2007 Electrical Workshop Manual

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A HAND BOOK

FOR

ELECTRICAL WORKSHOP

Electrical & Electronics Engineering

Amrita School of Engineering

Amrita Vishwa Vidya Peetham

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Department of ECE, 2 | ASE, Amritapuri Campus

Part 1 General

1. Syllabus 2. Lab rules

3. Safety precautions

4. Electrical engineering - An overview 5. Electric power supply system

Part 2 Study of safety devices

1. Importance of safety devices

2. Circuit breakers – MCB, MCCB & RCBO (ELCB) etc 3. Earthing systems

Part 3 House wiring

1. Introduction

2. Systems of distribution of electrical energy 3. Systems of wiring

4. Selection of wiring system 5. Electrical wiring materials

Part 4 Experiments

1. One lamp controlled by one switch 2. Series connection

3. Parallel connection 4. Staircase wiring 5. Hospital wiring 6. Godown wiring

7. Fluorescent lamp wiring

Part 5 Domestic appliances

1. Fan 2. Electric Mixer 3. Electric Iron 4. Refrigerator 5. Air conditioner 6. Electric lamps

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Course Contents

List of study and practical exercises for Electrical Workshop:

Ex. No. 1: Study of power supplies and safety devices

Introduction to electrical supply system

Importance of Safety device in domestic installation

Study of safety devices such as Fuses, MCB, MCCB, ELCB & Earthing.

Ex. No. 2: Electrical wiring practices (House wiring)

Distribution of electrical energy in a domestic electrical installation

Study of wiring tools & accessories Various types of domestic wiring

Exercise in wiring practice

One lamp controlled by one switch Series and parallel connection Staircase wiring

Hospital wiring Godown wiring

Plug socket connection Fluorescent lamp wiring

Ex. No. 3: Study of domestic appliances

Study of different types of electric Lamps – Incandescent lamp, Fluorescent, CFL, Metal halide, Mercury vapour, Sodium vapour and halogen lamp.

Study of home appliances – Mixie, Fan, Refrigerator, Air Conditioner, Iron box, Water heater & Energy meter.

Ex. No. 4:

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List of study and practical exercises for Electronics

Workshop

Ex. No. 1: Familiarization of electronic components and study of measuring devices.

Ohms law verification

Half wave and full wave rectifier

Ex. No. 2: PCB fabrication and soldering practice

Assembling and soldering of Astable multivibrator circuit on a copper clad sheet.

Ex. No. 3: Study of Intel 8085 microprocessor trainer kit concepts

Familiarization of trainer kit

Writing an assembly language program using Intel 8085

Ex. No. 4: Personal computer hardware workshop

General introduction to the PC

Familiarization of main components of a typical desktop computer

PC power supply

Role of a processor in a computer system

Memory

Essential primary components of a motherboard

BIOS

Commonly seen Ports and slots in a general PC

Essential components of a computer network Ex. No. 5: Mini Project

Project – Assemble and solder any electronic circuit and demonstrate its operation.

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General Workshop Rules

All students in the workshop are expected to adhere to the following guidelines.

• The students are supposed to come in proper workshop uniform dress. Wearing shoes in the workshop is compulsory.

• Do not fool around in the lab: Take your lab work seriously and behave appropriately in the laboratory. Be aware of your classmates’ safety as well as your own at all times.

• To successfully complete the experiments in one lab period, you must come prepared to the laboratory. You must read the experiment in advance and answer the pre-lab questions.

• Please treat the instruments with care, as they are very expensive.

• Return the components to the correct bins when you are finished with them. • Before leaving the lab, place the stools under the lab bench.

• Before leaving the lab, turn off the main power switch to the lab bench.

• Keep your work area neat and uncluttered- Have only books and other materials that are needed to conduct the experiment in the laboratory.

• Experiment: The student works with a partner and they both take the data on separate notebooks. The lab instructor will look at the data and sign on your notebook at the end of the experiment.

• Any student missing a lab (not present in the lab) with no proper or reasonable excuse will get a “0” grade on that specific lab and will have his/her final letter grade reduced. Any student missing two labs with no proper excuse will automatically get a failing grade (F).

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Electrical Safety Principles

When planning and performing work on electrical systems and equipment, keep these principles in mind:

Understand the procedure completely before starting the work.

Use good quality footwear/shoes in order to provide maximum resistance.

Never energize any circuit unless you are sure that no one is working on the circuit. Give electric supply to the wiring system only after thorough verification.

Before replacing a blown fuse always remember to put the switch off.

