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Copper Magnet Wire

Specialty Wire

Bare Wire Products

Packaging Information

Magnet Wire Questions

Litz Wire Questions

Aluminum and Other Metal Questions


Do you carry copper rod or tubing?

Troubleshooting Questions

Buying from Us Questions

Environmental & Toxic Substance Regulation Questions

My company requires product content declarations to respond to toxic hazard surveys from our customers.  How can I get this information for the products purchased from MWS Wire?

Magnet Wire 

Q: What is magnet wire?
A: It is an insulated copper or aluminum conductor typically used to wind electromagnetic devices such as motors and transformers. The insulation may be a thin film of varnish called enamel; a fibrous polyester or fiberglass yarn; or a combination of both enamel and fibrous insulations.  The fibrous insulation may be impregnated with a varnish to bind the insulation to the conductor and enhance thermal endurance.  Other conductors such as copper and nickel alloys, pure nickel, precious metal plated copper and pure precious metals can also be coated with film insulation for custom applications.

Q: What is winding wire?
A: It is another name for magnet wire.

Q: What does AWG stand for?
A: “American Wire Gauge” is the standard used to represent successive diameters of wire. The system is based on the establishment of two arbitrary sizes: 0000 (4/0 or ‘4-aught’) defined as exactly .4600” diameter and 36, defined as exactly .0050” diameter. The ratio of these two sizes is 92 and the sizes between the two are based on the 39th root of 92, or approximately 1.123, so the nominal diameter of each gauge size increases approximately by this factor between AWG 36 and AWG 4/0 and decreases by this factor   between AWG 36 and AWG 56, which is the smallest practical diameter for commercial magnet wire. Nominal wire diameters to AWG 44 are rounded to the fourth decimal place and aren’t necessarily rounded to the nearest digit.  A chart of nominal AWG gauge sizes is on page 31 of the MWS technical data booklet which can be accessed on our website.

Q: What is insulation build?
A: Build is the measurement of insulation obtained by subtracting the bare wire diameter from the overall (insulated) diameter. Build is equal to two insulation wall thicknesses measured 180º apart on the circumference of the wire.  For acceptance purposes, the measurement for insulation build is the average of three measurements made at 120º intervals around the wire circumference. There are four different builds: single, heavy, triple, and quadruple. Insulation build is directly correlated to dielectric strength. 

Q: How many types of magnet wire insulations are there?
A: There are a number of film insulation types ranging from temperature Class 105 to Class 240.  Each film type has its own unique set of characteristics to suit specific needs of the user. Please refer to ‘Insulated Products’ on the left side menu bar on our website for more information about the insulation types available.

Q: How do I calculate the amperage for a given round magnet wire?
A: The formula for current carrying capacity in amperes for copper magnet wire wound into a coil is: d2 x 4869.48 (d = diameter in inches). This formula is pretty conservative, and formulas from other sources based on straight lengths of solid or stranded conductors in ambient air may indicate greater current carrying capacity than this one.

Q: Can you just send me the standard magnet wire?
A: MWS stocks a variety of wires with insulation types ranging from Class 105 to Class 240.  There are also a variety of sizes, conductors, and insulation builds to consider. A very common wire used in many applications is single build polyurethane Class 155 with a nylon topcoat (SPN). It is stocked in most sizes and is a good general-purpose insulation for people that don’t know exactly what they want.  Armored polyester (APT) insulation is another option when a higher temperature class is desired.

Q: How do I figure out the feet per pound conversion of a given gauge size?
A: A Ft/Lb conversion table can be easily downloaded from this website under the “Technical Data Booklet” heading.  

Q: Is the wire I buy from MWS RoHS Compliant?
A: The overwhelming majority of wire products produced and supplied by MWS Wire Industries are in compliance with Directive 2002/95/EC of the European Parliament. We will continue to supply solder plated wire containing lead and cadmium plated and cadmium copper alloy wire to our customers that want and need these products. All products sold exceeding RoHS threshold levels of lead or cadmium carry a RoHS non-compliance statement on the packing slip, certification and invoice so any MWS customer can determine if they have purchased a product containing lead or cadmium above the threshold level.

