IT1 U15 - Conductor and Insulator Materials - Complete

CGLI 2330 Certificate in Electrotechnical Technology Level 2 Inst Tech: Unit 202 – Principles of Electrotechnology

Unit 15 – Conductor & Insulator Materials

The College At Clacton Unit 15 Page 1 April 2012

Conductor & Insulator Materials

Unit Aims

By the end of the unit participants should be able to:

List the materials used as conductors across the specialisms within the electrotechnical industry

Syllabus Reference: 2.2.01

Explain the properties and application of conductor materials used across the specialisms within the electrotechnical industry


List the materials used as insulators across the specialisms within the electro technical industry


Explain the properties and application of insulator materials used across the specialisms within the electrotechnical industry


Conductor & Insulator Materials

The electrons of different types of atoms have different degrees of freedom to move around. With some types of materials, such as metals, the outermost electrons in the atoms are so loosely bound that they chaotically move in the space between the atoms of that material by nothing more than the influence of room-temperature heat energy. Because these virtually unbound electrons are free to leave their respective atoms and float around in the space between adjacent atoms, they are often called free electrons.

In other types of materials such as glass, the atoms' electrons have very little freedom to move around. While external forces such as physical rubbing can force some of these electrons to leave their respective atoms and transfer to the atoms of another material, they do not move between atoms within that material very easily.

This relative mobility of electrons within a material is known as electric conductivity. Conductivity is determined by the types of atoms in a material (the number of protons in each atom's nucleus, determining its chemical identity) and how the atoms are linked together with one another. Materials with high electron mobility (many free electrons) are called conductors, while materials with low electron mobility (few or no free electrons) are called insulators.




Conductors Here are a few common examples of conductors:

Silver: is the best conductor available. However, due to its price it is not used widely in the electrotechnology industry. However, being a ‘noble’ metal it is resistant to tarnishing and is widely used on the faces of electrical contacts.

Copper: Is second only to silver as a conductor. However, due to its wide availability, relatively low cost and suitable mechanical characteristics, copper is the most widely used material for conductors from cables to busbars, etc.

Gold: is a good conductor. However, like silver due to its price it is not used widely in the electrotechnology industry. However, again like silver, being a ‘noble’ metal it is resistant to tarnishing and is widely used on the faces of electrical contacts.

Aluminium: is very light and has excellent corrosion resistance as well as being a good conductor (although not as good as copper). Its corrosion resistance is also a drawback as the oxide layer which forms very quickly and forms an insulated layer over the material means it is generally only used for solid core conductors of 16mm2 and above as well as for some large busbars. It is also used for overhead transmission lines in conjunction with steel wire.

Brass: is an alloy of copper and zinc. It is a good conductor and is rigid and hardwearing. As a result it is widely used in the electrotechnology industry for terminal and terminal screws as well as for the pins of plug-tops.

Mercury: is metallic and a conductor and has the characteristic of being liquid at normal temperatures. As a result it is often used in ‘tilt-switch’ movement detectors.

Carbon: is a non-metallic conductor. Because, in the form of graphite, it is fairly soft it is utilised in the electrotechnology industry as ‘brushes’ in, for example, rotating machinery. These are fixed to the casing of the machine and ‘rub’ against a rotating metal part on the rotor. This combination allows the transfer of electricity from stationary to moving parts.

Insulators PVC: or polyvinyl chloride is a thermoplastic polymer. It is a good insulator, as well

as being flexible and cheap, easy to work with and easy to install. However, thermoplastic polymers such as PVC do not stand up to extremes of heat and cold. BS 7671 recommends that ordinary PVC should not constantly be used in temperatures above 60°C or below 0°C.

XPLE: or cross-linked polyethylene is a thermosetting compound. The cable has a high softening temperature, small heat distortion and high mechanical strength under high temperature. XLPE is also lighter in weight than its PVC counterpart.

At high voltage there is a potential of failure because of ‘treeing’, which is when moisture breaks down the insulation. Heat-shrink tubing, which also provides stress control, will aid this situation.




Paper: Dry paper is a surprising but excellent insulator that loses its insulating properties if it becomes wet. Dry paper is hygroscopic (it absorbs moisture), so it must be sealed to make sure there is no contact with the air. Paper-insulated cables are sheathed with impervious materials, lead being the most common.

PILC (paper-insulated lead-covered) has been traditionally used for supply systems, with the paper insulation being impregnated with oil or non-draining compound to improve its long-term performance. Cables of this kind need special jointing methods so that the insulation stays sealed.

Magnesium Oxide: is a white, powdered substance used as an insulator in mineral-insulated cables. This form of insulation is also hygroscopic and must be protected from damp with special seals. Mineral-insulated cables can withstand very high temperatures and, being metal-sheathed, can also withstand a high degree of mechanical damage.

Synthetic rubbers: such as butyl rubber, will withstand high temperatures much better than PVC. They are normally used for the flexible final connection to items such as immersion heaters, storage heaters and boiler house equipment.

For more information see pages 246 to 250 of ‘Installing Electrotechnical Systems and Equipment Book A’ – revised for the 17th Edition Amendment 1 of the IET Wiring Regulations (ISBN 978 0 435 031268).

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IT1 U15 - Conductor and Insulator Materials - Complete