Do not touch switch boards, main switches, holder points etc with wet hands.

Do not use broken switches, sockets or plug.

Use non-conductive tools whenever possible.

Before putting the plug pins in socket put off the plug switch and disconnect the plug by pulling the plug pin and not by pulling cable.

Take utmost care while handling lamps, lamp holders, switches etc, because these materials are brittle.

Never drape electrical cords over heat sources

Before beginning work, tie back long hair, and roll up loose sleeves.

Know the location and how to operate shut-off switches and/or circuit breaker panels. Use these devices to shut off equipment in the event of a fire or electrocution.

Don’t over bend cables when pulling them through a bend in a raceway, often a pressure or squeezing develops causing insulation damage.

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Electrical engineering an over view

Some definitions

Electric current: - Electric currant can be termed as a continuous flow of electrons through a conductor. One ampere is the current produced when a pressure of one volt is applied across a circuit having one ohm resistance.

EMF: - EMF is electro motive force. Potential difference between two points in a circuit is the electrical pressure difference required to drive a current between them. Potential difference may be termed as voltage.

Voltage of a torch battery is 1.5 V and that of automobile battery is 12V. KSEB supply voltage for domestic installation is 240 V.

Electric power (watt):- Electric power, P = Voltage * current * Power factor Unit of electric power is watt (W)

Electric energy:-Unit of electric energy is KWh (Kilo Watt hour) 1 unit energy = 1 KWh KSEB provides one KWh meter at every Installation for measuring consumed energy.

Resistance is the property of a substance due to which it opposes the flow of current through it. Unit of resistance is ohm

Resistance, R = Specific resistance * I / A

Where I is the length of material & A is the area of cross section

Effect of temperature on resistance:-When temperature increases resistance of pure metals and Alloys increases when temperature increases resistance of electrolyte, insulators etc decrease.

Resistance in series:-Consider three resistors connected in series, and then the total resistance of the circuit will be the sum of the three resistors.

Ohms law:-Ohms law states that, the ratio of potential difference between any two points in a conductor to the current flowing between them is constant.

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Study of Electric Power supply

Eelectricity

Electricity is a form of energy. Electricity is the flow of electrons. We get electricity, which is a secondary energy source, from the conversion of other sources of energy, like coal, natural gas, oil, nuclear power, Hydel power and other natural sources, which are called primary sources.

Electric power supply system

AC&DC: DC or direct current is steady current. It never changes its direction, and AC is alternating in nature. AC voltage can be increased or decreased with the help of transformers. By using high voltage AC, we can drastically reduce the transmission losses. AC can be converted into DC easily but reverse is not so easy.

In India state electricity boards are the authorities to generate and distribute electric energy. KSEB generates electric power at a voltage of 11 KV. This power is transmitted by increasing the voltage at different levels as 33 KV, 66KV, 110 KV, 220KVor 400 KV from different substations. At load centers this voltage again stepped down as 11 KV and a feeder network is created. This feeder line energizes the 11KV/415V step down transformer, and from these transformers electric supply can be given to consumers at 240V and 415 V as single phase or three phases.

All domestic and commercial consumers get electric energy from the distribution network of concerned electricity boards. Based on the power requirements of consumers Electricity Boards may give 3-phase connection (for high power) or single phase connection (for low power). In the three phase connections 4 wires are provided, where as in single-phase connection one phase and a neutral connection are provided to the consumers. Phase to neutral voltage in our country is 230 V and phase-to-phase voltage is 400 V of frequency 50 Hz. Most of the appliances work on single-phase supply. There are some motors, which requires three phase supply.

A KWh meter is provided at the consumer end for measuring the electrical energy consumed. KSEB introduces different tariffs for different consumers, as per their connected load and nature of connection.

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Study of safety devices

Importance of safety devices

The safety features are inbuilt with electric power distribution. The current is to flow through the path it is expected to pass and should not take another path through which it is not expected to pass. Conductors made of copper or aluminium are provided across the path for carrying the current and insulators like PVC, paper or rubber are provided across the path through which the current is not expected to flow.

Under abnormal condition there can be failure of insulations and current will flow through the undesired path which can cause damage to equipments and more important the safety of the user. Sometimes the user may inadvertently touch a live conductor and cause electric shock. The circuit may also carry under short circuit condition much more than normal value of the current. The inbuilt safety features will isolate the faulty circuit from the rest of the supply.

The very high currents caused by short circuit situation can cause lots of damage to electrical installation. Protective devices are needed to break short-circuit and overload currents.