Q: Why would someone want to use square shaped wire instead of regular round wire?
A: Square wire is useful where space constraints are concerned. When formed into a coil an equivalent amount of square wire put in a coil can be placed in a tighter coil configuration than the same amount of round wire. 


Q: Why are many magnet wires given a topcoat of nylon (polyamide)?
A: The mechanical properties of nylon are advantageous due to its lubricity and low coefficient of friction. It makes magnet wire more durable and easier for machines and people to handle without damaging the conductor or primary insulation coating. However, nylon is hygroscopic, meaning it can absorb moisture from the surrounding environment, which can lower the dielectric strength of the film insulation.

Q: What is the advantage of using bondable wire?
A: Bondable wire has a thermoplastic adhesive film superimposed over standard film insulation. When activated by heat or solvent the bond coating cements the winding turn-to-turn to create a self-supporting coil. The use of bondable wire can eliminate the need for bobbins, tape or varnishes.

Q: What type of lubricant goes onto the wire surface?
A: A lubricant is applied to film coated magnet wire to ensure compact winding and ease of de-reeling for the user. Lubricants commonly used are very dilute solutions of paraffin wax or mineral oil in a volatile solvent. Isoparaffinic fluids have also been used in certain applications. Without the application of lubricant the winding on the spool may be ‘spongy’ or become tangled and difficult to de-reel. However, special orders can be manufactured without lube on request.

Q: What is the shelf-life of magnet wire?
A: Magnet wire shelf life is not established in commercial specifications. As long as the wire has been carefully stored it may be usable for years to come. Bondable wire should not be stored at temperatures exceeding 100°F.

Q: What is the purity of the copper that goes into magnet wire?
A: Electrolytic tough pitch copper (ETP Copper, UNS C11000) exceeds 99.9% purity and is the most widely used type for magnet wire production.  It is intentionally oxygenated (200-400 ppm) to achieve the best combination of conductivity, capacity for being cold worked and economy. MWS can also supply wire made from high purity (99.95%) OFHC Copper (UNS C10200) or Certified (99.99%) OFHC Copper (UNS C10100).

Q: What are the out-gassing properties of nylon serve in litz wire and insulation?
A: Information provided by DuPont many years ago informed us that the melting temperature of nylon is 258°C, but no decomposition products will result from melting. At 160-170°C nylon will oxidize and change crystalline structure to where absorbed moisture will be driven off. Thermal degradation of the polymer begins between 350-400°C with ammonia, carbon monoxide and oxides of nitrogen out-gassing.

Q: How should we store the magnet wire we bought from MWS?
A: The enamel on the magnet wire surface is very stable in ambient environments. Storage in any dry, room temperature environment will ensure the best shelf life.  Bare copper and silver items react to oxygen and other trace elements in the air. To slow surface oxidation on bare or plated items they are packaged in anti-tarnish wrappers and plastic bags.

Q: Can the wire MWS sells be used in conjunction with ultrasonic bonding processes?
A: MWS has supplied magnet wire to customers using ultrasonic bonding processes. That being said, ultrasonic bonding requires insulation stripping and bonding techniques that must be developed by the user.

Q: My drawings call for Formvar magnet wire. Can I get that in a small gauge size?
A: MWS stocks Formvar insulated magnet wire in most sizes to AWG 51.  Across the industry the use of solderable films such as Class 155 polyurethane-nylon have supplanted Class 105 Formvar.  Formvar remains superior to poly-nylon in properties such as abrasion and chemical resistance, and stability at very low temperatures.  Thus, it continues to be used in oil filled transformers and certain cryogenic applications.

Q: Do you sell Plain Enamel in most gauge sizes?
A: MWS inventories Plain Enamel (PE) magnet wire in AWG 42 and 43 only but other sizes may be custom produced.

Q: Do you sell wire made and wound without lube?
A: Yes, call our sales department for more info.

