In electrical engineering, the selection of conductor materials for electric wires and transmission lines depends not only on electrical properties but also on mechanical strength. One important mechanical property is the Ultimate Tensile Strength (UTS) of the conductor material.
Copper and aluminium are the two most commonly used materials in electrical conductors. Their ultimate tensile strength determines how much mechanical load the conductor can withstand before breaking.
Table of Contents
What is Ultimate Tensile Strength?
Ultimate Tensile Strength (UTS) is defined as the maximum stress that a material can withstand while being stretched or pulled before it breaks.
Mathematically,
\[
\text{UTS} = \frac{\text{Maximum tensile force}}{\text{Original cross-sectional area}}
\]
The unit of tensile strength is typically:
- MPa (Mega Pascal)
- N/mm²
Ultimate Tensile Strength of Copper
Copper is widely used in electrical wiring, cables, motors, and transformers
due to its excellent electrical conductivity.
Typical Value
The ultimate tensile strength of annealed copper used in electrical conductors is approximately:
\[
UTS_{Cu} \approx 200 \; \text{MPa}
\]
(Approximately 200 N/mm²)
Characteristics of Copper
- High electrical conductivity
- Good ductility
- High mechanical strength
- Good resistance to fatigue and corrosion
Because of its relatively higher tensile strength, copper wires are less likely to break under mechanical stress.
Ultimate Tensile Strength of Aluminium
Aluminium is widely used in overhead transmission lines because of its
low weight and lower cost compared to copper.
Typical Value
The ultimate tensile strength of aluminium used in electrical conductors is approximately:
\[
UTS_{Al} \approx 90 \text{ to } 150 \; \text{MPa}
\]
(Approximately 90–150 N/mm²)
Characteristics of Aluminium
- Low density (lightweight)
- Lower cost
- Good corrosion resistance
- Adequate electrical conductivity
However, aluminium has lower tensile strength compared to copper, which means it is mechanically weaker.
Comparison of Copper and Aluminium
| Property | Copper | Aluminium |
|---|---|---|
| Ultimate Tensile Strength | ≈ 200 MPa | ≈ 90–150 MPa |
| Mechanical Strength | Higher | Lower |
| Weight | Heavy | Light |
| Electrical Conductivity | Higher | Lower |
| Cost | Higher | Lower |
From the comparison, copper is mechanically stronger, but aluminium is lighter and cheaper.
Importance in Electric Wires
Copper Conductors
Copper is commonly used in:
- Domestic electrical wiring
- Electric motors
- Transformers
- Electronic circuits
Its higher tensile strength provides better mechanical reliability.
Aluminium Conductors
Aluminium is commonly used in:
- Overhead transmission lines
- Power distribution lines
- ACSR (Aluminium Conductor Steel Reinforced) cables
Because aluminium has lower tensile strength, steel reinforcement is often added to increase mechanical strength.