Electrical Installation Designs CHAPTER 5 CABLE SELECTION AND

Electrical Installation Designs CHAPTER 5 CABLE SELECTION AND WIRING SYSTEM PPKSE

Electrical Installation Designs CABLE SELECTION AND WIRING SYSTEM Cables are means by which electrical energy is distributed from its source to its point of use. n Defined: length of insulated single conductor or of two or more such conductors each provided with its own insulation which are laid up together. n The insulated conductor or conductors may or not be provided with overall covering for mechanical protection. n A single core cable refers to a cable that has only one insulated conductor with its own cable sheath, and a multi core cable refers to a cable that has multiple cores of insulated conductors within one common sheath. n PPKSE

Electrical Installation Designs CABLE COMPONENTS: CONDUCTOR A conductor may be defined as the conducting portion of a cable, which consists of a single wire or group of wires in contact with each others. n The ability of a material to be a good or bad conductor of electricity depends on the composition of that material, i. e. its resistivity. n Conductors may be divided into two groups: a) solid conductor b) stranded conductor n PPKSE

Electrical Installation Designs CABLE COMPONENTS: CONDUCTOR PPKSE Material Resistivity at 200 C (μΩcm) Silver 1. 58 Copper 1. 72 Gold 2. 36 Aluminium 2. 6 Tungsten 5. 6

Electrical Installation Designs CABLE COMPONENTS: INSULATION Cables are usually a classified according to the type of insulation used. The type of insulation to be used must have the following properties: n It should have a high specific resistance n It should have high dielectric strength n It should be tough and flexible n It should not be hygroscopic, i. e, it should not absorb moisture from air or surroundings. n It should be capable of standing high temperatures without much deterioration. n It should be non inflammable. n It should not be attacked by acids or alkalies. n It should be capable of withstanding high rupturing voltages. PPKSE n

Electrical Installation Designs CABLE COMPONENTS: INSULATION REFER TABLE 4 D 1 A-4 J 4 A (pg 274 – 316) PPKSE

Electrical Installation Designs CABLE COMPONENTS: SHEATHING n n n Sheath - a metallic component over the insulation of a cable. Various metals may be used as the sheath of a cable such as lead, copper, aluminium, bronze, steel, etc. The choice of sheathing material depends on its environmental performance: ambient temperature; flexibility; resistance to abrasion, water, oil and other chemicals; performance under fire conditions; and compatibility with other materials with which a cable is in contact during its operational life. The sheathing material must also be chemically compatible with the other materials used in the cable both during and after processing. While insulations are chosen primarily for their electrical characteristics, sheaths are selected on their physical properties. PPKSE

Electrical Installation Designs CABLE COMPONENTS: SHEATHING n Thus, not all insulations are suitable sheaths. However, in general, insulation and sheath materials are similar: e. g. a thermoplastic sheath protecting thermoplastic insulation. PPKSE

Electrical Installation Designs CABLE COMPONENTS: ARMOURED When cables are not installed in conduit or trunking, they may require armour, most commonly provided by galvanized steel wire (GSW) helically applied in a single layer and known as `SWA' (single-wire armour). n Most types of power cable require mechanical protection and/or an earth conductor to carry fault currents. For most distribution cables this is provided by SWA. Cables with aluminium sheaths seldom require armour. Cables with lead sheaths may be armoured with steel tape, which is cheaper, but SWA is preferred in the UK for the heavier, higher voltage cables for 10 k. V and upwards because it increases corrosion resistance and the longitudinal strength of the cable for installation purposes. Steel tape is normally protected against corrosion by bitumen, but if better corrosion resistance is required, the tape may be galvanised PPKSE n

Electrical Installation Designs Non Armoured Cable Stranded Cable PPKSE Armoured Cable

Electrical Installation Designs PPKSE

Electrical Installation Designs TYPES OF INSTALLATION The final choice of a wiring system must rest with those designing the installation and those ordering the work, but whatever system is employed, good workmanship and the use of proper materials is essential for compliance with the IEE Regulation 130. 2. 1. The necessary skills can be acquired by an electrical trainee who has the correct attitude and dedication to his craft. PPKSE

Electrical Installation Designs TYPES OF INSTALLATION PVC insulated and sheathed wiring systems are used extensively for lighting and socket installations in domestic dwellings. Mechanical damage to the cable caused by impact, abrasion, penetration, compression or tension must be minimised during installation (Regulation 522. 6. 1). PPKSE

Electrical Installation Designs TYPES OF INSTALLATION a) Conduit Installation – Steel conduit/GI or u. PVC b) Trunking Installation c) Tray Installation d) Others – IEE Regulation – Table 4 A 2 page 261 -265 PPKSE