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. MW 1000 is also endorsed by Electro-Federation Canada (
EFC) for use in Canada and by La Asociación de Normalización y Certificación del Sector Eléctrico (Association of Standardization and Certification of the Electrical Sector (
ANCE) for use in Mexico.
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 2013, the following magnet wire manufacturers are NEMA members:
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NEMA Contacts
Mike Leibowitz
Program Manager
(703) 841-3264
John Miller
Industry Manager
(703) 841-3202
Sarah Owen
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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Get your copy of the current ANSI/NEMA MW 1000 today!
MW 1000-2011 (Revision of MW 1000-2008) is available through IHS/Global Engineering Documents. Click here to order.
Approved Amendments
The following Revision 3 amendments to MW 1000-2008 (designated MW 1000-2011) were approved as an American National Standard effective February 14, 2012:
Clause 1.3, Definition of build: to editorially delete the formulas that define each insulation build and refer to these same formulas already in Appendix D, Table D.1
Clause 1.5.2.1: to define the size ranges of intermediate round wires where formulas for dimensional increases apply, while max OD’s for sizes finer than 46 AWG would be agreed upon between customer and supplier.
Clause 1.5.2.4: to refer to the Appendix D formulas for determining Dielectric Breakdown
New note to Tables 1-1 and 1-3: to indicate that for Table 1-1, Single and Heavy Build 47-56 AWG, and for Table 1-3, Type 1 (47-52 AWG) and Type 2 (47-50 AWG), values are based on manufacturing capabilities at the time of publication.
Amended Table 1-1 note ‡: to indicate that nominal bare wire diameter is published for reference only and to reference Table 1-2 for required resistance measurements determined according to 1.6.7.2.
Amended Clause 1.6.7.2 Ultra Fine Dimensions: for consistency with the proposed amended note ‡ in Tables 1-1 and 1-3.
Revision to clause 1.6.8, Periodic Conformance: to define "periodic conformance" tests more precisely and to reflect current industry practice
New definitions: for the terms "number of tapes" and "number of layers" to bring consistency in terminology relevant to paper covered magnet wire throughout the standard.
New Tables 1-25, 1-26 and 1-27: to standardize dimensions for paper and tape covered magnet wire. The relevant specifications in Part 2 have been amended accordingly.
Introductory page to Part 2: to specify that testing protocol and requirements of magnet wire products that fall outside the AWG size ranges indicated in DIMENSIONS given in the Part 2 specifications shall be as agreed between the user and supplier.
Amendment to MW 31-C: to specify the wire size range to which dimensional requirements apply.
Determination of dimensions of rectangular wire: to provide a method more practical for the manufacturing environment and to reduce scrap.
Table 3.3.1, Adherence and Flexibility and Heat Shock specimen preparation: to correct errors for calculating total elongation using a 5d mandrel, and to define "Total Elongation"
New Clause 3.3.7, Adherence and Flexibility: to replace the Coverage test with test methods for paper wrapped magnet wire, but specific to round sizes 4/0 - 9 AWG and rectangular wire.
Revision to Solderability test: to specify a specimen immersion depth with a tighter tolerance, and to note regarding lateral movement of the immersed wire specimen in order to minimize dross remaining on the surface of the soldered portion.
Appendices: to designate each as either normative or informative, to clarify their intent as either requirements or information only.
New Appendix G: to publish non-normative industry recommended winding tensions.
The following Revision 2 amendments to MW 1000-2008 were approved as an American National Standard effective September 30, 2010:
Definition of "Degree of Overlap"
Rationale: to add clarity to the standard, in that the term is not explained in the specifications or general requirements. Also, the standard lacks any illustration of its application. The new definition also standardizes on terminology associated with the manufacture of tape and paper covered magnet wire, preventing the use of non-standard terms such as "wrap" and "percentage of overlap".
Revised Solderability requirements for MW 28C, 82-C and 83-C
Rationale: to adopt the IEC based multiplier approach to solder bath immersion times.
Addition of half-AWG sizes to Part 3 tables
Rationale: assigns test requirements in certain Part 3 tables that lacked half-AWG wire sizes
Note in Table 1-1 and 1-3 on Quad Build magnet wire
Rationale: to indicate that the minimum film insulation increases and maximum overall diameters in the table do not apply to MW 16-C Quad. Requirements for MW 16-C Quad appear in Table Q (MW 16-C).
Addition of Half-AWG wire sizes to Table 1-3, Self-bonding magnet wire
Rationale: to encourage the use of published half-AWG requirements for self-bonding wire in place of customized end user requirements. The half-AWG bare wire and minimum increases due to the film coating adopt those published in Table 1-1. Max OD’s are taken directly from Table 1-1 based on the definitions of Type 1, 2 & 3 self-bonding wires in Clause 1.3. Half-AWG minimum increases due to the self-bond overcoat are determined by adopting the next larger full-integer AWG minimum increase.
