A complete guide to electrical cable
A deeper look into electrical cable.
Electrical cables form an essential part of any building, distributing power to every floor and room. They are designed to cater for different voltages and current loads, and because of this, careful planning is required when it comes to design and installation.
What are the common components of an electrical cable?
Electrical cables are designed to carry electrical energy from its source, such as a consumer unit or distribution board, to the device or application that requires the energy, and are typically made up of three components: a conductor, insulation and sheath.
Conductor
The conductor is responsible for transporting the electric current and is typically made of copper due to its high conductivity, low resistivity and pliability. Copper has the highest conductivity of all the non-precious metals, making it a popular choice. To make it pliable, the copper is annealed after it is drawn to make it less brittle and more pliable, so it is easier to work with. This makes it easier for the installer to route the cables under floors, above ceilings and within walls.
Read more about the benefits of copper conductors.
Aluminium is also a popular metal for conductors, as it is both cheaper and lighter than cooper. However, it is less conductive than copper. An aluminium conductor has just 61% the conductivity of the same sized copper conductor, so aluminium needs a larger size to match copper.
Conductors can either be solid or stranded. Solid conductors are referred to as Class 1 conductors. They are made from a single wire or rod. Stranded conductors are where multiple smaller wires are twisted together. These conductors called Class 2, provide more pliability, so they are ideal in small spaces or applications where the cable needs to bend in a tighter radius than a Class 1. Flexible conductors are made from multiples of even smaller wires, they are called Class 5 conductors and are used in applications where even greater flexibility is needed.
Insulation
The insulation is a layer of dielectric material that covers the conductor, preventing energy loss and ensuring safety. Low voltage Insulation is commonly made from Polyvinyl Chloride (PVC), which is an effective material for electrical and physical protection. It is commonly used as insulation and sheathing in standard building cables such as Prysmian Twin and Earth cable and has a maximum working temperature of 70°C – a requirement of standard building cables.
In applications where a higher conductor temperature is required (above 70°C) then the cable chosen should be insulated with thermosetting material such as cross-linked polyethylene (XLPE). XLPE insulation has greater ductile strength, elongation and impact resistance. Additionally, it will not melt or drip at higher temperatures, up to 90°C.
Sheath
The sheath is the outermost layer of the cable. It is designed to protect the more fragile inner insulation layers cable from environmental factors including moisture, UV radiation, abrasion and impact. Typically, PVC is the material of choice, but it depends on the cable’s application. For example, PVC is ideal for general use, however, in areas where smoke and acid gas could pose a major hazard to people in buildings in the event of a fire to people in buildings, low smoke zero halogen (LSOH) cables should be used. LSOH cables emit less than 0.5% hydrogen chloride and releases a small amount of white smoke, compared to conventional PVC cables – allowing occupants to exit more safely.
Types of electrical cable
Armoured cable
There is a diverse range of electrical cables available.
Low Voltage Cables
Low Voltage (LV) cables are typically used in residential and light commercial applications and is designed for use with a voltage rating between 50V and 1000V for alternating currents (AC), and between 75V and 1500V for direct current (DC).
Medium and High Voltage Cables
Medium voltage (MV) cables are typically designed for 11 kV, 22 kV and 33 kV circuits, and high voltage cables are typically for 66 kV, 132 kV circuits. Extra high voltage cables include 275 kV, 400 kV and above. The most common applications for these cables designed to withstand higher electrical loads power distribution and transmission for electricity network operators.
Armoured Cables
In applications where the cable is vulnerable to the harsh outdoor environments or at risk of physical damage, the cable should have a protective metal layer. Armoured cables are power or control cables designed for 600/1000V mains supply electricity. Examples include Prysmian BS 5467, which is ideal for outdoor power cable applications and Prysmian BS 6724, which is designed for use inside public buildings.
Flexible Cables
Used in portable appliances, electronic devices, automated machinery and much more, flexible cables are lightweight and flexible. These are not required to be fixed in position, which makes it easier to move and reposition appliances as needed.
Specialised cables
Coaxial and data cables also fall under the electrical cable umbrella. Coaxial cables, sometimes referred to as TV aerial cable, transmit high-frequency signals between aerial and satellite dish and TV. Data cables such as ethernet cables, are used for a range of purposes such as connecting hardware and charging. These cables can transmit data and power between devices.
Understanding the relevant parts an electrical cable is crucial for selecting the right cable for the project. It helps to ensure that your electrical systems are safe and running at the optimal performance.
Learn more about Prysmian electrical cables.