In simple terms, the difference between Soft Drawn and Hard Drawn copper lies in the manufacturing process (specifically "Annealing"), rather than the material itself. Both typically use high-purity electrolytic copper.

Regarding your question about IEC 60228, Class 5 and Class 2 refer to the geometric structure of the conductor, whereas Soft/Hard drawn refers to the physical temper (hardness) of the metal. These are two different dimensions of classification.

1. Soft Drawn vs. Hard Drawn: The Manufacturing Process

The fundamental difference is whether the copper undergoes an annealing heat treatment after being drawn through the dies.

• Hard Drawn Copper:

Process: The copper rod is pulled through a series of dies to reduce its diameter. This "cold working" causes work hardening, where the crystal structure is elongated and internal stresses build up.

Characteristics: High tensile strength (very strong), but stiff and brittle. It resists bending and has a "springy" quality.

• Soft Drawn (Annealed) Copper:

Process: After the final drawing stage, the copper is subjected to a controlled heating process called annealing, then cooled slowly. This relieves internal stresses and allows the crystals to reform.

Characteristics: Very flexible and has high elongation (it can stretch significantly before breaking). Because the crystal structure is restored, its electrical conductivity is also slightly higher than that than hard-drawn copper.

2. Relationship with CONDUCTOR STANDARD IEC 60228 (Class 2 vs. Class 5)

This is a common point of confusion. The conductors defined in IEC 60228 (Class 1, 2, 5, and 6) are almost always made of Soft Drawn (Annealed) copper.

• Why does Class 5 feel "softer" than Class 2?

It is not because the metal state is different (both are annealed); it is because of the geometric structure:

• Class 2 (Stranded Conductor): Made of a few relatively thick strands (e.g., 7 or 19 wires). Because each individual wire is thick, the overall cable is stiffer.

• Class 5 (Flexible Conductor): Made of a large number of very fine wires (often called "fine-wire strands"). Because each individual strand is thin, the entire bundle bends very easily.

3. Comparison Summary

4. Practical Applications

• When to use Hard Drawn:

Mainly used for bare conductors in outdoor environments. For example, overhead power lines on poles require the high tensile strength of hard-drawn copper to support their own weight and withstand wind or ice loads over long spans.

• When to use Soft Drawn:

Used for virtually all insulated cables (building wire, power cables, control cables). Since these cables must be pulled through conduits and bent around corners during installation, hard-drawn copper would be too stiff and would likely crack the insulation.

• Hard Drawn vs. Soft Drawn Copper: Can They Be Used Interchangeably?

In the world of cable selection and electrical engineering, a common question arises: "Since they are both made of high-purity copper, can Hard Drawn and Soft Drawn copper be used interchangeably?"

The short answer is: Usually, no.

While their chemical composition is identical, their physical properties—strength, hardness, and elongation—are vastly different. Attempting to swap one for the other often leads to installation failures or, worse.

①　Why "Soft" Cannot Replace "Hard": The Risk of Sagging

Hard Drawn copper is the primary choice for overhead conductors. It relies on the strength gained from the cold-drawing process to support its own weight and withstand environmental loads like wind, ice, and snow.

The Risk：If you replace hard-drawn copper with soft-drawn (annealed) copper on a power pole, the wire will stretch under its own weight because its tensile strength is roughly half that of hard-drawn copper.

The Consequence：This leads to excessive "sagging." The wires may hang too low to the ground, causing dangerous electrical arcing (flashovers) or snapping entirely during a storm.

②　Why "Hard" Cannot Replace "Soft": Damage to Insulation

Soft Drawn (Annealed) copper is the standard for almost all insulated cables (such as IEC 60228 Class 2 or Class 5) because it is flexible and easy to handle.

The Risk：Hard-drawn copper is incredibly stiff—more like a rod than a wire. If you attempt to pull it through a conduit or bend it within a tight junction box, it will resist every move.

The Consequence：Forcing hard-drawn copper to bend creates immense internal stress that can crack or puncture the insulation from the inside out, leading to short circuits. Additionally, in environments with vibration, hard-drawn copper is far more susceptible to fatigue failure and breakage.

③　The Only "Gray Area": Grounding Systems

In specific grounding and lightning protection systems, you may occasionally see both used, but for different reasons:

Soft Drawn: Preferred by installers because it can be easily shaped to fit the contours of a grounding pit or foundation.

Hard Drawn: Sometimes used for exposed grounding runs where a straight, neat appearance is required or where higher resistance to mechanical impact is needed.

Note: Always defer to the specific engineering specifications provided for the project.

Summary for Procurement and Engineers：

Before placing an order, always verify the mechanical requirements of your application:

For self-supporting outdoor spans, choose Hard Drawn.

For indoor wiring, insulated cables, or flexible connections, always choose Soft Drawn (Annealed).