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 approved as an American National Standard through the NEMA MW 1000 Consensus Body accredited by the American National Standards Institute (ANSI). The Consensus Body consists of magnet wire stakeholders including wire manufacturers, end users, and other general interest parties.

Join the NEMA MW 1000 Consensus Body. 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 Highlights

ANSI/NEMA MW 1000-2023

The following is a summary of changes from MW 1000-2020 that appear in the 2023 edition:

Part 1—General

  • Revision to the scope of to advise that the standard does not address quality assurance procedures or any other aspects of quality assurance

Part 2—Specifications

  • Modification to the titles and insulation descriptions of all specifications in MW 1000, Part 2 for polyester-based film insulated magnet wire
  • Designation of certain magnet wire specifications as obsolete

Part 3—Test Methods

  • Revisions to the Refrigerant Extraction and Dielectric Breakdown After Refrigerant Conditioning procedures to:
    • reflect the phase-out of R-22 refrigerant
    • reflect the use of replacement refrigerants, with a calculation to determine the quantity of refrigerant placed in the pressure vessel
    • recognize the use of alternative rinsing solvents to methylene chloride, and
    • discuss the presence and effects of refrigerant oil, referencing one example method for determining compatibility between wire enamel, refrigerant and refrigerant oil.
  • Revisions to Table 36 for Dielectric Breakdown of rectangular and square magnet wire

Annexes

  • Revisions to Annex C cross-reference of NEMA and IEC specifications to reflect the current standardization activity of both organizations

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    NEMA Members that Manufacture Magnet Wire

    For 2024, the following magnet wire manufacturers are NEMA Members:

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    NEMA Contacts

    Danny Abbate
    Technical Director – Industrial Sector
    (703) 841-3256

    Mike Leibowitz
    Technical Fellow – Industrial Sector
    (703) 841-3264

    Marta Yuste Prieto
    Director, Regulatory and Industry Affairs – Industrial Sector
    (703) 841-3204

    Todd Sims
    Director, Regulatory and Industry Affairs – Building Codes
    (703) 841-3221

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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.

    Annex 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).

    Annex 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.

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

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

    Annex 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.

    Annex 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.

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

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

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

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    Comparison to International Standards

    MW 1000 is a complete volume containing all general requirements, specifications and test methods for magnet wire in a single document for convenience. IEC specifications and test methods on the other hand, are each published in separate documents. NEMA specifications and test methods differ from those published by the International Electrotechnical Commission (IEC). The following is a general summary of these differences:

    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.

    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.

    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.

    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.

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

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

    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 has been revised to specify the cylinder method for the same wire size range as that of IEC 60851-5.

    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.

    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. A new consideration is that refrigerant oils used in today’s compressors can be more aggressive on wire insulation than refrigerants. IEC 60335-2-34 contains a test for determining wire insulation compatibility with refrigerant and refrigerant oils.

    Solubility: The MW 1000 Solubility procedure differs from IEC in that MW 1000 requires the wire to be immersed in xylene or other specified liquid, then needle-scraped using the specified test equipment, whereas in the IEC procedure, the wire specimen is scraped via pencil with specified hardness. In both methods, the conductor is then electrically tested to determine if there is any exposure of the bare conductor.

    Thermal Endurance: The method for determining the thermal classification of magnet wire is essentially the same between IEC and NEMA Standards. The Standards used IEC 60172 and ASTM D2307, respectively outline a multi-temperature thermal cycling aging test procedure with a dielectric diagnostic test after each cycle on round wire test samples. The IEC 60172 Standard also includes a method for evaluating rectangular wire test samples.

    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.

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    End User Information

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