Circuit breakers and fuses are protective devices that control the power going to a particular route of wiring. In case of an overload or a short on that circuit, the breaker or fuse trips and automatically shuts off power to that circuit. Fuses are the commonly used protection devices to protect components like wires, transformers electronics circuit modules against overload. The general idea of the fuse is that it "burns fuse link" when current gets higher than it's rating and thus stops the current flowing.

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Types of safety devices

Fuse

Circuit breakers( MCB, MCCB & ELCB)

Earthing.

Basically two types of protections are provided in the power supply system of domestic consumers.

a. Protection from over current.

b. Protection from leakage current due to failure of insulation or inadvertent contact with live conductors by the user.

Over current and Short circuit

One type of situation that wiring needs to be protected against is over current. The electrical wiring is rated for certain maximum current. If you try to pull more current through it, the wiring will heat considerably. When the wiring heats too much, it will cause the melting of cable insulation, cause fire if there is something flammable near cable and even melt the copper conductors in the cable. So protection is needed to guarantee that in case of something tries to pull too much current through mains wiring, this cannot happen for any long time until the fuse blows and stops the current.

Many people are familiar with a "short circuit", which is a type of fault that occurs when two conductors of an electric circuit touch each other. The current flow caused by a short circuit is usually high and rapid and is quickly detected and halted by conventional circuit protective devices, such as fuses or circuit breakers. Ground faults are one type of problem when the insulation fails.

Protection against over current

Every electrical circuit shall be protected against over current by suitable over current devices. These devices could be

a. Miniature Circuit Breaker (MCB) b. Moulded Case Circuit Breaker c. Semi enclosed rewirable fuses

d. High Rupturing Capacity (HRC) fuses

Typical breaking capacities of protective devices are as follows:

HRC fuses - 80 kA MCB - 16 kA Rewirable fuses - 1 to 4 kA

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The use of exposed, substandard, badly wired, wrongly connected or damaged equipment as well as frayed or badly repaired cables reduces the safety of an installation and increases the risk of person receiving an electric shock.

Electrocution is a passage of current through human body, which is dangerous. The flow of current through human body effects vital functions.

a. Breathing b. Heartbeat

A correctly chosen RCCB can detect small currents flowing to earth and reduces the risk of electrocution. Effect of electric current through human body has been well researched and following chart summarizes the results:

Human sensitivity to electricity

500mA Immediate cardiac arrest resulting in death.

70-100mA Cardiac fibillarillation; the heart begins beats at a steady

20-30 mA Muscle contraction can cause respiratory paralysis

10mA Muscle contraction : the person remains stuck, to the conductor

1-10 mA Prickling sensations

However, electrocution should not be viewed in terms of current alone but in terms of contact voltage. A person gets electrocuted by coming in contact with an object that has a different potential from his/her own. The difference in potential causes the current to flow through the body.

The human body has known limits:

- Under normal dry conditions, voltage limit = 50V. - In damp surroundings, voltage limit = 25V.

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FUSES

Fuse is a wire of short length having low melting point which gives protection against excessive current. This excessive current may be due to over load or short circuit. Under normal working condition the current flowing through the circuit is within safe limit. But when some faults such as short circuit occurs the current exceeds the safe limit value, the fuse wire gets heated and melts. This will cause breaking of the circuit. After one fusing operation, fuse wire must be rewired with the same size wire.

This basic guide will help you decide which fuse to fit to ensure the safe use of your household appliances.

• Appliances up to 700 Watts = 3 Amp fuse

• Appliances between 700 and 1000 Watts = 5 Amp fuse

• Appliances over 1000 Watts = 13 Amp fuse COMMON FUSE TYPES

1. Rewirable fuse 2. Cartridge fuse 3. HRC fuse 1. Rewirable fuse:

This is the cheapest method for protecting a circuit from short circuit. Wires of different diameters made of lead and tin are used in the circuit. When large current flows these wires melts and disconnects the faulty circuit from the rest of the supply.

There are different types of fuses. The usual type is the rewirable type in which the fuse wire is carried in a removable fuse link (Fig. a). The fuse link is made of porcelain or other suitable insulating material. The fuse carrier is push-fitted to the fuse base to make the connection through. An advantage of this type is that the blown fuse wire can be replaced with negligible cost. But there is a chance of selecting a wrong size of fuse wire. Another disadvantage with rewirable fuse is that it may sometimes lead to fire hazards, when the fuse wire blows.

