Frequently Asked Questions

It is another name for magnet wire.

“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.

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.

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.

The formula for current carrying capacity in amperes for copper magnet wire wound into a coil is: Diameter Squared 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.

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.

A Ft/Lb conversion table can be easily downloaded from this website under the “Technical Data Booklet” heading.

The overwhelming majority of wire products produced and supplied by MWS Wire Industries are in compliance with Directive 2011/65/EV and 2015/863 amending Annex II of the European Parliament. We will continue to supply solder plated wire containing lead to our customers that want and need these products. All products sold exceeding RoHS threshold levels of lead 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 above the threshold level.

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.

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.

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.

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.

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.

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).

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.

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.

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.

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.

MWS inventories Plain Enamel (PE) magnet wire in AWG 42 and 43 only but other sizes may be custom produced.

Yes, please call our sales department for more info.

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.