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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.
It is another name for magnet wire.
Magnet wire is classified by:
– Size of the conductor (in AWG – American wire guage, or SWG – Standard wire guage, or in mm or inches)
– Thickness of insulation
– Type of enamel and its thermal class
ROHS stands for Restriction of Hazardous Substances and its certification means that these restricted substances are not used in the manufacturing of wire beyond specified limits.
Magnet wire is governed by various standards, but the most often used standards, for both copper and aluminum, in the industry are (IEC) International Electro technical Commission, (JIS) Japanese Industrial Standards, (NEMA) National Electrical Manufacturers Association.
Rectangular cross-section wires are better in fill factor, efficiency and heat dissipation. However there are some applications where the winding is such that rectangular wires cannot be used.
The concept of testing pin holes is – having current flow through the wire and seeing if the insulation is weak at any point resulting in pin holes or leakage of current that was flowing through the wire.
Insulation not being uniform, Quality of conductor being bad (not smooth, or excessive metal dust), Curing of enamel being NG (not good – over or under curing), Improper insulation material, Dust or foreign particle in the process, External Damage to the wire.
The former is used for transmission and latter for conversion from one form to the other.
The classes of insulation for both copper and aluminum are the same by definition. Some classes of insulation in cu don’t have corresponding standards in al, possibly because aluminum winding wire is relatively new and standards are being created and revised as per requirement.
1. The size of the motor would go up in aluminum as to get the same resistance the size of aluminum wire would be more by 25-30% given the same length
2. Making end connections in aluminum requires more precautions as aluminum is brittle and breaks easily when exposed to atmosphere
3. Winding speeds in aluminum are lower as it has poorer tensile strength.
This is the temperature at which wire properties stay intact, when subjected to this temp for over 20,000 hours. After that the wire properties – thermal and electrical start deteriorating and insulation may rupture under electrical and/or thermal stress.
This depends on the enamel type. Normally for making thin wires we need to use enamel with lesser solid contents and for thicker wires enamel with more solid contents is recommended.
Broadly the process is extrusion of wire to the required dimension and then application of liquid enamel. This wire then goes inside an oven and enamel gets cured. The insulation is normally added in multiple no of passes and the wire goes in and comes out of the same oven in tandem in a continuous process till we get the required insulation.
No coating thickness does not depend on class of insulation and can be specified by the user.
Hardness as perceived by the user of wire is problem in wind ability and wire not fitting in the slot properly. It is a combination of inadequate annealing and friction coefficient of the wire.
Tubing is when we break the wire with sudden jerk, we can see conductor under the enamelled wire. It happens due to inadequate adhesion between the wire and the wire enamel.
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.
These wires have the ability to be soldered without removing the enamel as an intermediary step. Self solderable wires when dipped in solder bath at a particular temperature results in removal of enamel and soldering in 1 step hence eliminating a bottleneck in production and making it convenient especially where there are multiple end connections. Also the chances of wire breaking in case of mechanical enamel removal are eliminated.
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.

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