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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 wiretakeholders 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 members that manufacture magnet wire

For 2014, the following magnet wire manufacturers are NEMA members:

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NEMA Contacts

Mike Leibowitz
Program Manager
(703) 841-3264

John Marcario
Industry Manager
(703) 841-3266

Jonathan Stewart
Government Relations
(703) 841-3245

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How to Use Your Hard Copy of 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).

Appendix B consists of 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 International Electrotechnical Commission (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 an alternative to R-22, including their 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.

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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 use monochloro-difluoromethane (refrigerant R22). Since R22 is no longer permitted in new equipment, an investigation is underway to identify suitable alternative refrigerants commonly used in newer refrigeration equipment, to test magnet wire for hermetic applications. The challenge is establishing which refrigerants lead to meaningful test results.

Available Specifications: Appendix 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 when a new edition of IEC 60317-0-1 was published in 2013.

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.

Thermoplastic Flow (Cut Through): IEC 60851-6 test methods for thermal properties has 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.

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End user information

The following information can be downloaded:


Download and listen to the following on your mp3 player:

Companion NEMA publications:

  • MW 750, Dynamic Coefficient of Friction of Film Insulated Magnet Wire
  • MW 765, Reclaiming of Magnet Wire Packaging
  • MW 785, Simulated Insertion Force Test for Film Insulated Magnet Wire

IEC Test Method standards:

Revisions to NEMA MW 1000-2014:

Amendments to the 2014 edition are in process and will appear in a new 2015 edition. Check back for this summary in the first quarter of 2015


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