RESIDENTIAL HOUSE WIRING USING SWITCHES, FUSE, INDICATOR LAMP AND ENERGY METER
Aim:
To study the basic electrical accessories, materials and tools used in wiring.
Electrical Wiring:
Electrical wiring in general refers to insulated conductors used to carry electricity. Materials for wiring interior electrical systems in buildings vary depending on:
- Intended use and amount of power needed of the circuit
- Type of occupancy and size of the building
- National and local regulations
- Environment in which the wiring must operate.
Wiring systems in a single family home or duplex, for example, are simple, with relatively low power requirements, infrequent changes to the building structure and layout, usually with dry, moderate temperature, and non corrosive environmental conditions. In a light commercial environment, more frequent wiring changes can be expected, large apparatus may be installed, and special conditions of heat or moisture may apply.
Types of wiring systems:
1. Cleat wiring
2. Casing capping wiring
3. Metal sheathed wiring
4. Conduit wiring
Rules for Electric Wiring:
As per I.S.I. rules the following point to be noted:
1. A.C. and D.C. circuit should be separated. 3 phases should be indicated with Red, Yellow and Blue colour and the neutral should be indicated with Black colour. In D.C. we should be indicate +ve with Red, -ve with Blue and neutral with black.
2. If the voltage exceeds 250 volt, the Distribution Board and main switches should be provided with danger board symbol.
3. Number of points should not be more than ten and total load in a circuit should not exceed more than 800 watt.
4. Correct size of the conductor should be used, such that the voltage drop should not increase more than 3% of the connected voltage when full load current is following.
5. All distribution boards should be marked as PDB (power distribution board) or LDB (light distribution board).
6. All the accessories should be fixed on the round blocks or board with screws.
7. In the domestic wiring 3-pin plug should be used.
8. All the iron clad appliances, switches, etc., should be earthed
9. All the switches should be connected through live wire.
10. All switchboards should be fixed at a height of 1.l5 meters.
11. All the boards and switches should be fixed on left hand side of the entrance.
THE THREE CONDUCTORS:
In most countries, household power is single-phase electric power, in which a single live conductor brings alternating current into a house, and a neutral returns it to the power supply. Many plugs and sockets include a third contact used for a protective earth ground, which only carries current in case of a fault in the connected equipment.
· Live or Phase
The live conductor (also known as phase, hot or active) carries alternating current from the power source to the equipment.
· Neutral
The neutral conductor returns current from the equipment back to the power source or distribution panel. It is in most (but not all) cases referenced to the earth. Except under fault conditions it does not pose a danger because the voltage between the neutral contact and the earth is close to zero, but is nevertheless treated as live in most installation practices because it can develop a high voltage under fault conditions.
The main danger posed by the neutral is the voltage can rise as high as the voltage on the live conductor if a broken neutral cable in the wiring disconnects the neutral but leaves the live conductor connected.
· Earth/Ground
The earth contact (known as ground in American English) is only intended to carry electric current when connected to equipment that has developed an insulation fault. The earth connection was added to modern plugs because, if a live wire or other component in a device touches the metal casing, anybody touching the device may receive a dangerous electric shock. In many countries devices with metal cases must have the case connected to the earth contact. This reduces but does not eliminate the possibility of the case developing a high voltage relative to the earth and grounded metalwork.
It is a common misconception that the purpose of the earth connection is to take fault currents safely to earth. The primary purpose of the earthing system is to cause a fuse to blow or a breaker to trip to automatically disconnect the power supply to any device or cable which develops a wiring fault. The secondary purpose is to hold all touchable metal in a house to the same voltage to prevent electrical shocks when touching two metal objects at the same time. In addition, some equipment such as surge protectors required an earth connection to function properly because they operate by shorting the excess current to the earth.
Fuse:
In electrical engineering a fuse, short for 'fusible link', is a type of over current protection device. Its essential component is a metal wire or strip that melts when too much current flows. When the metal strip melts, it opens the circuit of which it is a part, and so protects the circuit from excessive current.
A practical fuse was one of the essential features of electrical power distribution system. An early fuse was said to have successfully protected an Edison installation from tampering by a rival gas-lighting concern.
Figure: Fuse Carrier
Fuses (and other over current devices) are an essential part of a power distribution system to prevent fire or damage. When too much current flows through a wire, it may overheat and be damaged or even start a fire. Wiring regulations give the maximum rating of a fuse for protection of a particular circuit. Fuses are selected to allow passage of normal currents, but to quickly interrupt a short circuit or overload condition.
