What is Electrical Conductivity?

Electrical conductivity is a measure of the amount of electrical current that can be carried by material or its ability to carry a current. Electrical conductivity is often known as specific conductivity. Conductivity is one of the basic properties of a material.

electrical conductivity

Electrical conductivity units

The symbol σ denotes electrical conductivity and has SI units of siemens per meter (S/m). The Greek letter κ is used in electrical engineering. Often the Greek letter γ represents conductivity. In water, conductivity is sometimes reported as a specific conductance, which is a measure compared to that of pure water at 25°C.

Electrical Conductivity of Metals

Metals conduct electricity by allowing free electrons to flow between atoms. These electrons are not bound to a single atom or a covalent bond. The movement of one free electron inside the lattice dissipates those in the next atom as charges repel each other. The process repeats itself, moving in the direction of the current towards the positively charged end.

Conduction in metals follows Ohm’s Law, which states that the current is directly proportional to the electrical field applied to the metal. The rule, named after the German physicist Georg Ohm, originated in a published paper in 1827 describing how electrical circuits determine current and voltage. The key variable in the implementation of the Ohm Law is the resistance of metals.

Resistance is the opposite of electrical conductivity, determining how strongly a metal resists electrical current movement. This is generally measured around opposite sides of a one-meter cube of material and represented as an ohmmeter. Resistance is also expressed by the Greek letter rho (ρ).

Material Conductivity 

σ(S/m) at 20°C

Resistivity 

p(Ω•m) at 20°C

Silver 6.30×10⁷ 1.59×10-8
Copper 5.98×10⁷ 1.68×10-8
Annealed Copper 5.80×10⁷ 1.72×10-8
Gold 4.52×10⁷ 2.44×10-8
Aluminum 3.5×10⁷ 2.82×10-8
Calcium 2.82×10⁷ 3.36×10-8
Beryllium 2.500×107⁷ 4.00×10-8
Rhodium 2.23×10⁷ 4.49×10-8
Magnesium 2.15×10⁷ 4.66×10-8
Molybdenum 1.914×10⁷ 5.225×10-8
Iridium 1.891×10⁷ 5.289×10-8
Tungsten 1.82×10⁷ 5.49×10-8
Zinc 1.682×10⁷ 5.945×10-8
Cobalt 1.60×10⁷ 6.25×10-8
Cadmium 1.46 10⁷ 6.84×10-8
Nickel (electrolytic) 1.46×10⁷ 6.84×10-8
Ruthenium 1.31×10⁷ 7.595×10-8
Iron 1.17×10⁷ 8.54×10-8
Platinium 9.44×10⁶ 1.06×10-7
Palladium 9.28×10⁶ 1.08×10-7
Tin 8.7×10⁶ 1.15×10-7
Selenium 8.35×10⁶ 1.197×10-7
Tantalum 8.06×10⁶ 1.24×10-7
Niobium 7.66×10⁶ 1.31×10-7
Steel (cast) 6.21×10⁶ 1.61×10-7
Chromium 5.10×10⁶ 1.96×10-7
Lead 4.87×10⁶ 2.05×10-7
Vanadium 3.83×10⁶ 2.61×10-7
Uranium 3.48×10⁶ 2.87×10-7
Antimony 2.55×10⁶ 3.92×10-7
Zirconium 2.44×10⁶ 4.105×10-7
Titanium 1.798×10⁶ 5.56×10-7
Mercury 1.044×10⁶ 9.58×10-7
Germanium 2.17 4.6×10-1
Silicon 1.56×10-3 6.40×102

Materials with Good and Poor Electrical Conductivity

In metals, Electric conductors include movable electrically charged particles referred to as “electrons.” As the electrical charge is applied to the metal at specific points, the electrons shift and allow the electricity to pass through. Materials with high electron mobility are good conductors, and low electron mobility materials are not good conductors, instead referred to as “insulators.”

Conductors vs Insulators

The conductors are materials or substances that allow electricity to flow through them. They conduct electricity because they allow electrons to flow smoothly from atom to atom within them. The conductors also allow the transmission of heat or light from one source to another.

electrical conductivity aluminum copper

Most metals like copper, aluminum, iron, gold, and silver are strong electricity conductors since electrons are free to pass from one atom to another. Copper, for example, is a strong conductor because it predicts the free movement of electrons very easily. Aluminum, on the other hand, is also a fair conductor but not as strong as copper. It’s very lightweight, so it’s mainly used in power distribution cables. 

Insulators are materials or substances that resist or do not allow the current to pass through them. In general, they are of a solid nature. Insulators are often used in several systems as they do not allow the heat to flow. Resistivity is the property that makes the insulators distinct from the conductors.

