Conducting materials are classified into two different categories
- Low resistivity materials
- High resistivity materials
Low resistivity conducting materials
Low resistivity materials or high conductivity materials mean those materials which have high conductivity or low resistivity. Generally good electrical conductors are this type of material.
Read More: What is a conductor
Low resistivity materials are used in transformer winding, in-house wiring as conductors for power transmission and distribution, and in machines like motors, generators, etc. Copper, aluminium, gold, and silver are examples of low resistivity materials. But commercially copper and aluminium are most commonly used. Silver and gold both are also good conductors of electricity but due to their high prices, they are not feasible to use commercially.
Low resistivity electrically conducting materials possess few following additional properties:
Low-temperature coefficient means that the change in resistance with a change in temp. should be low.
But wait! Why is it necessary?
It is necessary to avoid variations in voltage drop and power loss with changes in temperature.
It is a property of the material that allows a material to be drawn or plastically deformed without fracture into thin wire. This property is important because conducting materials are required in different sizes and shapes so they should be ductile enough to be drawn into different shapes and sizes.
Mechanical strength of a material is required because in many applications conductors experience many stresses which may create some difficulties or maybe the complete failure of the devices
There are the following stresses experienced by the materials:
- Overhead line conductors used for transmission and distribution of electrical power are subject to stresses due to wind and their weight.
- When the coils for winding of transformers, motors, and generators are made on formers, the conducting material is subject to mechanical stresses.
Resistance to corrosion
In many applications conducting materials are used in outdoors. So, the materials should be such that it is not corroded when used in the outdoor atmosphere.
High resistivity conducting materials
High resistivity materials or in other terms low conductivity materials are those materials that possess high resistivity or low conductivity properties. Insulators fall under this category.
Carbon, Tungsten, nichrome, and magnain are high resistivity materials. High resistivity materials are used in all instruments where a high resistance value is required. High resistivity materials are used for making filaments for incandescent bulbs, resistance for heating devices, starters for electric motors, etc.
High resistivity electrically conducting materials possess few following additional properties:
For precision applications like making wire-wound precision resistance and resistance boxes and few others, it is a necessary requirement that the materials used should have very low-temperature coefficient resistance. If the temp. the coefficient is high then it may affect the accuracy of measurements of devices.
The material should be ductile because high resistance materials are required to be made for different shapes and sizes. For eg. In heaters, the starters material used should be thick in size and for precision wire wound resistors it should be thin. Therefore, the material should be capable of being drawn into a wire of different sizes and capable of being coiled.
High mechanical strength
High resistivity materials are used as thin wires in some applications. The wire must be required to have high tensile strength so the wire doesn’t break during operations.
Do not oxide
High resistivity materials are used in many heating appliances, so they should be able to withstand high temp. for a long time without oxidation. This is because if an oxide layer is formed on the material the amount of heat radiation will reduce.
High melting point
The materials should have a high melting point because in applications like starters for electrical motors the materials should withstand high temp. for a long time without melting.