FUSE CHARACTERISTICS:
The speed at which a fuse operates depends on how much current flow through it. Manufacturers of fuses plot a time-current characteristic curve, which shows the time required melting the fuse and the time required to clear the circuit for any given level of overload current.Fuses are often characterized as "fast-blow" or "slow-blow" or "time-delay", according to the time they take to respond to an over current condition. The selection of the characteristic depends on what equipment is being protected. Semiconductor devices may need a fast or ultra fast fuse for protection since semiconductors may have little capacity to withstand even a momentary overload. Fuses applied on motor circuits may have a time-delay characteristic, since the surge of current required at motor start soon decreases and is harmless to wiring and the motor.
Switches:
Bell Push Switch
This type of switch is used to switch ‘on’ a calling bell for a short time. When the switch is released it returns back to its original position.
Single Way Switch
This type of switch is used in electric circuit to control electrical equipment. Only phase wire is connected in the switch terminals. It has two contacts, one fixed contact and one moving contact. The switch is made of porcelain or bakelite.
Two Way Switch
This type of switch is used in electric circuit to control a lamp from two different locations. It has three contacts, two fixed contacts and one moving contact.
Main Switch:
A Main switch is the master control of all the wiring circuit made in the building. Normally Double Pole Iron Clad (DPIC) main system is used in single phase domestic wiring.
Types of Switches
The terms pole and throw are used to describe switch contacts. A pole is a set of contacts that belong to a single circuit. A throw is one of two or more positions that the switch can adopt.
Abbreviation | Expansion of abbreviation | Wiring Name | Description | Symbol |
SPST | Single pole, single throw | One way | A simple on-off switch: The two terminals are either connected together or not connected to anything. | |
SPDT | Single pole, double throw | Two way | A simple changeover switch: C (Common) is connected to L1 or to L2. | |
SPCO | Single pole changeover or Single pole, centre off | Equivalent to SPDT. Some suppliers use SPCO for switches with a stable off position in the centre andSPDT for those without. | ||
DPST | Double pole, single throw | Double pole | Equivalent to two SPSTswitches controlled by a single mechanism | |
DPDT | Double pole, double throw | Equivalent to two SPDTswitches controlled by a single mechanism: A is connected to B and D to E, or A is connected to C and D to F. |
SPECIAL TYPES:
Sockets:
Domestic AC power plugs and sockets are devices that connect the home appliances and portable light fixtures commonly used in homes to the commercial power supply so that AC electric power can flow to them.
Power plugs are male electrical connectors that fit into female electrical sockets. They have contacts that are pins or blades which connect mechanically and electrically to holes or slots in the socket. Plugs usually have a live or hot contact, a neutral contact, and an optional earth or ground contact. Many plugs make no distinction between the live and neutral contacts, and in some cases they have two live contacts. The contacts may be brass, tin or nickel plated.
Power sockets are female electrical connectors that have slots or holes which accept the pins or blades of power plugs inserted into them and deliver electricity to the plugs. Sockets are usually designed to reject any plug which is not built to the same electrical standard. Some sockets have one or more pins that connect to holes in the plug.
An electric meter or energy meter is a device that measures the amount of electrical energy supplied to a residence or business. The most common type is more properly known as a (kilo)watt-hour meter or a joule meter. Utilities record the values measured by these meters to generate aninvoice for the electricity. They may also record other variables including the time when the electricity is used. The most common unit of Measurement on the electricity meter is the kilowatt-hour which is equal to the amount of energy used by a load of one kilowatt over a period of one hour, or 3,600,000 joules.
Electromechanical Meters:
The most common type of electricity meter is the electromechanical induction meter.Fig: Mechanism of electromechanical induction meter. (1) - Voltage coil - many turns of fine wire encased in plastic, connected in parallel with load. (2) - Current coil - three turns of thick wire, connected in series with load. (3) - Stator - concentrates and confines magnetic field. (4) - Aluminium rotor disc. (5) - rotor brake magnets. (6) - spindle with worm gear. (7) - display dials - note that the 1/10, 10 and 1000 dials rotate clockwise while the 1, 100 and 10000 dials rotate counter-clockwise.
The electromechanical induction meter operates by counting the revolutions of an aluminum disc which is made to rotate at a speed proportional to the power. The number of revolutions is thus proportional to the energy usage. It consumes a small amount of power, typically around 2 watts.