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Fig. (a) Rewirable fuse

The semi enclosed rewirable fuses has the following drawbacks:

• It normally melts on 50 % to 100 % excessive overload. The melting current cannot be accurately predicted.

• It takes time to rewire the fuse.

• Standard fuse wire should be always made available. However it is the cheapest mode of protection from short circuit.

2. Cartridge fuse

Cartridge fuse consists of a tube with metal end caps at both ends (Fig. b). The tube is usually made of glass with no filling material. The fuse wire is placed inside the tube, connected between the end caps. Since the tube is made of glass, the fuse element can be easily inspected for breakage. When the fuse is blown, the whole cartridge has to be replaced. The advantages of cartridge fuses are, quick and easy replacement and the fuse rating is marked on the end cap of the cartridge itself. Cartridge fuses are mainly: used in various electrical and electronic equipment.

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3. High Rupturing Capacity Fuse (HRC):

This is a completely enclosed cartridge type of fuse. These fuses are screwed or linked in the circuit. Generally it is used in the high power circuits. High Rupturing Capacity (HRC) fuse consists of a porcelain tube! with metal end caps and fixing tags (Fig. c). The fuse element is held inside the tube between the end caps and the tube is filled with silica sand or granulated quartz. When the fuse element blows, the silica inside the tube prevent the formation of an arc, and thus avoids the possibility of fire hazards. HRC fuse links are available in a range of 10A to 800A.

The HRC fuse has the following advantages:

• It is very reliable.

• It has an enclosed fuse wire, therefore no chance its arc doing any damage to the surroundings.

• It has low temperature rise at rated load. • Maintenance free.

The drawbacks are:

• It is costly.

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Circuit breakers

MCB and ELCB

MCB is miniature circuit breaker. It is automatic in action. When excessive current passes through the circuit, handle of MCB will moves down and thus trips the circuit. After one such an operation we can manually reset the supply by solving the fault in that circuit. Thus rewiring fault size fuse wire in the case of fuse can be avoided by using MCBs.

ELCB is earth leakage circuit breaker. It protects the circuit from any leakage of current. It protects the circuit from lightning and thunder.

Miniature Circuit Breaker (MCB)

Miniature circuit breakers are compact devices used in distribution boards for protection against overload and short circuit. The overload protection is achieved by a thermal trip mechanism using a bimetallic strip. An electromagnetic trip mechanism is also incorporated for instantaneous tripping in the event of a short circuit.

When there is a sudden increase in current due to a short circuit, the circuit should open immediately, but the bimetallic strip does not respond quickly. In this case, the solenoid attracts the plunger and thus triggers the trip mechanism. After clearing the fault, the MCB can be switched on manually.

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Fig. below shows the current path in a typical miniature circuit breaker when it is in the 'on' position. The current passes through a solenoid coil and a bimetallic strip. When an overload condition persists for a few seconds, the bimetallic strip bends and triggers the trip mechanism.

The principle of operation of an MCB is based on the following two principles.

a. Thermal operation b. Magnetic operation

a. Thermal operation

In thermal operation, the extra heat produced by the high current warms the bimetal strip. This results in bending the bimetallic strip and trips the operating contacts. The thermal operation is slow. Hence, it is not suitable for speedy disconnection required to clear fault currents. However, it is ideal for operation in the event of small but prolonged overload currents. Thus, in general the thermal operation is suitable for opening the circuit in the event of excessive current due to the overloaded machines.

b. Magnetic operation

The magnetic operation, on the other hand is suitable for protection against high short circuit currents. This magnetic operation is due to the magnetic field set up by a coil carrying the current, which attracts an iron part to trip the breaker when the

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current becomes large enough. The magnetic operation is very fast and is used for braking fault currents.

In most cases of MCB' s, both types are provided so that overload currents and short circuit currents are handled with the same degree. It should however be remembered that the mechanical operation of opening the contacts takes a definite minimum time, typically 20ms, so that there can never be the possibility of truly instantaneous operation.

In many installations, MCBs are preferred over fuses mainly because there is no need of rewiring the fuse wire or replacing the cartridge. MCBs are available in a range of 0.5A to 63A normal operating current and for the entire range, the, physical dimensions are almost identical.

The major advantages of MCB’s are

• Instantaneous opening of the contact on short circuit faults

• Can be designed to operate even for very small overload currents • They can be quickly reset by hand

• They cannot be reclosed if fault persist

• In many cases they preferred over fuses as there is no need to rewire it.

