Live, neutral, earth – is it that simple?

The live core, or the phase conductor is normally required to have brown coloured insulation or marked as brown if a different colour. The neutral core acts as the return path for current and completes the circuit, these are expected to be blue in colour, or marked as blue. The circuit protective conductor (CPC) is designed to carry a fault current should one occur and in turn is connected to the circuit protection devices. The CPC may or may not be insulated depending upon the system design, but we commonly see CPC earth conductors insulated with two colours, normally green and yellow. 

 

Single-phase circuits use the live and neutral. The live carries current or load, and the neutral core provides a path for the return current. Most residential homes require single-phase supply only because they require small amounts of power for applications such as domestic lighting and heating circuits. Single-phase common voltage starts at 230V with a possible spread of up to 254V and the oscillation frequency approximates to 50Hz – 50 cycles per second. 

 

Cables, no matter in what application, need electrical insulation. In the past, this has been paper wrapped around the conductor and for HV overhead lines the insulation is still in the air! The most common electrical insulation today is however PVC (Polyvinyl Chloride). It is an excellent material that when mixed or compounded correctly with right ingredients by experts, provides effective electrical and physical protection. For example, it is ideal for insulating and sheathing Prysmian “twin and earth” cable. The insulation isolates and prevents direct contact between conductors, and between a conductor and its environment. However, if a higher conductor temperature is required, then consider using cables insulated with XLPE instead. 

 

What’s the difference? PVC is a thermoplastic material and has a maximum working temperature of 70°C, which is just what is required by the wiring regulations for standard building cables. However, cross linked polyethylene cable, often abbreviated to XLPE, has a maximum working temperature of 90°C due to its thermoset material. This means conductors that are insulated with XLPE can run a higher temperature than if it were insulated with PVC. Depending upon the circuit design, this higher temperature means higher current and so more energy can be delivered for any given size conductor.

The long chain polyethylene molecules are cross linked, or chemically bonded together, to make a complex, 3D network. This makes the material tougher, stronger, and more resistant to aging and cracking, providing overall stability of the cable – it has a higher deformation resistance to heat.

 

The cable’s sheath is also important. This is the outer extruded material that holds all of the inner parts together. PVC is the most common sheath type for a number of reasons. It’s readily available, easy to manufacture and handle, and the cable is typically more pliable, especially at lower temperatures. However, in the event of fire in a building such as a shopping centre or a hospital, PVC burns and produces thick black smoke, hydrochloric acid, and other toxic gases, which is a risk to public health and emergency equipment. 

A Low Smoke Zero Halogen (LSOH) sheath on the other hand, produces very low levels of smoke and no acid gases in the event of fire, this makes LSOH the ideal choice for large public buildings where safety of the occupants is imperative, especially hospitals and underground stations. What cables are suitable for single phase residential and other common buildings? 

 

The Prysmian 6242Y is a flat PVC insulated and sheathed low voltage cable commonly known as “twin & earth” which is ideal for small power and lighting applications. It is a two core cable consisting of live and neutral (one brown and one blue) PLUS a bare, uninsulated copper CPC. This cable is ideal for ring, radial, lighting and switching circuits.

 

 

For fire detection and fire alarm systems, it is essential to use fire resistant cables such as FP200 Gold. Prysmian FP200 GOLD is the most common ‘standard’ fire resistant cable solution and features tough Insudite® insulation compliant with E15 to BS EN 50363-5 and a LSOH sheath. It is interesting to note that this fire resistant “twin and earth” cable features two insulated cores: brown and blue, and a tin coated copper conductor as the CPC. It achieves a minimum of 30 minutes survival time in flame and impact, plus an additional requirement for water spray. It is easy to install and terminate.

 

In short, when it comes to low voltage electrical distribution systems, it’s not as simple as just saying live, neutral and earth. Although CPC is commonly insulated with two colours (usually yellow and green) it may or may not be insulated – it depends on the system design. PVC is the most common sheath type as it’s readily available, pliable, easy to manufacture and handle, but for higher conductor temperatures, consider XLPE. When it comes to fire safety, FP200 GOLD features a tough Insudite® insulation which is ideal for fire alarms and fire detection systems.    

 

What sets apart? The electrical industry has counted on us for over a century to deliver products that perform. Our heritage and dedication give you the tools and assurance to get the job done. 

Our experts know the industry inside out. Having manufactured products for over 100 years, our highly skilled and knowledgeable people are well placed to support your contracts, provide technical support and deliver holistic solutions to your business. We are Prysmian – the leaders who assure the stability, safety and supply of our industry. 

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