The metallic disc is acted upon by two coils. One coil is connected in such a way that it produces a magnetic flux in proportion to the voltage and the other produces a magnetic flux in proportion to the current. This produces eddy currents in the disc and the effect is such that a force is exerted on the disc in proportion to the product of the instantaneous current and voltage. A permanent magnet exerts an opposing force proportional to the speed of rotation of the disc - this act as a brake which causes the disc to stop spinning when power stops is drawn rather than allowing it to spin faster and faster. This causes the disc to rotate at a speed proportional to the power being used.
Indicator Lamp:
An indicator lamp is used to indicate power supply in a board or electric equipment. The red flashing indictor is used in alarm applications. The neon light or light emitting diodes (LED’s) are brighter and are used as indicators. The indicators consume less electrical power. They have longer life (1,00,000 hours of operations) with constant luminous efficiency. Indicator lamps are also used for phase indication in electrical circuit board.
Result:
Thus the basic electrical accessories, materials and tools used in wiring have been used.
FLOURESCENT LAMP WIRING
Aim:
To understand the working principle and to make the necessary connection for the working of a fluorescent lamp.
Materials Required:
1. Frame 4’ – 1 No.
2. Choke/Ballast 40W – 1 No.
3. Starter 40W – 1 No.
4. Holder – 1 PAIR
5. Fluorescent Tube 40 W – 1 No.
6. Flexible Wire 23/0.0076 – 4 Meter.
Theory:
Basics of Light:
Light is a form of energy that can be released by an atom. It is made up of many small particle-like packets that have energy and momentum but no mass. These particles, called light photons, are the most basic units of light.
Atoms release light photons when their electrons become excited. An atom's electrons have different levels of energy, depending on several factors, including their speed and distance from the nucleus. Electrons of different energy levels occupy different orbits.
When an atom gains or loses energy, the change is expressed by the movement of electrons. When something passes energy on to an atom an electron may be temporarily boosted to a higher orbital (farther away from the nucleus). The electron only holds this position for a tiny fraction of a second; almost immediately, it is drawn back toward the nucleus, to its original orbital. As it returns to its original orbital, the electron releases the extra energy in the form of a photon, in some cases a light photon.
The wavelength (colour) of the emitted light depends on how much energy is released, which depends on the particular position of the electron. Consequently, different sorts of atoms will release different sorts of light photons. In other words, the colour of the light is determined by what kind of atom is excited.
Inside the Tube:
The central element in a fluorescent lamp is a sealed glass tube. The tube contains a small bit of mercury and an inert gas, typically argon, kept under very low pressure. The tube also contains a phosphor powder, coated along the inside of the glass. The tube has two electrodes, one at each end, which are wired to an electrical circuit. The electrical circuit is supplied by an alternating current (AC) supply.
When the lamp is turned on, the current flows through the electrical circuit to the electrodes. There is a considerable voltage across the electrodes, so electrons will migrate through the gas from one end of the tube to the other. This energy changes some of the mercury in the tube from a liquid to a gas. As electrons and charged atoms move through the tube, some of them will collide with the gaseous mercury atoms. These collisions excite the atoms, bumping electrons up to higher energy levels. When the electrons return to their original energy level, they release light photons.
The wavelength of a photon is determined by the particular electron arrangement in the atom. The electrons in mercury atoms are arranged in such a way that they mostly release light photons in the ultraviolet wavelength range. Our eyes don't register ultraviolet photons, so this sort of light needs to be converted into visible light to illuminate the lamp. This process is carried out by phosphor powder.
Phosphors are substances that give off white light when they are exposed to ultraviolet light. When a photon (ultraviolet) hits a phosphor atom, one of the phosphor's electrons jumps to a higher energy level and when the electron falls back to its normal level, it releases energy in the form of another photon (white light). In a fluorescent lamp, the emitted light is in the visible spectrum i.e. the phosphor gives off white light that we can see. The colour of the light can be varied by using different combinations of phosphors.
Conventional incandescent light bulbs also emit a good bit of ultraviolet light, but they do not convert any of it to visible light. Consequently, a lot of the energy used to power an incandescent lamp is wasted. A fluorescent lamp puts this invisible light to work, and so is more efficient. Incandescent lamps also lose more energy through heat emission than do fluorescent lamps. Overall, a typical fluorescent lamp is four to six times more efficient than an incandescent lamp.
The entire fluorescent lamp system depends on an electrical current flowing through the gas in the glass tube.
Gas as a Conductor:
Mercury atoms in a fluorescent lamp's glass tube are excited by electrons flowing in an electrical current. This electrical current is something like the current in an ordinary wire, but it passes through gas instead of through a solid. Gas conductors differ from solid conductors in a number of ways.