Q: How is the temperature class for magnet wire insulation determined?
A: Samples of insulated wire are made into twisted pairs and aged at a series of temperatures significantly higher than the expected temperature class rating of the insulation.  The twisted pairs are periodically proof tested at 300 to 1200 volts depending on the wire diameter.  Sample failures are recorded and an average life at each temperature is calculated in accordance with procedures established in ASTM D2307.  From these values a regression line is calculated to determine the temperature at 20,000 hours of aging.  This temperature must be equal to or greater than the proposed temperature class for the insulation.


Litz Wire

Q: What is the difference between MWS TwistiteTM and Litz Wire?
A: Both are twisted multi-conductor products that find use in RF applications but otherwise the two are substantially different.  While litz wire may be produced with 15 or fewer individual strands, for high frequency applications the constructions often consist of many bundles with up to 2000 individual strands of ultrafine wire.  Litz wire is constructed with a loose lay (<0.25 to 2 twists per inch) to minimize the lineal increase in resistance produced by twisting and individual wires are insulated with single build insulation to maximize the cross sectional area of copper conductor.  Polyurethane base insulation is used almost exclusively for the individual wires due to its low RF loss characteristic, wide availability and moderate cost.  The constructions of fine and ultrafine strands may be helically wrapped with nylon or other textile yarn to bind and maintain the litz wire in a circular configuration and to protect the thin film insulation coatings from abrasion.  In recent years extruded coatings such as FEP have been used in place of a textile serve.  Twistite™  Magnet Wire is usually fabricated from just two to ten individual strands that are twisted much tighter, up to 50 twists per inch.  Twistite™ products may be constructed from any film insulation type from Class 105 to Class 240 and individual strands may be coated to heavy, triple or quad builds to suit the application. Twistite™ strands are often individually color coded for easy identification whereas this feature is not a concern in litz constructions.

Q: When talking about litz wire, what does “serve” mean?
A: Serve is a textile yarn insulation helically wrapped around litz wire.  Litz wire can be made with or without a serve. The insulating yarn is usually nylon but Celanese™, cotton and even silk can be utilized to serve litz wire.

Aluminum and Other Metals

Q: I know that copper is a better conductor than aluminum.  How much lower is aluminum’s electrical conductivity?
A: The conductivity of electrical conductor grade aluminum wire (Alloy 1350-0) is 61.8% of the equivalent cross-sectional area of annealed ETP copper.  Therefore aluminum wire must have 1.6 times the cross sectional area for a given copper wire in order to achieve a comparable DC resistance.

Q: What are some other advantages and disadvantages of using aluminum over copper?
A: Aluminum is lighter and less costly per pound than copper. However, the disadvantages include electrochemical decomposition, lower fatigue strength, and the buildup of a hard sapphire oxide coating. In addition, resistivity is higher at 16.782 ohms/cmf compared with 10.371 for copper.

Q: I need Beryllium Copper but also need RoHS approval.
A: At this time beryllium is not on the list of materials restricted by the European Union. However, beryllium is a listed toxic substance in other regulations and therefore there are some safety concerns for handling this alloy. As a solid in finished parts such as wire, beryllium copper presents no particular health hazard. However, breathing beryllium dust from machining or welding may cause serious lung damage. 



Q: Do you carry copper rod or tubing?
A: No – we specialize in copper wire with an accent on fine sizes.



Q: I want to use a magnet wire insulated with polyimide in an application that gets hotter than 240oC.  Will that be a problem?
A: Polyimide insulated magnet wire is rated to operate continuously at 240oC (see ‘How is the temperature class for magnet wire determined?’).  However, the magnet wire may handle temporary spikes in temperature up to 400oC.  Keep in mind that excursions above the rated temperature can shorten the life of any electrical component.

Q: We wash all our polyimide insulated magnet wire in water, and keep having problems.  Do polyimide and water mix?
A: Care should be taken not to entrap moisture. If you do wash the wire, make sure it is completely dry before using in production. Water at room temperature will probably not cause problems.  However, tests show degradation occurs in polyimides under a synergistic combination of moisture, heat, and mechanical strain. 

