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NEMA MW 1000 - Magnet Wire

Welcome to the home of NEMA MW 1000, Magnet Wire, a standards publication of the National Electrical Manufacturers Association (NEMA). This site tells you about MW 1000, how to use it, and gives updates on revisions as they are approved and published.

About NEMA MW 1000

MW 1000 is the world's premier standard for general requirements, product specifications and test procedures for the manufacture and packaging of magnet wire. First published in 1965, MW 1000 is a dynamic document that is continually developed and maintained by the NEMA Magnet Wire Section Technical Committee, to ensure that specifications and test procedures reflect evolving magnet wire end user requirements and state-of-the-art magnet wire manufacturing technologies.

MW 1000 is designed to present, in concise and convenient form, all existing NEMA Standards for magnet wire, including standards for round, rectangular, and square film insulated and/or fibrous covered copper and aluminum magnet wire for use in electrical apparatus. MW 1000 contains the definitions, type designations, dimensions, constructions, performance, and test methods for magnet wire generally used in the winding of coils for electrical apparatus.

MW 1000 is approved as an American National Standard through an Accredited Canvass of the American National Standards Institute (ANSI). The Canvass body consists of magnet wire stakeholders including wire and test equipment
 manufacturers, end users, government, testing laboratories and others.

Join the ANSI Canvass for NEMA MW 1000. It's free! Inquire here.

What is magnet wire?

Magnet wire (also known internationally as winding wire) is an insulated electrical conductor, usually copper or aluminum that when wound into a coil and energized, creates a useful electromagnetic field. Without magnet wire, electricity is essentially useless. Around 90% of all electrical energy requires modification using magnet wire to be of any use.

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NEMA MW 1000-2018 highlights​

The following is a summary of changes from MW 1000-2016 that appear in the 2018 edition:

Part 1 - General

- Addition of defintions of terms "rounded corner", "rounded edge" and "varnish"

- Addition of basis for defining the Thermal Class of electrical insulating varnishes

- Revision of Tables 4 through 7, dimensional requirements for glass fiber and polyester glass fiber covered wire, to adopt the IEC mathematical progression for calculating overall diameter.

Part 2 - Specifications

- Revision to Dielectric Breakdown at Rated Temperature requirements in specifications MW 18-A, 18-C, 20-C, 36-A, 36-C, 38-C and 84-C to test actual rectangular wire rather than represntative round wire specimens;

- Revision to Thermoplastic Flow requirements in specifications MW 18-C, 20-C, 36-C and 84-C;

- New specifications MW 54-C and 55-C and accompanying title changes to MW 45-C and 46-C, to offer end users separate specifications for varnished and unvarnished polyester glass fiber covered wires;

- Revisions to MW 86 and MW 87 series for consistency with the MW 15 and 18 series

Part 3 - Test Methods

- Revision to 3.9 Continuity, to recognize the use of conductive fiber brushes other than graphite;

- Revision to 3.50 Thermoplastic Flow, to add a new procedure for testing rectangular wire specimens;

- Revision to 3.54 Transformer Oil Resistance and Hydrolytic Stability, to clarify the specimen preparation procedures for the Short-Term Exposure test;

- Addition to 3.57 Bond, to restore the previously published Room Temperature Bond Strength Test Procedure in;

- Revision to Table 34 and 35, expanding the wire size range to 14-37 AWG for testing Dielectric Breakdown properties using the Cylinder Method;

- Revision to Figure 3-8-6, Test Apparatus for Cylinder Method, to correct the ullustration of the test circuitry,


- Addition of Annex I, Repeated Scrape Resistance (informative only)

Coming next: MW 1000-2020! The following are items to be pubished in the 2020 edition, or are under development for the 2020 or future edition:

To be published:

Part 1 - General

- Revisions to Table 3, Dimensions for Self-Bonding Wire to expand the wire size range to include 8-13.5 AWG, providing the magnet wire industry a set of standard dimensional film and bond coat increases encompassing the entire range of self-bonding wire sizes that industry currently manufactures;

- Revision of requirements in clause for the characteristics of aluminum conductors;

- Correction to clause, Application of Insulation, to indicate that insulation tape coverings, not fibrous coverings, shall be wrapped firmly, closely, evenly, and continuously around the wire.

