Nomex aramid paper insulated round conductor

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Round Copper Conductor

For round copper conductors with Nomex paper insulation, we manufacture diameters ranging from 1.0 mm to 7.0 mm as a standard offering. Some suppliers extend this range up to 10.0 mm for larger conductor requirements. The copper used is high-purity electrical grade material, typically oxygen-free, with conductivity exceeding 100% IACS.

Alternative sources indicate round conductor diameters can start from as small as 0.85 mm up to 6.00 mm, with the precise range dependent on the specific standard being followed. For applications requiring even smaller diameters, some manufacturers offer round Nomex insulated wire from 0.3 mm upwards.

Round Aluminium Conductor

For aluminium conductors, the typical diameter range is 1.0 mm to 7.0 mm for round profiles. The aluminium material is high-purity electrical grade, offering approximately 62% IACS conductivity while providing significant weight advantages—aluminium has only 30% of the density of copper. Extended ranges of 1.9 mm to 10.0 mm are also available from some manufacturers for larger diameter requirements.

Diameter Tolerances

Precision in conductor diameter is essential for consistent electrical and thermal performance. We maintain tight dimensional tolerances through precise drawing processes, with typical tolerances in accordance with IEC and NEMA standards. The diameter tolerance is particularly critical for ensuring uniform paper covering thickness and consistent winding geometry during transformer coil manufacturing.

Nomex Paper Insulation Specifications

Paper Types and Grades

The most widely used grade for conductor insulation is Nomex® Type 410, which is a calendered insulation paper offering high inherent dielectric strength, mechanical toughness, flexibility, and resilience. Type 410 is produced in multiple thicknesses ranging from 0.05 mm (2 mil) to 0.76 mm (30 mil), with specific gravities from 0.7 to 1.2 depending on the thickness and density requirements.

Nomex® 358 is a newer grade specifically optimized for wrapped conductor insulation applications in thermal classes up to 180°C, such as dry-type transformers. It is currently available in a 0.05 mm (2 mil) thickness and features a more open structure that allows for good impregnation.

Tape Thickness

The most common tape thickness used for wrapping conductors is 2 mil (0.05 mm), which corresponds to Nomex 358 or thin-gauge Type 410 paper. For applications requiring greater insulation build, thicker paper grades such as 3 mil (0.076 mm) or thicker can be specified.

Construction and Layering

The standard construction recommended for Nomex paper insulated round conductors utilizes two tapes with 50% overlap, providing complete coverage and robust dielectric protection. The minimum overall increase in insulation thickness for 2 mil tape in a two-tape, 50% overlap configuration is approximately 7 mil (0.178 mm) per NEMA MW 1000-2018, with a typical increase of 8 mil (0.203 mm) in total build.

For applications requiring enhanced dielectric strength, additional layers can be applied. Manufacturers offer configurations ranging from single layer to eight layers, with wrapping directions specified as same direction or opposite direction depending on the application requirements. For high-voltage applications up to 36 kV, the number of paper layers should be increased accordingly.

Thermal Performance

Temperature Rating

Nomex paper insulated round conductors are officially classified as 220°C insulating materials by Underwriters Laboratories (file E34739) and recognized by major institutes worldwide. The 220°C thermal class represents the maximum continuous operating temperature at which the insulation maintains its electrical and mechanical properties.

Alternative thermal classes are also available depending on the specific Nomex grade selected. Some suppliers specify 180°C (Class H) or 200°C (Class C) ratings for certain configurations. The UL-recognized insulation systems incorporating Nomex provide designers with confidence in the material’s long-term thermal stability.

Thermal Endurance

Even under continuous exposure to temperatures of 220°C, Nomex paper maintains its properties for at least 10 years. This exceptional thermal endurance makes Nomex insulated round conductors suitable for applications where conventional insulation materials would rapidly degrade.

Electrical Properties

Dielectric Strength

The dielectric strength of Nomex paper insulated round conductors is one of its most significant performance attributes. For Nomex 410 paper, the AC rapid rise dielectric strength is approximately 22 kV/mm (559 V/mil) when tested per ASTM D149. For Nomex 358 paper, the value is approximately 17 kV/mm (430 V/mil).

When evaluating the finished wire product, the dielectric breakdown requirement is not less than 300 V/mil of the minimum thickness of paper covering one side, or half the minimum increase in build, per NEMA MW 1000-2018. The breakdown voltage typically exceeds 1500V for standard Nomex wrapped configurations.

Dielectric Constant and Dissipation Factor

Nomex paper exhibits a dielectric constant of 1.6 at 60 Hz, which is significantly lower than many other insulation materials. This low dielectric constant contributes to reduced capacitance in winding systems. The dissipation factor is approximately 0.0050 at 60 Hz.

Resistivity

The volume resistivity of Nomex paper is exceptionally high at 2.00 × 10¹⁶ ohm-cm, while surface resistivity measures 2.00 × 10¹⁶ ohm per square. These values indicate the material’s excellent insulating properties and resistance to leakage currents.

Recommended Working Stresses

For long-term reliability, DuPont recommends that continuous electrical stresses in transformers should not exceed 1.6 kV/mm to minimize the risk of partial discharges (corona). In applications where there is high potential for frequent line voltage surges or other abnormal conditions, continuous working stresses should be kept below 1.2 kV/mm for maximum equipment life expectancy.

Mechanical Properties

Tensile Strength and Elongation

Nomex paper provides good mechanical strength essential for withstanding the stresses of conductor winding operations. For Nomex 358 paper (0.056 mm thickness), typical tensile strength is 36 N/cm in the machine direction and 18 N/cm in the cross direction. Elongation is approximately 9.0% in the machine direction and 6.5% in the cross direction, indicating good flexibility for wrapping processes.

For Nomex 410 paper (3 mil thickness), tensile strength at break is approximately 82.6 MPa in the machine direction and 40.6 MPa in the cross direction, with elongation of 11% and 8% respectively.

Tear Strength

Tear strength is a critical property for paper during the wrapping process. For Nomex 358 paper, initial tear strength measures 10.0 N in the machine direction and 5.5 N in the cross direction. Nomex 410 exhibits higher tear resistance, with 16.0 N in the machine direction and 8.0 N in the cross direction.

Compliance and Standards

Nomex aramid paper insulated round conductors are manufactured to multiple international standards to ensure quality and compatibility. Primary standards include:

• IEC 60317-27 (Paper tape covered winding wires)

• IEC 60317-52 and IEC 60317-53 (Specific to Nomex tape covered wires)

• NEMA MW 33-C and MW 60-C (US standard for aramid paper covered wires)

• GB 7673 (Chinese national standard for paper covered wires)

Most manufacturers also maintain ISO 9001 quality management certifications to ensure consistent product quality.

Packaging and Supply

Nomex paper insulated round conductors are typically supplied on wooden or plastic spools, with common packing weights ranging from 30 kg to 150 kg per spool. Larger spools may be available upon request for high-volume applications.