MW 2-C, 3-C, 6-C and 17-C to obsolete effective Dec. 31, 2012
Rationale: The wire constructions are no longer manufactured, UL does not recognize them, and they are not specified internationally
Reorganization of clause 1.5.2, Intermediate Sizes
Rationale: Rules that apply to dimensional requirements and test requirements and procedures are reorganized to separately describe the treatment of dimensional and test requirements for users of the standard.
Amendments to "3.55 Refrigerant (R22) Extraction" and "3.56 Dielectric Breakdown After R22 Conditioning" procedures \
Rationale: to alert users of the standard that when considering the use of alternative refrigerants to R-22, their differing properties such as critical pressure and temperature do not allow direct substitution for R-22 in the test procedure. Certain alternative refrigerants can be used in the test, but critical pressure and temperature must be taken into consideration and the refrigerant wire manufacturer should be consulted. A new Appendix F lists these refrigerants and their critical properties.
Clause 3.56, Retained Dielectric Breakdown After R-22 Conditioning, is revised to specify proper disposal of refrigerant after the test is completed.
The following Revision 1 amendments to MW 1000-2008 were approved as an American National Standard effective November 20, 2009:
Clause 1.3, Definitions - addition of the term full rounded edge
Rationale: In the process of developing new standard dimensions for bare insulated rectangular wire in Table 1-8, it was determined that the term full rounded edge should be defined to ensure precision in its application. A drawing is included to make the standard more user friendly.
Clause 1.3, Definitions - addition of terms for "rectangular wire" and "square wire"
Rationale: to provide clarification to users of the standard, the differences between the dimensional tables in Part 1 for rectangular wire and for square wire
Revised Table 1-8, Dimensions, Radii and Cross-Sectional Area for Standard Rectangular Bare Wire
Rationale: to encourage the use of standard dimensions and minimum increases for rectangular wire
Amendment to Part 2 introduction
Rationale: to clarify that the wire size ranges in the DIMENSIONS section of each specification in Part 2 determines the range of wire sizes to be tested to Part 3 test procedures
Reorganization of MW 16-C Polyimide Round Film Insulated Wire, Class 240
Rationale: consolidates the dimensional and performance requirements of the four insulation builds, and to assign revised and unique Dielectric Breakdown and Scrape Resistance requirements for MW 16-C Quad to the appropriate sections of Part 3
Amendments to Table 3.3.1
Rationale: to assign half-AWG wire sizes to align with the addition of half-AWG wire sizing in Table 1-1, and to encompass the entire range of copper and aluminum wire sizes in Part 2 specifications.
Table 3.4.1, Elongation, and related Part 2 specifications
Rationale: to accurately and consistently reflect the Part 2 elongation requirements for all rectangular wires having a thickness of <0.049 in. from 32% to 30%, and correspondingly, to replace these Part 2 elongation requirements with a reference to Table 3.4.1.
Clause 3.5, Heat Shock
Rationale: to clarify that the procedure applies to both round and rectangular wire
Clause 3.9.2, High Voltage Continuity
Rationale: to specify calibration of test equipment based on fault resistance and to provide specifications on carbon brush electrodes to be used as part of the test apparatus
Clause 3.13, Solderability
Rationale: to note the availability of alternative lead-free solder alloys, which are agreed upon between customer and supplier
Clause 3.54, Transformer Oil Resistance and Hydrolytic Stability
Rationale: to permit testing of a range of wire sizes, not just 18 AWG, to provide guidance on the number, length and/or weight of specimens, and to specify the materials to be used for the test.
Clause 3.57, Bond
Rationale: to reorganize the procedures to make it clear as to how the test is to be conducted in each possible condition. In addition, specifications for self-bonding wire in Part 2 are modified editorially for clearer reference to the appropriate type of test procedure.
Part 3, Tables of test requirements
Rationale: to assign half-AWG wire sizes to clarify and document the appropriate break where a different test method is used.
New Appendix E
Rationale: to relocate the dimensions from former Tables 1-13 through 1-18 into a new informative reference section. These dimensions are considered to be non-standard relative to the amended Table 1-8.
Specifications MW 47-C and MW 48-C
Rationale: to require MW 47-C wire to have a silicone varnish, the same tracer requirements as in MW 48-C, and Springback requirements up to 4 AWG, not 4/0 AWG. Both MW 47-C and MW 48-C should adopt the MW 43-C and 44-C requirements for treatment with a modified silicone insulating varnish or silicone compound for a tough outer finish. All changes are editorial in nature because they restore the requirements that were published in MW 1000-1997.
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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.
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.
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. There will be closer harmony between NEMA and IEC requirements for heavy and triple build (Grade 2 and 3) constructions later 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 has decided not to specify pre-stretching in order to obtain total elongations equivalent to those in NEMA MW 1000.
Dielectric Breakdown (for rectangular wire): 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:
Companion NEMA publications:
- MW 750-2009, 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
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