Getting in a knot over which wires and cables you need? With hundreds of different types, not to mention the countless applications, choosing the right cable for your next project can seem a bit of a task. There’s huge variation as to how cables and wires are designed, the materials of which they are made, and where they are safe to be used. Knowing the basics will ensure that your wiring is safe and up to current standards.
Cable vs Wire
First, let’s talk about the distinction between wires and cables. When working with wiring, you’ll come across both cables and wires. Wires are single conductors, either bare or insulated, whereas a cable is an assembly of two or more wires inside an insulated jacket. Wires can be solid (cores), or as is more common, consist of multiple strands twisted together. Cables also come in different types, depending on usage. There are power transmission cables, electrical cables, data cables and telephony cables.
Electrical cables are those tasked to transport electricity from one point to another. They are categorised by the voltage they can take into low voltage, medium voltage and high voltage cables. Low voltage cables are those you’d find in domestic wiring and are rated up to 750 Volts. Higher rated low voltage cables, up to 1 kV, are found in many industrial applications, like powering machines and equipment. Medium voltage cables with voltages from 1 to 36 kV are used in power transmission from substations to your home or commercial and industrial premises. And high voltage cables, rated above 36kV, are used to transport electricity from power stations to substations. All will be built differently depending on where they are used, come in various sizes, or gauges, and need to abide by current Australian and international standards.
What Goes in an Electrical Cable
An electrical cable consists of a conductor through which electricity flows, insulation that covers that conductor to ensure there is no leakage, often covered in a protective layer, and finally an outer sheathing. The conductors or wires can be made of copper or aluminium, with copper wires having better conductivity, so is the most common material. Cables can be single-core, having only one conductor, or multi-core with several conductors.
Insulation also differs. There are two basic types. Thermoplastic insulation, with PVC insulation sleeves being the most common, and thermoset insulation, is used in more rigorous environments where there is high heat, exposure to liquids of chemicals, and high mechanical stresses. The latter is also more likely to have some form of metallic protection. Here there are metallic screens or armouring, which shield the electric current from external forces, like strong electromagnetic interference. The jacket, or outer sheath, is the first line against moisture, flames or impact and this also has some level of elasticity. PVC is the most common material here as well, but there are also cables with polyethylene, polyurethane, or thermoset rubber jackets.
Individual wires and cables are sold with designated numbers that inform buyers of the size. In Australia, sizes refer to the maximum diameter of the wires inside a cable. This is stated in mm squared and is part of the name. For example, residential twin and earth cables in 6mm2 will be designated as 6T&E. This also happens to be cabling used for the majority of appliances, like microwaves or blenders. Cables in thicker diameters, like 10 or 16mm2, are used to power more power-hungry appliances like fridges, ovens or air conditioners. Those in thinner sizes (4mm2, 2.5mm2 and 1.5mm2), and often in a solid wire configuration, are used for lighting, USB sockets, and devices needing less power.
In residential wiring, there are two power wires, and an earth wire. The active or live/hot wire transports power from the meter box to the switches and sockets, and from there to appliances. This is brown. The neutral wire is a conductor that helps the current return to the power source, and in the opposite direction from the active wire. This is blue. Between the two is the earth wire, and this provides a low resistance path for the current to the ground. In case of an electrical fault, the earth (or ground) wire redirects the surge in current into the ground instead of the circuit, so electrocution is prevented. This wire is now coloured green and yellow. The wires are set in the aforementioned twin and earth cable, and this is the most common type you’ll see inside Aussie homes. For outdoor uses, a twin and earth cable with more resistant outer sheathing will be more appropriate.
Current colour coding rules came into effect in 2018, so most Australian homes will have a different colour scheme. Something to consider when doing DIY wiring around the house. This is a single-phase power supply. In three-phase electricity used for industrial and commercial installations, there are 2 or 3 active wires, coloured brown, black (or grey), with the neutral being black, and the earth green and yellow.
Residential electrical cables are mostly sold as twin and earth, or twin flat cables in smaller diameters. They consist of a solid or stranded wire, housed in PVC insulation in the appropriate colours, and an outer white jacket. Electrical retailers will also have coaxial data and telephony cables used in transmitting signals in NBN and telephone lines.