In a solid conductor, electrical charge is carried by free electrons jumping from atom to atom, from a negatively-charged area to a positively-charged area. As we've seen, electrons always have a negative charge, which means they are always drawn toward positive charges. In a gas, electrical charge is carried by free electrons moving independently of atoms. Current is also carried by ions, atoms that have an electrical charge because they have lost or gained an electron. Like electrons, ions are drawn to oppositely charged areas.
To send a current through gas in a tube, then, a fluorescent light needs to have two things:
- Free electrons and ions
- A difference in charge between the two ends of the tube (a voltage)
Generally, there are few ions and free electrons in a gas, because all of the atoms naturally maintain a neutral charge. Consequently, it is difficult to conduct an electrical current through most gases. When we turn on a fluorescent lamp, the first thing it needs to do is introduce many new free electrons from both electrodes, the next section explains this.
Starting Up the Fluorescent Lamp:
The classic fluorescent lamp design used a special starter switch mechanism to light up the tube.
When the lamp first turns on, the path of least resistance is through the bypass circuit, and across the starter switch. In this circuit, the current passes through the electrodes on both ends of the tube. These electrodes are simple filaments, like the filament in an incandescent light bulb. When the current runs through the bypass circuit, electricity heats up the filaments. This boils off electrons from the metal surface, sending them into the gas tube, ionizing the gas.
At the same time, the electrical current sets off an interesting sequence of events in the starter switch. The conventional starter switch is a small discharge bulb, containing neon or some other gas. The bulb has two electrodes positioned right next to each other. When electricity is initially passed through the bypass circuit, an electrical arc(essentially, a flow of charged particles) jumps between these electrodes to make a connection. This arc lights the bulb in the same way a larger arc lights a fluorescent bulb.
One of the electrodes is a bimetallic strip that bends when it is heated. The small amount of heat from the lit bulb bends the bimetallic strip so it makes contact with the other electrode. With the two electrodes touching each other, the current doesn't need to jump as an arc anymore. Consequently, there are no charged particles flowing through the gas, and the light goes out. Without the heat from the light, the bimetallic strip cools, bending away from the other electrode. This opens the circuit.
Inside the casing of a conventional fluorescent starter there is a small gas discharge lamp.
By the time this happens, the filaments have already ionized the gas in the fluorescent tube, creating an electrically conductive medium. The tube just needs a voltage kick across the electrodes to establish an electrical arc. This kick is provided by the lamp's ballast, a special sort of transformer wired into the circuit.
When the current flows through the bypass circuit, it establishes a magnetic field in part of the ballast. This magnetic field is maintained by the flowing current. When the starter switch is opened, the current is briefly cut off from the ballast. The magnetic field collapses, which creates a sudden jump in current and the ballast releases its stored energy.
The ballast, starter switch and fluorescent bulb are all wired together in a simple circuit.
This surge in current helps build the initial voltage needed to establish the electrical arc through the gas. Instead of flowing through the bypass circuit and jumping across the gap in the starter switch, the electrical current flows through the tube. The free electrons collide with the atoms, knocking loose other electrons, which creates ions. The result is a plasma, a gas composed largely of ions and free electrons, all moving freely. This creates a path for an electrical current.
The impact of flying electrons keeps the two filaments warm, so they continue to emit new electrons into the plasma. As long as there is AC current, and the filaments aren't worn out, current will continue to flow through the tube.
Ballast to Control the Current:
Gases don't conduct electricity in the same way as solids. One major difference between solids and gases is their electrical resistance (the opposition to flowing electricity). In a solid metal conductor such as a wire, resistance is a constant at any given temperature, controlled by the size of the conductor and the nature of the material.
In a gas discharge, such as a fluorescent lamp, current causes resistance to decrease. This is because as more electrons and ions flow through a particular area, they bump into more atoms, which frees up electrons, creating more charged particles. In this way, current will climb on its own in a gas discharge, as long as there is adequate voltage. If the current in a fluorescent light isn't controlled, it can blow out the various electrical components.
A fluorescent lamp's ballast works to control this. The simplest sort of ballast, generally referred to as a magnetic ballast, works something like an inductor. A basic inductor consists of a coil of wire in a circuit, which may be wound around a piece of metal. When we send electrical current through a wire, it generates a magnetic field. Positioning the wire in concentric loops amplifies this field.
This sort of field affects not only objects around the loop, but also the loop itself. Increasing the current in the loop increases the magnetic field, which applies a voltage opposite the flow of current in the wire. In short, a coiled length of wire in a circuit (an inductor) opposes change in the current flowing through it. The transformer elements in a magnetic ballast use this principle to regulate the current in a fluorescent lamp.