Earth Leakage Circuit Breaker

The earth leakage circuit breaker (ELCB) is a protective device, which will automatically trip, when there is an earth leakage within the installation. It is also known as residual current circuit breaker (RCCB). It works on the current balance principle. The main part is a core consisting of three windings. Here one winding carries the phase current, the other winding carries the neutral current and the third winding to the tripping circuit. Under normal operating conditions the net flux in the core is zero as such no emf induced in the trip coil. However, when earth fault occurs, the phase and neutral current varies, the net flux in the core will be different and as such, emf is induced in the trip coil and it is energized. It then opens the circuit. The functioning of the ELCB can be checked using a switch.

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RCD - Residual Current Device. This is a generic term for the entire range of RCDs.

RCCB - Residual Current Circuit Breaker. This is basically a mechanical switch with an RCD function added to it. Its sole function is to provide protection against earth fault currents.

RCBO- Residual Current Breaker with Over current Protection. This is basically an over current circuit breaker (such as an MCB) with an RCD function added to it. It has two functions,

Types of RCD

RCDs can be divided into two categories based on the means by which they detect and respond to earth fault currents. The two types are Voltage Independent (VI) and Voltage Dependent (VD). These are sometimes also referred to as electromechanical and electronic types respectively. The VI type uses the output energy from the CT to activate a relay which in turn activates a tripping mechanism causing the RCD to trip. The VD type uses electronic circuitry to detect the earth fault current and to activate a tripping mechanism causing the RCD to trip. The VI device derives its operating energy from the earth fault current whereas the VD device derives its operating energy from the mains supply.

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Earthing

What is earthing /grounding?

Earthing or grounding is the term used for electrical connection to the general mass of earth. Equipment or a system is said to be 'earthed' when it is effectively connected to the ground with a conducting object. Earthing provides protection to personal and equipment by ensuring operation of the protective gear and isolation of faulty circuit during:

• Insulation failure • Accidental contact • Lightning strike

Importance of earthing

Earthing is necessary for proper functioning of certain equipments. Earthing is done also for preventing the operating personal from hazardous shocks caused by the damage of the heating appliances. Consider an electric heater connected to the supply using two-pin plug and socket. If by some chance the heating element comes in contact with the metallic body of the heater, the body of the heater being a conducting material will be at the same potential as the heating coil. If a person comes and touches the body of the heater, current will flow through his body, which will result in an electric shock.

To avoid unnecessary accident, it is recommended that electric heater be connected to a 3-pin socket using a 3-core cable. (Note: To see a three-core cable, open a plug of an electric iron. There will be three wires, red, blue and green. The green wire connected to the body of the iron is the earth wire) In this case the body of the electric heater is connected to the green wire of the cable, which is connected to the earth through the earth terminal. Besides the body of the electric heater, bodies of hot plates, kettles, toasters, heaters, ovens, refrigerators, air conditioners, coolers, electric irons etc could be earthed using three pin plugs. The resistance of the path to the earth terminal through the earth wire is very low. Hence, even if the heating element comes in contact with the metallic body and a human being comes in contact with the metallic body, major part of the current will flow only through the earth wire (usually the green wire in a 3 core cable). Moreover because of the low resistance path, a large current will flow through the phase wire and the fuse will blow off. For large current to flow, earth resistance should be low. To achieve this proper earthing has to be done.

Earthing is classified as:

a. System earthing

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System earthing: It is the earthing of neutrals of generating stations and substations. It is employed to limit the voltage of live conductors with respect to potential of general mass of earth. This is necessary to prevent failure of insulation.

Equipment earthing: Is earthing of non current carrying metal parts of electrical equipments. As per Rules 33 and 61 of Indian Electricity Rule 1956 non-current carrying metal parts must be earthed with two separate and distinct earth continuity conductors to an efficient earth electrode. However equipments with double insulation need not be earthed.

Some Definitions:

Earthing: A tower/ equipments connecting to the general mass of earth by means of an electrical conductor.

Earth Electrode: Connection to earth is achieved by electrically connecting a metal plate, rod or other conductors or an array of conductors to the general mass of earth. This metal plate or rod or conductor is called as "Earth electrode".

Earth lead: The conductor by which connection to earth is made.

Earth loop impedance: The total resistance of earth path including that of conductors, earth wire, earth leads and earth electrodes at consumer end and substation end.

Factors affecting the value of earth electrode resistance

• Electrode material. • Electrode size.

• Material and size of earth wire. • Moisture content of soil.

• Depth of electrode of underground.

• Quantity of dust and charcoal in earth pit.