Part 2 - Specifications

- Revisions to specifications for Polyvinyl Acetal film insulated wire to harmonize the Heat Shock requirements for consistency;

- Revisions to MW 102-A and MW 102-C to align their Dielectric Breakdown, Springback and Continuity requirements with the MW 35 series, which is the base specification for “Polyester (amide)(imide) Overcoated with Polyamideimide” constructions;

- New MW 88-C specification for polyvinyl acetal film insulated rectangular aluminum wire with self-bonding overcoat, with accompanying amendments to include minimum dimensional increases due to the bonding layer, and a lap shear bond strength test;

Part 3 - Test Methods

- Revision to the circumferential cut method for determining Adherence and Flexiblity properties, to include photos of a typical fixture and specimen preparation;


- Revisions to Appendix H for Fully Insulated Wire, to align with amendments to IEC 60851-5;

In development:

Part 2 - Specifications

- New specification for MW 16-A Polyimide (Thermal Class to be determined), with requirements to eventually be added for satellite applications,

- Revisions to MW 33-A and MW 33-C specifications for paper tape covered rectangular magnet wire to better align with their counterpart round wire specifications.

- Development of new specification for Polyester Overcoated with Polyamideimide with Self-Bonding Overcoat;

- Development of new specification for Polyamideimide with Self-Bonding Overcoat;

Part 3 - Test Methods

- Investigation into adopting a refrigerant and refrigerant oil compatibility test procedure, to replace the R-22 Refrigerant Extraction test;

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NEMA members that manufacture magnet wire

For 2020, the following magnet wire manufacturers are NEMA members:

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NEMA Contacts

Mike Leibowitz
Program Manager
(703) 841-3264

Kirk Anderson
Industry Manager
(703) 841-3211

Mark Kohorst
Government Relations
(703) 841-3249

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How to Use MW 1000

In the Table of Contents, the Part 2 specifications are first listed in order according to MW specification number, then by Thermal Class for easy reference to a particular type of magnet wire.

To properly use MW 1000, first, review Part 1 for general information, then locate the specification in Part 2 for the particular type of insulation and conductor of interest. Part 2 is arranged in MW number order as shown beginning on page ii. The dimensions for each Part 2 MW type are provided in Part 1 beginning with Table 1. The specification in Part 2 will indicate the performance requirements to be met and references the test procedures and corresponding test values to be attained in Part 3.

Part 1 deals with general information common to all types of magnet wire found in Part 2, including reference documents, definitions, general material requirements, manufacturing information, test conditions and parameters, thermal class information and ordering information. Part 1 also includes dimensions in both AWG and equivalent metric sizes (in mm) for bare wire, minimum insulation increase, and overall dimensions for all MW specifications in Part 2.

Part 2 has all of the NEMA specifications for the particular types of magnet wire listed in the Table of Contents, identified and ordered by “MW” number. The MW number is followed by a “-C” or “-A” to identify the conductor type, copper or aluminum. These specifications provide all of the performance requirements for magnet wire for various types of coatings and/or coverings. Insofar as possible, the product specifications are complete on one sheet since they are arranged to include only one insulation or covering per sheet. The title identifies the product, for example, MW 15-C, Polyvinyl Acetal Round Copper Magnet Wire, while MW 15-A covers the aluminum version of the same generic product.

Part 3 contains the test procedures to be followed and the corresponding tables of specific test values to be attained in determining compliance with the requirements given in Part 2. The requirements are consolidated with the test procedures and testing parameters for a given property. The Table of Contents provides a useful index of the main test paragraphs, beginning on page viii.

Appendix A provides a cross-reference between MW 1000 test procedures and those published by the American Society for Testing and Materials (ASTM International) and the International Electrotechnical Commission (IEC).

Appendix B provides definitions, requirements, and recommended test procedures for reusable magnet wire packaging, standardized dimensions for spools and reels, and standard formatting for the labeling of magnet wire products.

Appendix C provides a cross-reference of MW specifications with those published by the IEC.

Appendix D provides the formulas used for determining dimensional requirements, minimum dielectric breakdown voltage, and cross-sectional areas and conductor resistance

Appendix E defines the dimensional criteria for ranges of sizes of rectangular bare, film insulated, and fibrous covered magnet wire. These tables provide the general rules and guidelines for various rectangular magnet wire products that are not standard as defined in Part 1. For convenience, cross-references to the corresponding tables in Part 1 are provided.

