Class 120 Polyvinyl Acetal Enamelled Round Copper Wire: Specifications and Testing

What Is Class 120 Polyvinyl Acetal Enamelled Round Copper Wire?

Polyvinyl acetal enamelled round copper wire is a type of insulated winding wire in which a round copper conductor is coated with a continuous layer of polyvinyl acetal enamel. The class 120 designation refers to the thermal endurance of the insulation system, indicating that the wire can operate reliably at temperatures up to 120 °C. Class 120 corresponds to class E in the IEC 60085 thermal classification. The thermal class requires a minimum temperature index of 120 and a heat shock temperature of at least 155 °C; the temperature corresponding to the temperature index is not necessarily the recommended continuous operating temperature, which depends on many factors including the type of equipment and the hottest-spot allowance of the design.

Relevant Parameters

The table below summarizes the main parameters of class 120 polyvinyl acetal enamelled round copper wire.

Parameter	Value
Thermal class	120, class E
Specification range	Grade 1: 0.040 to 2.50 mm; Grade 2: 0.040 to 5.00 mm; Grade 3: 0.080 to 5.00 mm
Insulation material	Polyvinyl acetal
Standards	IEC 60317, GB/T, JIS, NEMA
Insulation thickness	Grade 1, Grade 2, Grade 3
Packing	PT-4 to PT-200 reels or plywood spools

Test Requirements per IEC 60317-0-1

IEC 60317-0-1 defines the general requirements for enamelled round copper winding wires, and the specific part for class 120 polyvinyl acetal wire applies to wires with a sole coating based on polyvinyl acetal or polyvinyl formal resin. The resin may be modified provided it retains the chemical identity of the original resin and meets all specified wire requirements. The nominal conductor diameter ranges covered by the document are: Grade 1 from 0.040 mm up to and including 2.500 mm, Grade 2 from 0.040 mm up to and including 5.000 mm, and Grade 3 from 0.080 mm up to and including 5.000 mm.

The principal test requirements are as follows:

Cut-through test: no failure shall occur within 2 minutes at 170 °C.

Flexibility and adherence: clause 8 of IEC 60317-0-1 applies, where the constant K used for the calculation of the number of revolutions for the peel test shall be 175 mm.

Heat shock: clause 9 of IEC 60317-0-1 applies, and the minimum heat shock temperature shall be 155 °C.

For nominal conductor diameters up to and including 1.600 mm, the coating shall show no crack after the specified tests.

Resistance to abrasion applies for nominal conductor diameters from 0.250 mm up to and including 2.500 mm.

Applications

Polyvinyl acetal enamelled copper wire is a crucial material in electrical engineering, known for its excellent insulation properties, durability and ability to withstand elevated temperatures. It is widely used in the winding of small and medium motors, transformers, solenoids, relays and other electromagnetic devices where a balanced combination of thermal endurance, mechanical toughness and good adhesion of the enamel film is required. The good resistance to moisture and the strong bond between the enamel and the copper conductor make it particularly suitable for applications subjected to vibration and winding tension.

Selection and Handling Notes

When selecting class 120 wire, verify the thermal class against the hottest-spot temperature of the finished coil, and choose the insulation thickness grade, Grade 1, 2 or 3, according to the voltage stress and the space factor of the winding. The wire is supplied on reels or spools with different flange diameters, and the packing should protect the wire from mechanical damage and moisture during transport and storage. During winding, the tension and bending radius must be controlled so that the enamel film is not damaged, and the wire should be stored in a dry environment until use.

FAQ

Q: What does class 120 mean for an enamelled wire?

A: It is the thermal class of the insulation system, rated for continuous operation up to 120 °C, with a minimum temperature index of 120 and a heat shock temperature of at least 155 °C per IEC 60317-0-1.

Q: What is the difference between the temperature index and the operating temperature?

A: The temperature index is a value obtained from accelerated aging tests that characterizes the thermal endurance of the insulation, while the recommended operating temperature depends on the equipment type, the hottest-spot allowance and the thermal class of the whole system.

Q: Which standard governs this wire?

A: The IEC 60317 series, principally IEC 60317-0-1 for general requirements and the specific part for class 120 polyvinyl acetal enamelled round copper winding wire; GB/T, JIS and NEMA equivalents are also applied in different markets.

Q: What is the cut-through test?

A: It is a test in which a loaded blade is applied to the coated wire at an elevated temperature to determine the resistance of the enamel film to softening; for this wire, no failure shall occur within 2 minutes at 170 °C.

Q: What insulation thickness grades are available?

A: Grade 1, a thin coating, Grade 2, the standard coating, and Grade 3, a thick coating; the grade is selected according to the voltage stress and the space factor requirements of the winding design.

Q: Is polyvinyl acetal wire suitable for transformer windings?

A: Yes, it is used in the windings of small and medium transformers and other devices; the operating temperature of the winding must be kept within the class 120 limit, taking into account the hottest spot of the coil.