Reason for Humming Noise from a Fluorescent Lamp:
Magnetic ballasts modulate electrical current at a relatively low cycle rate, which can cause a noticeable flicker. Magnetic ballasts may also vibrate at a low frequency. This is the source of the audible humming sound people associate with fluorescent lamps.
Electronic Ballast:
Modern ballast designs use advanced electronics to more precisely regulate the current flowing through the electrical circuit. Since they use a higher cycle rate, we don't generally notice a flicker or humming noise coming from electronic ballast.
Latest Advancement:
The problem with the conventional fluorescent lamp explained above, is it takes a few seconds for it to light up. These days, most fluorescent lamps are designed to light up almost instantly. This design works on the same basic principle as the traditional starter lamp, but it doesn't have a starter switch. Instead, the lamp's ballast constantly channels current through both electrodes. This current flow is configured so that there is a charge difference between the two electrodes, establishing a voltage across the tube.
When the fluorescent light is turned on, both electrode filaments heat up very quickly, boiling off electrons, which ionize the gas in the tube. Once the gas is ionized, the voltage difference between the electrodes establishes an electrical arc. The flowing charged particles excite the mercury atoms, triggering the illumination process.
Rapid start and starter switch fluorescent bulbs have two pins that slide against two contact points in an electrical circuit.
An alternative method, used in instant-start fluorescent lamps, is to apply a very high initial voltage to the electrodes. This high voltage creates a corona discharge. Essentially, an excess of electrons on the electrode surface forces some electrons into the gas. These free electrons ionize the gas, and almost instantly the voltage difference between the electrodes establishes an electrical arc.
No matter how the starting mechanism is configured, the end result is the same: a flow of electrical current through an ionized gas.
Circuit Diagram:
Procedure:
1. Fix the tube holders, ballast/choke and starter on the frame.
2. Fix the fluorescent tube in the holders.
3. As per circuit diagram give the connections.
Precautions:
1. There must not be any lose connection.
2. Never give direct supply to lamp (always use fuse and switch in series with the tube).
Result:
The working principle of the fluorescent lamp has been studied and the necessary connections were made to make the fluorescent lamp glow.
STAIRCASE WIRING
Aim:
To control a lamp from two different locations using 2 two – way switches.
Materials Required:
1. Two way switch – 2 no.
2. Lamp – 1 no
3. Wires – 4 meter
4. Holders – 1 no
Theory:
Basics of Switch:
A switch is a device for changing the flow of current in an electrical circuit. A normal switch has two terminals that are either connected or disconnected. If the two terminals are connected the switch is said to be ‘on’ and if the two terminals are disconnected then the switch is said to be ‘off’. When the switch is ‘on’ the current passes from terminal ‘1’ to ‘2’ and when the switch is ‘off’ the current flow is stopped from terminal ‘1’ to ‘2’.
Simple Lamp Wiring with a One-way Switch:
The figure below shows the simplest possible configuration of a lamp wiring using a one-way switch. In this diagram, the black wire is phase. The white wire is neutral. You can see in the figure that the current runs through the switch. The switch simply opens (off) or closes (on) the connection between the two terminals on the switch. When the switch is on, current flows along the black wire through the switch to the light, and then returns to ground through the white wire to complete the circuit.
Figure: Simple lamp wiring using a one-way switch
Two Way Switch:
A two-way switch has three terminals, and the switch connects the first terminal to either the second or the third terminal.
Two Way Wiring With a Two Way Switch:
The following figure shows two no. of two-way switches to control the light.
Assume that, with the switch up, terminals 1 and 2 are connected as shown above. If the switch is down, then terminals 1 and 3 are connected. If you trace through the wires and the switches that in the previous figure, the light is off.
The following figures show the various statuses of switches and the condition of the lamp.
Circuit Diagram:
Procedure:
1. The accessories have to be first placed on the board.
2. Using a poker make markings at suitable spots on the board and drill the spots.
3. Screw the accessories on the board, with necessary precautions
4. Make the connections as per the circuit diagram.
5. Verify the status table.
Status Table:
POSITION OF THE SWITCH | STATUS OF THE LAMP | |||
S1 | S2 | |||
0 | 2 | 2’ | 0’ | ON |
0 | 1 | 2’ | 0’ | OFF |
0 | 1 | 1’ | 0’ | ON |
0 | 2 | 1’ | 0’ | OFF |
Result :
The staircase wiring is performed and the status table has been verified.
