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INTRODUCTION :
Having studied wires and cables it is important to know about electrical controlling, safety, outlet and general accessories.
In an electrical circuit fuse is used as a safety device. Here we are going to discuss about their characteristics and uses. Earthing is also used for safety. It prevents to minimize the risk of shock. The purpose functions and types of earthing are also discussed
An electrical domestic accessories is a basic part used in wiring either for protection & adjustment or for the control of the electrical ciruits or for a combination of these functions.
1. Rating of accessories-
The standard current ratings of the accessories are 6, 16 & 32 ampere. The voltage rating is 240V AC as per B.I.S 1293-1988. Construction of accessories- These accessories should be provided with complete enclosures, which shall afford adequate protection against accidental contact with all live parts.
2. Switches-
A manually operated device for closing & opening a circuit is known as switch.
3. One way switch Single Pole Switch-
Flush, wall mounting or switches is the most popular switches in domestic wiring. The flush (piano) switch must be fixed on a PVC gangbox or on wooden box. The gangboxes ate available in 1gang 2,3, 4, & 6 gang according to no. of switches. Standard gang boxes are designed so that the switch is fixed by screw directly or indirectly (push pull type).One way switch to has current rating 6amperes. These are used for light & fan point rating of power switches is 16 amperes & are used for freeze, mixer, washing machine, geezer, etc. (fig.-S.P. switch)
4. Two-way switch-
This type of switch having 3 terminals. Centre terminal, is known as common terminal ©. Above terminal of common terminal is Upper terminal (u) & below of the common terminal is Lower terminal (L). Two way switch has current rating 6 amperes only. These are used for stair case wiring, godown wiring, hospital wiring. (fig.- Two-way switch)
5. Bellpush-
This type of switch having two terminals with spring loaded push button. When we push it makes the circuit temporarily & attends break position when released. It is used in call bell circuit, current rating is 6 ampere & suitable for 250V only. (fig.- Bellpush)
6. D.P. Switch (Double Pole Switch)-
This switch is consist of double pole switch, fuse, fuse link & neon indicator. These switches are used as main switches to controlled main or branch circuit in domestic installation. They are available in 10ampere, 16ampere & 32 ampere & suitable for 250V only. (fig.- D.P. switch) single pole), two way switch, Bell push, double pole switch ( D.P. switch)
7. Plug Socket
Two pin plug socket having only two pins without earth connection. These are suitable only for double insulated appliances. Current rating of two pin plug socket is 6 ampere & suitable for 250V only. (fig.Plug socket) Three pin plug socket has 3 terminals marked as L( Line), N( Nuetrol) & E( Earth). The L terminal is always on the right hand side, The N terminal of left hand side, & the top is the earth terminal which is larger in diameter & heavy. Dear student you must be connected earth wire to the earth terminal of the socket. This sockets are rated 6 ampere & 16 ampere & suitable for 250V only. Multipin sockets are also available which are suitable for 2 pins & 3 pins having 5 holes in one unit
8. Plug Pin Top
Two pin plug to is used for taking the supply from the socket. It has got two pins of the same size. It is suitable for 6 amperes & 250V only. Three pin plug top also used for taking a supply from the socket . It has 3 pins, two are smaller in size & third one is bigger & longer which is for earth. These are rated as 6A 250V or 16A, 250V. (Fig.- Plug pin top)
9. Ceiling Rose
Two plate ceiling rose is made of PVC & it has two terminals or plates which are separated from each other by a bridge. Each of the terminal plates is provided with a metalic bar & a binding screw on one side through which the circuit wire from the back via the mounting block enters them. The other side of the terminal plate is provided with washer & screw for tap wire connection. It is used for 6A, 250V. (fig.- Ceiling Rose) Three plate ceiling rose also available in market. It has 3 terminals which are separated from each other by a bridge.
10. Adapter
It is used for taking a supply from a lampholder for small appliances. They are made of PVC or bakelite material.
11. Iron Connector
It is used as female connectors to supply current to electric cettels electrical irons, hot plates, heaters, it is made up of bakelite or PVC. The wires are connected with a twin nickel spring. The cable entry has a rubber protection type.
Fuse:
A Fuse is a safety device. It is connected in series with the circuit & protects the electrical apparatus & equipments from damage, when excess current flows. There are several types of Fuses used in electrical field, but the Kitkat type fuse is commonly used in domestic installation. While specifying fuses in general, their type, current capacity & working voltage also should be specified.
A fuse is a safety device used for the purpose of protecting a circuit against excess current. In the event of excessive current, the Fuse element melts & open up the circuit there by protecting it from damage.Electrician Trade Theory 1st Year.
The fuses can interrupt automatically a circuit with an over current in it for a fixed time. They are mainly used to against the short-circuits. They limit the peak value of the fault current.
Placement of fuses -
In electrical installations, the fuses are always connected into the live wires & never into the neutral nor the protective earth line.
Rewirable type fuse -
This type of Fuses are simple in construction & the initial cost as well as the renewal cost is very 10w. The fuse element will melt after approximately 2 minutes when carrying a current rating. Kitkat & Piano type of fuses are the example of rewirable fuses.
Construction of Kitkat & Piano type fuse -
These are mostly use in domestic installation. The fusebse consist of a porceilin or polycarbonate material plastics. Base having silvered heavy brass terminals. The incoming & outgoing positive wire is connected to these terminals. Inside the fuse, carrier two contact terminals are provided. Fuse camer is made up of porceilin or polycarbonate material. It has two brass fuse carrier terminals, having a screw for connecting a fuse element.In modern type fuse, Base contact terminals are made of silver coated brass & fuse carrier also made of tined copper & having a silver fuse.
Fuse element -
Generally Fuse elements are made of tined copper wire.
Function / Working of fuse –
During normal operations fuse element acts as a conductor and it provides complete path of current. When a short circuit occurs the current flowing through fuse increases sharpely. This causes the heating of the fuse element. Fuse element has a low melting point so that it melts at a lower temperature than that of ordinary conductor, when the heat caused by the short circuit current reaches the melting point of the fuse element the element melts & opens the circuit
Fuse Rating –
1. Always use a fuse wire of appriate capacity with respective current.
2. Always use single fuse wire.
3.Never connect multistrand wire as a Fuse.
4. Keep proper length of Fuse element.
5.Connect Fuse wire properly.
Earthing
• Defination -
The earthing of metal parts is achieved by connecting them to an earth conductor which shall be connected by means of an earthing lead to the earth electrode.
• Necessity of Earthing -
The necessity for earthing is to ensure that the metalwork of electrical equipment, other than current carrying parts, cannot have a potential above earth in the event of a fault which might otherwise cause danger of an electric shock. If a fault is developed, causing unearthed metalwork of a piece of electrical equipment; it is charged to a level of dagerous potential. Any person touching the metal & at the same time comes in contact with earth will receive a severe electric shock. Had the metal been effectively earthed, the very low resistance of the circuit would result in a flow of current sufficient to blow the Fuse or to operate the protective device. In an earth metalwork of a piece of electrical equipment becomes a zero potential due to this; a person does not get a shock.
• Plate type earthing :
This method requires the following materials-
1. Copper or G.I. earth plate.
2. Copper or G.I. earth wire.
3. Copper or G.I. nut, bolt & washer.
4. Funnel.
5. G.I. Pipe.
6. Cast iron cover.
7. Salt, Charcoal & water.