Description

Polyesterimide Enamelled Round Copper Wire, Class 180

Most magnet wire datasheets lead with thermal class. Industrial winding failures rarely come from steady-state overheating.

Cores fail because the film was thinned by tension during winding, scuffed by a guide, displaced by short-circuit force, or cracked by a rapid thermal cycle. By the time the winding runs hot enough to matter thermally, the damage has usually already been done - during manufacture, or during the first fault the unit survived.

Class 180 polyesterimide enamelled copper wire - EIW / QZY, GB/T 6109.5, IEC 60317-8, NEMA MW 30-C and MW 72-C, 0.08–3.50 mm - is specified for industrial motors and medium power transformers because the film survives all four of those loads. A class 130/155 polyester film, which is the correct and cheaper choice for steady low-stress duty, starts to give up on them much earlier.

Four ways a winding actually fails

Polyester Enamelled Round Copper Wire for motor

Polyester Round Copper Wire for transformer

1. Winding tension and mandrel bending

An automatic winder pulls wire at constant tension through a path with corners in it. At every corner the film on the inside of the bend is compressed and the film on the outside is stretched. If adherence is marginal, that stretch becomes a local thinning - and a thinned film where two turns sit at different potentials is a turn-to-turn breakdown waiting for the first surge.

This is why the relevant test is flexibility and adherence after mandrel bending, not tensile strength: the conductor is not what fails. The film leaves the metal.

2. Abrasion at the guides and slot edges

Wire runs across felt, ceramic guides and slot edges at speed. Each contact removes a small amount of film, and it removes it at the point where the electric field is highest - the slot, where turns are packed closest together.

A scuffed film passes a continuity test. It fails at hipot, or it fails in service after moisture and contamination find the thin spot. The scrape test exists because this damage is invisible until it is expensive.

3. Cut-through under short-circuit pressure

A through-fault compresses the winding radially and axially, and adjacent turns press against each other with force proportional to the square of the current. At the same time the winding is hot, so the film is at its softest.

If the film yields, two turns touch. The result is a shorted turn that no routine factory test detects - the unit passes, ships, and fails years later when the shorted turn overheats. Cut-through resistance at temperature is the property that decides this, and it is why class alone is a poor specification: two wires of the same class can differ substantially here.

4. Thermal shock cracking

A power tool stalls, a load steps, a contactor chatters. The winding heats in seconds and cools in minutes, and the film has to follow a conductor that moves more than it does.

A film with poor heat-shock resistance cracks at the bend on the first severe cycle. The crack starts on the outside of the bend, where the strain is highest, and it propagates under the varnish so that nothing is visible from the outside.

Where class 180 is specified

Application	The risk that forces class 180
Class H industrial motors	Continuous high hot spot combined with cyclic mechanical stress
Medium and large power transformers	Short-circuit compressive force and heavy winding tension
Power tool windings	Rapid thermal cycling from stall and sudden load changes
Motor rewind work	The replacement must match the original insulation system or the service life changes

A note on class F nameplates. Many motors rated class F (155 °C) are wound with class 180 wire. That is not an overload practice - it is design margin, and it is standard industry practice. The 180 rating covers the transient the nameplate does not describe: the short circuit, the stall, the cooling failure, the hot day. If someone proposes downgrading a class F motor to class 155 wire to save cost, the saving is real and the margin is what disappears.

Application

For motor

For coil

The rewind shop detail

Class 180 polyesterimide strips cleanly and takes solder at normal iron temperatures once stripped, which is what makes it practical on a rewind bench. It is not self-solderable - unlike polyurethane (UEW) wire, the film has to be removed mechanically or chemically before the joint is made.

If the original winding used a polyamide-imide overcoated wire (polyester(imide) Overcoated with Polyamide-Imide Enamelled Copper Wire, Class 200/220), expect the film to resist stripping and plan for mechanical removal. Confirming which construction the motor was originally built with is worth two minutes before a rewind is quoted: the labour difference between the two is significant, and a quote based on the wrong one is a loss on the job.

Specification

Caption: Class 180 polyesterimide enamelled round copper wire (EIW) - 0.08–3.50 mm.

Item	Specification
Type designation	EIW - QZY
Thermal class	180 (Class H)
Standard	GB/T 6109.5-2008, IEC 60317-8, NEMA MW 30-C / MW 72-C, JIS C3202
Conductor	Copper, round, annealed
Size range	0.08–3.50 mm
Properties	Thermal stability, insulation and abrasion resistance, solvent resistance
Enamel build	Grade 1, 2, 3
Enamelling passes	10–13
Spools / net mass	PT-4, PT-10, PT-15, PT-25, PT-30, PT-60 - wooden or to request
Typical applications	Class H motors, medium and large power transformers, power tool windings

Test schedule for every batch

Every delivery is accompanied by a batch test report covering:

Group	Tests performed
Conductor	conductor diameter and tolerance, elongation, springback
Film	enamel build, continuity of covering, flexibility and adherence, heat shock, cut-through, scrape resistance, adhesion
Electrical	breakdown voltage, electrical resistance, tangent delta
Chemical	solvent resistance