Wood, cloth, glass, mica, and quartz are excellent examples of insulators. Insulators are also protectors. They provide protection against the heat, the sound, and of course, the passage of electricity. Furthermore, the insulators do not have any free electrons. That’s the main factor why they’re not conducting electricity.

Copper vs Aluminum

Conductors have different properties such as conductivity, tensile strength, weight and environmental exposure.

No. Property Copper(Cu-ETP) Aluminium(1350) Units
1 Electrical conductivity (annealed) 101 61 %IACS
2 Electrical resistivity (annealed) 1.72 2.83 mOhm-cm
3 Thermal conductivity at 20°C 397 230 W/mK
4 Coefficient of expansion 17 x 10-6 23 x 10-6 /°C
5 Tensile strength (annealed) 200-250 50-60 N/mm2
6 Tensile strength (half-hard) 260-300 85-100 N/mm2
7 0.2% proof strength (annealed) 50-55 20-30 N/mm2
8 0.2% proof strength (half-hard) 170-200 60-65 N/mm2
9 Elastic modulus 116-130 70 N/mm2
10 Fatigue Strength (annealed) 62 35 N/mm2
11 Fatigue Strength (half hard) 117 50 N/mm2
12 Specific heat 385 900 J/kgK
13 Density 8.91 2.7 g/cm3
14 Melting Point 1083 660 °C

Copper

Copper is one of the oldest recognized materials in the world. Its ductility and electrical conductivity have been studied by early electrical experimenters such as Ben Franklin and Michael Faraday. Copper was the conductor used in inventions such as telegraph, telephone, and electric motors.

With the exception of silver, copper is the most common conductive metal, and it has become the international standard. The International Annealed Copper Standard (IACS) was developed in 1913 to equate other metals’ conductivity with copper. 

In addition to copper’s superior conductivity, the metal contains high tensile strength (tensile strength of copper is around 200-250 N/mm2 compared to 50-60N/mm2 of Aluminium) , thermal conductivity, and thermal expansion properties.

Aluminum

While copper has a long history as a material of choice for electricity, aluminum has certain advantages that make it desirable for specific applications.

Aluminum has 62% of copper conductivity but just 30% weight of copper. This means the bare aluminum wire, which has the same electrical resistance, weighs half as much as the bare copper wire. Aluminum is usually cheaper compared to copper conductors.

Aluminum has a standard tensile strength between 40 MPa and 700 MPa. The mechanical strength of aluminum can be improved by cold working and alloys. Copper, magnesium, silicon, manganese, and zinc are used as alloy elements. Aluminum does not become brittle at low temperatures and maintains its ductility.

Copper vs Aluminum Cables and Wires

There are two metals widely used to make electrical cables; copper and aluminum. Copper metal is used to form an insulated electrical copper cable, and aluminum metal is used to create an aluminum cable.

Copper cable is commonly used for electrical wiring due to its high electrical conductivity. It has a high electrical conductivity that makes the passage of electricity without heating too much since it generates less charge when the electricity passes through it. Electrical charges in copper metal pass quickly, so that electrical copper cables are preferred.

One specific disadvantage of the copper cable is that the copper cable is shielded from rubber, making it impossible to detach from the cable. Manufacturers changed copper wire insulated rubber with copper tin wire. However, because of the high copper wire cost, it is not commonly used in residential wiring.

Aluminum wire was introduced as an alternative to traditional copper wire because the aluminum wire is cheaper. Aluminum is a strong conductor of electrical current. Aluminum wire is used for substantial circuit loads, including air conditioning systems, for some residential purposes. Aluminum is also used in a variety of appliances. It has been known to have strong corrosion resistance, which is an excellent aid in ensuring a longer life for all electrical devices made of aluminum wire. It is also an effective and cost-effective solution.

However, aluminum metal still has its drawbacks, as it produces more heat than copper wire due to its high resistance. Aluminum is still being used because the world has an ample supply of this kind of metal.

Conclusion

When considered on a percentage basis, aluminum is the most recycled industrial metal with 75% of aluminum ever produced still in use today. For copper, this number is 65%.  With this in mind, aluminum is arguably a more sustainable option as it is less reliant on non-eco mining and extraction processes and can its recycling processes produce less energy waste.

Whilst both aluminum and copper are 100% recyclable, differences in how each metal is recycled and mined impact the environmental sustainability.

Aluminum has 61% of the conductivity of copper, but has only 30% of the weight of copper. That means that a bare wire of aluminum weighs half as much as a bare wire of copper that has the same electrical resistance. Aluminum is generally cheaper when compared to copper conductors.