Q: I’m having trouble de-reeling the wire.
A: Proper equipment is essential for de-reeling wire.  Fine wire, flat wire and ribbon present additional challenges because the former is easily stretched when de-reeled at high speed as in a coil winding process, and the latter products easily tangle or twist if constant, sufficient back tension is not maintained on the wire spool.

There are two basic techniques for de-reeling round wire. In the first the spool is in a fixed, stationary position where the wire is pulled over one flange and routed through guides and devices to control back tension.  A disc fitted with thin plastic filaments at its circumference (‘wisker disk’) can be placed on the spool flange to pre-tension the wire as it passes the spool flange, or a rotating ‘flyer’ device can be used to guide the wire as it is pulled off the spool. The stationary spool method is unsuitable for flat wire and ribbon because they can permanently twist when de-reeled in this way.  In the second technique, the spool rotates on a shaft or other support mechanism and braking force must be carefully applied to provide consistent back tension without stretching the wire.

There are a number of de-reeling device manufacturers for a wide range of wire gauges.  Some we know of are: 


Azonic Products

Filmtec, Inc.

Itasca Engineering

Magnetic Technologies

Wyrepak Industries

Buying from Us

Q: Can I pay with a credit card?
A: Yes.

Q: I am having problems getting my email through to a salesperson.  What is wrong?
A: First, check to make sure you have the right email...all of our email addresses end with “mwswire.com” (note: a common mistake is putting “mswwire” or “mswire”).  If that is not the problem your message may be inadvertently trapped in the spam filter.  Please call us and we will ensure your emails will get to their proper destination. 

Environmental & Toxic Substance Regulation Questions

Q: Is MWS registered to ISO 14001, the environmental management system standard?
A: No, however MWS has a decades-long record of comprehensive, conscientious environmental regulatory compliance and has taken proactive steps to reduce waste, manage environmental impacts and conserve raw materials and energy.  The latest is a facility-wide project upgrading interior lighting to energy efficient T8 lamps and electronic ballasts controlled by occupancy sensors.  In 2007 MWS installed a 155 kW photovoltaic solar electric generating system that supplies nearly 50% of the company’s energy needs while transmitting power back to the grid on weekends and holidays when the business is closed.  MWS is also a past winner in the Waste Reduction Awards Program sponsored by the California Integrated Waste Management Board.  [see more information at http://www.mwswire.com/news.htm].

Q: Are products sold by MWS RoHS compliant?
A:The great majority are but we also inventory solder plated and cadmium plated wire, and cadmium copper alloy wire for our customers who need these products.  Complete information regarding product compliance with the RoHS directive is available at http://www.mwswire.com/rohs.htm

Q: Does MWS have analytical data establishing RoHS compliance for magnet wire products?
A: Yes.  Copper conductor, film insulations and dyes have been analyzed for cadmium, lead, hexavalent chromium, mercury, polybrominated biphenyls (PBB) and polybrominated diphenyl ethers (PBDE).  For a copy of the data which can be printed or downloaded use this link: http://www.mwswire.com/rohs_analytical.htm

Q: Has MWS pre-registered or registered the substances and preparations used in its products to comply with the European Community’s REACH [Registration, Evaluation, Authorization and restriction of CHemicals] legislation?
A: No.  As a non-Community entity, MWS is not permitted to directly register substances and has not contracted with a third party ‘only representative’ to do so.  However, magnet wire and other wire types supplied by MWS meet the REACH definition of an article, do not intentionally release substances during normal and foreseeable conditions of use, and do not contain substances of very high concern (SVHC) on the candidate list.  Our current REACH fact sheet may be accessed at http://www.mwswire.com/pdf_files/reach.pdf

Q: My company requires product content declarations to respond to toxic hazard surveys from our customers.  How can I get this information for the products purchased from MWS Wire?
A: Send your request by e-mail to ken@mwswire.com or call us at (818) 991-8553.

NEMA Connect

Headquartered in Westlake Village, California USA, MWS inventories more than 50,000
Magnet and Specialty wires along with production facilities for drawing, shaping, serving,
twisting and insulating of wire for high-technology users worldwide.

Established in 1968