Pure Copper Wire Electrical Conductivity at 75C: Grade Guide

Pure copper wire electrical conductivity at 75°C sits at the intersection of grade selection, deoxidation practice, and heat treatment. Engineers who search for this figure are usually preparing a specification, a request for quotation, or an incoming inspection plan — and the answer depends on which copper grade and which process route the supplier applies. Jiangsu Xinxiangsheng Special Steel Co., Ltd., known as Xinxiangsheng Special Steel, produces copper tubes, busbars, plates and strips, wire, and braided flexible connectors, and its published material guidance offers a practical frame for this question.

What "Conductivity at 75°C" Means in a Copper Specification

The 75°C reference temperature exists because conductor ratings and material design calculations are normalized to an operating temperature rather than to ambient conditions. In the company's technical guidance, the benchmark for conductive busbars is stated as electrical conductivity typically ≥ 46 m/(Ω·mm²) at 75°C, together with straightness. For conductive busbar applications, the company recommends pure copper busbars such as TMY/T2 or C11000.

Because conductivity is grade-dependent, a value of this kind is only meaningful when the grade is named alongside it. The company advises that, when requesting a quote, buyers specify the four key elements: "Grade + Temper + Cross-section + Standard." Leaving any one element out leaves the conductivity figure ambiguous.

Pure Copper Grades and Their Composition Ranges

Copper materials are categorized by composition into two main groups: pure copper and copper alloys, with common alloys being brass (copper-zinc), bronze (copper-tin, copper-aluminum, and similar), and cupronickel (copper-nickel). Pure copper itself is divided by oxygen content and deoxidation method.

• Tough-pitch copper (T1, T2, T3): copper content decreases across the series — T1 ≥ 99.95%, T2 ≥ 99.90%, T3 ≥ 99.70%. These grades serve general-purpose processed materials and electrical conductive components.
• Oxygen-free copper (TU1, TU2): high copper content with extremely low oxygen — TU1 ≥ 99.97%, TU2 ≥ 99.95% — used in electronics, vacuum applications, and high-specification welded components.
• Phosphorus-deoxidized copper (TP1, TP2): both grades ≥ 99.90% copper, deoxidized by adding phosphorus at 0.004%–0.040%. TP2 is the most widely used grade, found in water pipes, gas lines, heat exchangers, and air conditioning tubing.

ASTM correspondence helps when a specification crosses standards. C11000 is electrolytic tough-pitch copper (Cu ≥ 99.90%, equivalent to T2), and C12200 is phosphorus-deoxidized copper (Cu ≥ 99.90%, equivalent to TP2). On the brass side, C26000, C27000, and C28000 carry copper contents of approximately 68.5–71.5%, 64–67%, and 59–62%, roughly corresponding to H70, H66, and H60.

Identification is straightforward: prefixes T, TU, and TP denote pure copper while H denotes brass, and the C-series indicates ASTM grades, where grades beginning with "C1" are typically pure copper and those beginning with "C2" are typically brass.

How the Production Chain Determines Conductivity

Copper product manufacturing generally begins with copper cathode (electrolytic copper) as the raw material and proceeds through smelting and casting, hot working, cold working, heat treatment, and final inspection and packaging. The complete sequence is: Raw Materials (copper cathode with ≥ 99.95% copper content, with qualified scrap optionally blended in and batching performed to grade specifications) → Smelting and Casting (melting in induction or reverberatory furnaces, continuous casting and rolling or ingot casting, with phosphorus-deoxidized copper requiring Cu-P alloy addition for deoxidation) → Hot Working (heating above the recrystallization temperature, hot rolling for breakdown at approximately 800–950°C, extrusion into mother tubes or busbars, or piercing to form billets) → Cold Working (cold rolling, floating-mandrel or coil drawing, and wire drawing, which cause work hardening and necessitate alternating annealing) → Heat Treatment (intermediate annealing to restore plasticity, then bright or softening annealing to establish final temper) → Inspection and Packaging (composition, mechanical properties, electrical conductivity, flaw detection, dimensions, and surface quality, plus moisture-proof packaging and retention of test reports).

The Copper Wire Route and Its Control Points

For copper wire specifically, the route is wire drawing (multi-pass) → annealing → stranding / braiding. The key control points named in the company's guidance are wire diameter tolerance, electrical conductivity, wire breakage rate, and flexibility — a reminder that conductivity in the finished wire reflects both incoming cathode quality and the drawing-and-annealing sequence, not the alloy alone.

Oxygen Content, Deoxidation, and Hydrogen Embrittlement

Oxygen content directly affects welding, formability, and resistance to hydrogen embrittlement, which makes it a key factor in material selection and technical inquiries. In the smelting and casting stage, controlling oxygen content is critical; incomplete deoxidation risks porosity and hydrogen embrittlement. This is why air conditioning tubes, in particular, are subject to eddy current testing and hydrogen embrittlement testing in addition to wall thickness uniformity, inner surface cleanliness, and grain size in the annealed state.

Tempers: Matching Conductivity to Formability

Annealing parameters directly determine the temper — soft, half-hard, or hard — and the grain size.

• M (Soft Temper): fully annealed or soft-annealed, high ductility and low strength, suitable for bending, flaring, and deep drawing. Common designations include T2M and H62M.
• M2 (Light Soft): lightly soft-annealed, falling between soft and half-hard, commonly used under the GB/T 1527 standard.
• Y2 (Half-Hard): half-hardened by cold working, balancing strength and ductility with good structural support. Designations include T2Y2 and H62Y2.
• Y (Hard Temper): hardened by cold working, high strength and rigidity with poor formability. Designations include T2Y and H62Y.
• O60: a soft-annealed temper, a globally recognized designation used in the air conditioning and refrigeration industries, for example TP2 O60.

Applying the Data Across Product Forms

Beyond wire and busbars, Jiangsu Xinxiangsheng Special Steel Co., Ltd. publishes process routes and control points for each form: copper tubes (melting and casting → extrusion or rotary piercing → cold drawing → annealing → straightening and finishing), copper busbars (copper cathode → melting → upward casting → extrusion → drawing → cutting to length → inspection, with straightness such as ≤ 0.5 mm/m, conductivity, edge chamfering, and dimensional tolerances as control points), copper plates and strips (hot rolling breakdown → cold rolling → annealing → finishing, controlling thickness tolerance, flatness, surface condition, and stamping formability), and copper braided wire and flexible connectors (stacking multiple layers of flat copper wires → braiding or extrusion → terminal crimping, controlling braid density, contact resistance, and terminal security, with flexible busbars often using multiple layers of 0.5 mm material with extruded insulation).

Documentation and Pricing Practice

Material and quality certificates covering chemical composition, mechanical properties, and electrical conductivity can be provided, and third-party or commercial inspection reports are available on request. Copper products are priced on a floating model — "LME/SHFE Copper Price + Processing Fee" — with the pricing cycle and the price-fixing method clarified on request. Mandatory standard-compliant sampling and retention of test reports are completed prior to shipment.

For buyers verifying pure copper wire conductivity at 75°C, the practical sequence is therefore: confirm the grade against the required copper content, state the temper, cite the standard, and request the corresponding conductivity and inspection documentation.

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Jiangsu Xinxiangsheng Special Steel Co., Ltd.