Appendix F provides important information on selected refrigerants that could be used as alternatives to monochlorodifluoromethane (refrigerant R-22), including chemical compositions, boiling points, critical pressures and critical temperatures.

Appendix G provides industry recommended winding tensions for de-reeling of magnet wire onto end user winding equipment.

Appendix H defines the requirements and test procedures for zero-defect fully insulated magnet wire (FIW).

Appendix I provides a recommended method for repeated scrape resistance, commonly specified by magnet wire end users.

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Comparison to international standards

NEMA specifications and test methods differ from those published by the IEC. The following is a general summary of these differences:

Dimensions: NEMA dimensional requirements apply American Wire Gauge (AWG) wire sizing, while dimensional requirements in IEC standards apply metric sizing in mm. Therefore the requirements are not exactly the same, but some overlap occurs between the standards. The IEC and NEMA methods for determining dimensions are technically equivalent.

Resistance to Refrigerants: Both the NEMA and IEC procedures specify the use of monochlorodifluoromethane (refrigerant R22). Since R22 is no longer permitted in new equipment, investigation is ongoing for identifying suitable alternative refrigerants commonly used in newer refrigeration equipment, to test magnet wire for hermetic applications. The challenge in transitioning to alternative refrigerants is establishing which refrigerants lead to meaningful test results.

Available Specifications: Annex C of NEMA MW 1000 cross-references NEMA and IEC magnet wire specifications. Not all NEMA specifications have a corresponding IEC specification number and vice versa.

Solderability Requirements: NEMA immersion time requirements for larger wires are more stringent than those specified in IEC specifications. The IEC and NEMA methods for determining the solderability of a given wire construction are technically equivalent and both standards recognize the use of lead-free solder alloys upon supplier/customer agreement.

Continuity Requirements: The NEMA continuity requirements for single build (Grade 1) wire more closely reflect the capabilities of present day manufacturing equipment than do IEC requirements. However, closer harmony between NEMA and IEC requirements for heavy and triple build (Grade 2 and 3) constructions was achieved upon publication of IEC 60317-0-1:2013, and in the present maintenance work program for IEC 60317-0-1, the requirements for Grade 2 and Grade 3 are proposed to be fully harmonized.

Test Procedures: There is an ongoing effort to harmonize IEC and NEMA test procedures. The following summarizes notable differences in these procedures:

Heat Shock: Differences exist between the test specimen preparation procedures, namely the degree of pre-elongation of wire specimens and the diameter of the test mandrels used for wrapping wire specimens. The NEMA-specified total elongation of wire specimens (pre-stretch + mandrel wrapping) is more stringent than IEC, which specifies only a mandrel wrap.

IEC TC 55 decided not to specify pre-stretching that would result in total elongations equivalent to those in MW 1000.

Dielectric Breakdown: MW 1000 has adopted a shot electrode methodology for determining breakdown of rectangular and large round wires, based on IEC 60851-5. Both MW 1000 and IEC 60851-5 recognize the cylinder method for round enameled wires. MW 1000 is being revised to specify the cylinder method for the same wire size range as that of IEC 60851-5.

Thermoplastic Flow (Cut Through): IEC 60851-6 specifies a single-point method of evaluation. This could be adopted in MW 1000 in the future as a routine test, however for now MW 1000 recognizes a rising-point method as a qualification test.

Bond Strength: The IEC and NEMA helical bond peel test procedures are essentially equivalent.

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End user information

The following information can be downloaded free of charge:


Download and listen to the following:

Companion NEMA publications:

  • ANSI/MW 1000-2015 Supplement
  • MW 750, Dynamic Coefficient of Friction of Film Insulated Magnet Wire

    to be revised in 2020 to include static C of F test

  • MW 765, Reclaiming of Magnet Wire Packaging
  • MW 785, Simulated Insertion Force Test for Film Insulated Magnet Wire

    to be revised in 2020

  • MW 820, Conductor Softness Test Methods
  • Under development: Authorized Engineering Information document for pulse endurance test

  • Under development: Authorized Engineering Information document for accelerated thermal aging of magnet wire insulation

  • NEMA IPDP 1-2018, Magnet Wire Insulation Removal methods

IEC Test Method standards:


  • Click h​ere if you have any questions about this page, NEMA or magnet wire standards.
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