | JW1177/42 | Polyurethane Nylon‐155 is similar to the 155°C Polyurethane with an additional Nylon overcoat to improve the abrasion resistance and heat shock characteristics for coil and motor windings |
|
| 180C | Polyurethane‐180 | MW 82 | NONE | Polyurethane‐180 combines the thermal properties of a class 180°C insulation, while offering low temperature solderability at 390 C. |
| Polyurethane Nylon‐180 | MW 83 | NONE | Polyurethane Nylon‐180 offers excellent abrasion resistance for ferrite core coils and transformers, while exhibiting high temperature thermal stress and low temperature solderability at 430C |
|
| Polyester‐imide | MW 30 | JW1177/12 | Polyester‐imide magnet wire is insulated with a Class H modified polyester resin. It has excellent thermal endurance, solvent resistance and exhibits a low coefficient of friction to improve windability. |
|
| Polyester Nylon | MW 76 | JW1177/38 | Polyester Nylon is a film insulation with a modified polyester basecoat and a nylon topcoat. Typical of a dual coat construction, advantage is taken of the high thermal properties of the polyester and the mechanical properties of the nylon | |
| Solderable Polyester | MW 77 | JW1177/39 | Solderable Polyester magnet wire is an ester‐imide insulated wire which solders at 470°C. |
|
| Solderable Polyester Nylon | MW 78 | JW1177/40 | Solderable Polyester‐Nylon magnet wire is a two‐part insulation system in which ester‐imide basecoat is overcoated with nylon. This wire solders at 455C |
|
| Polyester‐imide Bondable Polyester‐amide‐imide Bondable Solderable Polyester Bondable | NONE NONE NONE | NONE NONE NONE | Self‐bonding polyester actually describes a number of possible constructions of polyester base insulation with a thermoplastic bond coat. The bond coat is heat or solvent activated. |
|
| 200C | Glass Fibers Dacron Glass (DDG) | MW 44 (RD), MW 43 (SQ/RECT) MW 45 (RD), MW 46 (SQ/RECT) | JW1177/21 (RD) JW1177/20 (RD),JW1177/25(SQ/RECT) | Both glass and Dacron glass are a served filament on the magnet wire conductor. They are available as unvarnished or varnished with organic or silicone varnishes. The fibers may be served over bare conductor or over film constructions. The glass is a continuous filament glass yarn and the Dacron glass is a combination of glass and polyester fibers. Glass offers high resistance to overload burnout and Dacron offers excellent abrasion resistance and flexibility. |
| Polyester‐200 | MW 74 | JW1177/43 | Polyester‐200 is a modified theic‐polyesterimide one‐part system. It has high temperature thermal properties and good chemical resistance. |
|
| Polyester‐Amide‐Imide | MW 35 (RD), MW 36 (SQ/RECT) | JW1177/14(RD),JW1177/13(SQ/RECT) | Polyester‐amide‐imide magnet wire is a two‐part insulation consisting of a modified polyester basecoat with a superimposed amide‐imide outer coating. The wire exhibits exceptional windability, heat shock resistance and ability to withstand overloads. Excellent chemical resistance to most solvents and insulating varnishes. | |
| Polytetrafluoroethylene (Teflon) | NONE | NONE | Teflon has high heat resistance and excellent resistance to most solvents, acids and corrosive chemicals and a high dielectric constant. |
|
| 240C | Polyimide‐ML | MW 16 (RD), MW 20 (SQ/RECT) | JW1177/15(RD),JW1177/18(SQ/RECT) | ML is a film insulation made of polyimide resins. It is a Class 240 C thermal rated insulation with exceptional resistance to chemical solvents and burnout. The wire ability to withstand excessive overloads extends the use of the magnet wire in extreme conditions. MS is unaffected by prolonged exposure to varnish solvents. |
NOTE: For reference only. Wire manufacturer specifications may vary.
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