Any device, associated with the wiring and electrical appliance of an installation, such as a switch, a fuse, a plug, a socket-outlet etc. is called the wiring accessory. The cables, flexible cords and various wiring accessories in common use are briefly described below.
Cables:
The cable or wire used in internal wiring is covered with insulation. The conductor is covered with insulation so that it may prevent leakage of current from the conductor and thus minimize the risk of fire and shock.
The wire employed for internal wiring of buildings may be divided into
According to the conductor material used in cables, these may be divided into two classes known as copper cables and aluminum cables.
According to the number of cores, the cable consists of, the cables maybe divided into the classes known as single core cables; twin core cables; three core cables; two core with ECC (earth continuity conductor) cables etc.
According to voltage grading the cables may be divided into two classes:
(i) 250/440 volt cables (ii) 650/1,100 volt cables.
According to type of insulation the cables are of the following types:
1. Vulcanized Indian Rubber (VIR) Cables:
VIR cables are available in 250/440 volt as well as in 650/ 1100 volt grades and are used for general electrical wiring in cleat, casing-capping and conduit wirings.
VIR cable consists of either tinned copper conductor or aluminum conductor covered with a layer of vulcanized Indian rubber insulation. Over the rubber insulation cotton tape sheathed covering is provided with moisture resistant compound bitumen wax or some other insulating material for making the cables moisture proof. The thickness of
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rubber insulation depends upon the voltage grade for which the cable is required.
The copper conductor is tinned to provide protection against corrosion due to presence of traces of sulphur, zinc oxide and other mineral ingredients in the VIR.
2. Tough Rubber Sheathed (TRS) or Cab Type Sheathed (CTS) Cables:
These cables are available in 250/440 volt grades and used in CTS'(or TRS) wiring.
TRS cable is nothing but a vulcanized rubber insulated conductor with an outer protective covering of tough rubber. These cables are water proof, hence can be used in wet conditions. These cables are available as single core, circular twin core, circular three core, flat three cores, twin core with an earth continuity conductor etc. In wiring of a three pin plug separate earth wire may be used, as it will be cheaper in cost and easy in installation.
These cables are cheaper in cost and lighter in weight than lead alloy sheathed cables, described later and have the properties similar to those, of lead sheathed cables.
3. Lead Sheathed Cables:
These cables are also available in 250/440 volt grades and are used for internal wiring where climatic condition is not dry and has a little bit moisture. The lead sheathed cable is a vulcanized rubber insulated conductor covered with a continuous sheath of lead. The lead sheath provides very good protection against the absorption of moisture and sufficient protection against mechanical injury and so can be used without casing or conduit system. It is available as a single core, twin core, flat three core and flat twin core with an earth continuity conductor.
4. Polyvinyl Chloride (PVC) Insulated Cables:
These cables are available in 250/440 and 650/1,100 volt grades and are used in concealed wiring system. In this type of cable conductor is insulated with PVC insulation. Since PVC is harder than rubber so PVC cable does not require cotton tapping and braiding over it for mechanical and moisture protection.
Since the PVC is thermo-plastic insulation, so it is affected at high temperatures and it may soften and flow down. These cables cannot be used for giving connections to the heating appliances, pendant lighting etc. Though the insulation resistance of PVC is lower than that of VIR but its effect is negligible for low and medium voltages below 600 volts,
5. Weather Proof/Cables
These cables are used for outdoor wiring and for power supply or industrial supply.
These cables are either PVC insulated or vulcanized rubber insulated conductors being suitably taped (only in case of vulcanized rubber insulated cable) braided and then compounded with weather resisting material. These cables are available in 250/440 volt and 650/1100 volt grades. These cables are not affected by heat or sun or rain.
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Although TRS cables can be used for outdoor purposes but due to their higher cost, weather proof cables are generally used for outdoor services.
6. Flexible Cords
A cable containing one or more cores, each formed of a group of wires, the diameter of cores and of the wires being very small to afford flexibility, is known as flexible cord.
These are used as connecting wires for such purposes as from ceiling rose to lamp holder, or from socket-outlet to portable apparatus such as radios, fans, lamps, heaters etc. The flexibility of such wires facilitate in handling the appliances and prevent the wires from breakage. The flexible cords used for house hold appliances are available in various pleasing colours, sizes and of various thickness of insulation.
These wires should never be used for fixed wiring.
Switches
A manually operated device used for closing and opening or for changing the connections of a circuit is known as a switch.
The switches used in internal wiring may be classified in various ways. According to the type of base material they are classified as porcelain or bakelite switches. According to colour of base they are either white or black or brown coloured switches. According to operation required, they are classified as one way, two-way, centre off, double pole etc.
switches.
1. One-way Switch
This type of switch consists of two terminals which can be easily seen from the back side of the switch as well, without removing the cover. The switch is always connect* din series with the point (lamp, fan or socket-outlet) to be controlled.
2. Two-way Switch
The switch of this type consists of four terminals, two of them being short-circuited inside the switch. The switch of this type is usually used for the stair-case wiring or circuits where one point is to be controlled from two different places.
3. Two-way Centre off Switch
The switch of this type is just like a two-way switch but having three operations. In the centre it becomes off. Such switches are used when two lamps are to be operated alternately.
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4. Double Pole Switch
This is a combination of two one-way switches, which can be operated simultaneously as ON-OFF terminals of both the switches, are connected together by a handle made of bakelite. Such switches are used as interlinked switches when the load current is less than 5A and supply voltage is under250V.Incaseeither of the voltage or current exceeds the limits mentioned above DPI C switch is used.
5. Push-button Switches
Such switches are used for controlling the electric bells. When the knob is pressed, the circuit is completed and the bell rings and as soon as the knob is left, the circuit becomes open.
6. Table Lamp Switch
This is a small on-off switch which is commonly used in table lamps.
7. Bed Switch
Such switches are used to switch off the table lamps or other lamps while going to sleep or making the lamp on while getting up at night. It is connected in aeries with one of the two flexible wires. The specialty with this switch is that fluorescent material is applied to its knob so that it may glow at night and can easily be seen in darkness. This is a pendant type switch.
The switches are of two types known as surface switches (or tumbler switches) and flush switches (or concealed switches).
i. Tumbler or Surface Switches
Tumbler switches are those which are fixed on the mounting blocks directly fixed on the surface of the wall. Such switches project out the surface of the wall and are in common use. Surface switches are available in round and oblong base.
Round base switches are cheap and in common use. Oblong surface switches are good in appearance, but being costly, are rarely used.
ii. Flush Switches
Flush switches, as obvious from their name, are fixed in flush with the wall and do not project out. These switches are used where high quality performance and appearance are required.
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