Oxygen-free copper (TU1/TU2) has a purity ≥99.95% with extremely low oxygen content. Many low-cost cables on the market use recycled impure copper or low-oxygen copper to pass off as oxygen-free copper.

1. Color & Cross-Section Observation

✅ Features of Oxygen-Free Copper

• The copper conductor presents an even rose purplish-red hue with fine, mellow metallic luster.
• Cut open the wire to check the cross-section: dense and smooth, free of pores, black spots or sand holes; uniform color from surface to core.
• After stripping the insulation and exposing to air for several hours, it will not develop large-scale oxidation and blackening rapidly.

❌ Inferior Recycled Copper / Low-Oxygen Copper

• Dull color, tending to dark red or yellowish tone.
• Black specks and tiny holes are visible on cross-sections.
• It oxidizes and turns black quickly when exposed to air.
• Some conductors look bright on the surface but appear dark once scraped open.

2. Toughness Test

Cut a section of copper conductor and bend it repeatedly at 180°.

✅ Oxygen-Free Copper

• Flexible with good resilience.
• It will not break after over ten bends.
• No white cracks or peeling at bending positions.

❌ Recycled Impure Copper

• Relatively stiff.
• White fine cracks and brittleness appear after 3–5 bends.
• May even snap directly.

Principle: Impurities and copper oxide make copper brittle.

3. Weight Comparison for Same Specifications

Copper has a fixed density. For wires of identical cross-section and length, oxygen-free copper cables weigh heavier.

Many non-standard cables not only adopt poor-quality copper but also cut down conductor cross-section, resulting in double weight reduction.

4. Markings & Certificates

• Clear printed markings on cable sheath with CCC certification and national standard GB/T 5023.
• Formal major manufacturers can provide test reports indicating oxygen-free copper conductors.
• Beware of low-priced products only labeled "pure copper" or "red copper" without specifying oxygen-free copper.

5. Advanced Simple Tests

Magnet Test

Pure copper is non-magnetic. If a magnet attracts the copper slightly, iron impurities are mixed in the copper; reject such products directly.

Flame Test

Briefly heat the copper wire with a lighter.

• Oxygen-free copper: Only the surface oxidizes and turns black; it remains tough after cooling and does not break easily.
• Impure recycled copper: Turns brittle after heating and can crumble with gentle twisting.

Summary

Identifying genuine oxygen-free copper requires comprehensive evaluation through multiple methods. While visual inspection and simple tests can provide preliminary screening, professional DC resistance testing remains the most reliable verification method. Always purchase from reputable manufacturers with proper certifications and test reports to ensure product quality and electrical safety.