When comparing aluminum cable  with copper cables, one of the key observations is that aluminum cables often require a larger cross-sectional area to carry the same electrical load as copper. This phenomenon is not arbitrary but is rooted in the fundamental electrical and physical properties of aluminum. To understand this in detail, we must examine several aspects, including electrical conductivity, resistance, mechanical properties, and practical considerations in electrical installations.

Electrical Conductivity and Resistance

Electrical conductivity is a measure of how well a material allows electric current to pass through it. It is typically expressed in siemens per meter (S/m). Copper has a higher electrical conductivity than aluminum, which means that, for a given cross-section, copper can conduct more current than aluminum with less resistance.

The conductivity of copper is approximately 58 MS/m (MegaSiemens per meter), while aluminum’s conductivity is about 35 MS/m. This means aluminum is only about 60% as conductive as copper. Consequently, to achieve the same level of conductivity as a copper wire, an aluminum wire must have a larger cross-sectional area to compensate for the lower conductivity.

Electrical resistance is another crucial factor. Resistance in a conductor is given by the formula:

R=ρLAR = ho \frac{L}{A}R=ρAL​

Where:

• $R$ is the resistance,
• $\rho$ (rho) is the resistivity of the material,
• $L$ is the length of the conductor,
• $A$ is the cross-sectional area of the conductor.

Since aluminum has a higher resistivity than copper (approximately 1.68 times that of copper), it naturally has higher resistance for a given cross-sectional area. This increased resistance leads to greater energy losses in the form of heat, making it necessary to increase the wire size to reduce resistance and maintain efficiency.

Current Carrying Capacity and Heat Generation

Due to the higher resistance of aluminum, it generates more heat than copper for the same current load. Excessive heating can lead to safety hazards, insulation damage, and energy loss. To mitigate this, aluminum conductors are typically thicker than their copper counterparts, ensuring that the heat generated does not exceed safe levels.

Aluminum cables, therefore, follow a general rule: if a copper wire has a cross-sectional area of X mm², the equivalent aluminum wire should have about 1.6 times that area to carry the same current safely. For example, if a 10 mm² copper wire is required for a specific application, an equivalent aluminum wire might need to be around 16 mm².

Mechanical Considerations: Strength and Ductility

Apart from electrical properties, mechanical properties also play a role in why aluminum cables need a larger cross-section.

1. Tensile Strength:

   • Copper has a higher tensile strength than aluminum. This means copper wires can endure more mechanical stress, such as pulling forces during installation, without breaking.
   • Aluminum, being softer and more brittle, is more prone to breakage under mechanical stress. To compensate, aluminum wires are made thicker, reducing the likelihood of breakage.

2. Thermal Expansion and Creep:

   • Aluminum expands and contracts more than copper with temperature fluctuations. This property, known as thermal expansion, can lead to loosening at connection points, increasing the risk of overheating and electrical failures.