Earth resistance consists of following components

• Resistance of metal electrode

• Contact resistance between electrode and soil • Resistance of soil away from electrode surface.

The resistance decreases with the presence of moisture and salt in soil. To increase the effectiveness of earth, the total earth resistance should be reduced. Efforts should be made to reduce the resistance contributed by each of above three components.

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Earth Electrodes

Earth electrodes can be following shapes

• Driven Rods or pipes • Horizontal Wires • Four Pointed Stars • Conductive Plates

o Round Vertical Plates o Square Vertical Plates • Buried Radial Wires

• Spheres made of metal • Water Pipes

Water pipe as earth electrode

As water pipes exist extensively and these are most of the time embedded in earth, they can make a good earth electrode. Such earthing is not objectionable with alternating currents. But with direct currents, the flow of fault currents in pipes produces electrolysis and results in heavy corrosion of pipes. This electrolysis process makes the water also harmful to certain extent. If water pipes are proposed to be used as earth electrode, then only main water supply pipe should be used as an electrode. The water supply main pipe should have metal-to-metal joints between its segments. A perfect electrical connection should be made between water pipe & earth conductor. Pipe should be cleaned thoroughly with emery paper. Earth conductor also should be cleaned thoroughly. The cleaned conductor should be wrapped 4 to 5 times and ends clamped by nuts & bolts. The earth resistance achieved by such an arrangement is usually a fraction of an ohm. Low resistance of such system is due to long length of water pipe and the fact that it is mostly embedded below earth. This method is mostly used for grounding in telephone services. Electrodes should be made of a metal, which has a high conductivity. Normally copper is used. The size of the electrode should be such, that it is able to conduct the expected value of stray equipments. For example a 3 phase star wound generator must have its neutral point at earth potential.

The salts commonly used for chemical treatment of soil are

• Sodium Chloride • Calcium Chloride • Sodium Nitrate • Magnesium Sulphate

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Other factors, which affect the soil resistivity, are

1. Temperature of soil: the resistivity increases when temperature falls below the freezing point. If the temperature falls from 20degrees C to O degree C, soil resistivity goes up from 7200-ohm cm to 14000-ohm cm.

2. Moisture Content of Soil: Small changes in moisture content seriously affect the resistivity. For example if the moisture content changes from 25% to 30%, soil resistivity drops from 250000-ohm cms to 6400-ohm cm. It is important that earth electrodes should be in contact with moist soil. It should be ensured that the electrodes are deep in soil and if possible below the permanent water level.

3. Mechanical Composition of soil: finer the grading, lower the resistance. Methods of placing earth electrodes in soil

1. Pipe Earthing:

Fig. E (1) Cross section of pipe earthing

Pipe earthing is done by permanently placing a pipe in wet ground. The pipe can be made of steel, galvanized iron or cast iron. Usually GI pipes having a length of 2.5m and an internal diameter of 38mm are used. The pipe should not be painted or coated with any non-conducting material.

Fig. E (1) shows an illustration of a typical pipe electrode. The pipe should be placed atleast 1.25m below the ground level and it should be surrounded by alternate layers of charcoal and salt for a distance of around 15 cm. This is to maintain the moisture

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level and to obtain lower earth resistance. The earth lead of sufficient gauge should be firmly connected to the electrode and it should be carried in a Gl pipe at a depth of 60cm below the ground level. A funnel with a wire mesh should be provided to pour water into the sump. Three or four bucket of water should be poured in a few days particularly during summer season. This is to keep the surroundings of the electrode permanently moist.

2. Plate earthing

Fig. E (2) Plate earthing

A typical illustration of plate earthing is shown in Fig. E (2). The plate electrode should have a minimum dimension of 600x600x3.15mm for copper plate or 600x600x6.3mm for Gl plates. The plate electrode should be placed atleast 1.5m below the ground level. The earth conductor is to be securely connected to the plate by means of bolts and nuts. The bolts and nuts should be of the same material as that of the plate. The earth conductor should be carried in a Gl pipe buried 60 cm below the ground level. The plate electrode should be surrounded by a layer of charcoal to reduce the earth resistance. A separate Gl pipe with funnel and wire mesh attached is provided to pour water into the sump.

3. Strip earthing

For all places having a rocky soil bed, this type of earthing is suitable. On this system, wires or strips made of GI of size 25 mm x 4 mm or made of copper of size 25 mm x 1.6 mm are embedded 0.5 m, below the soil in the form of a network. The length should not be less than 1.5 m as per ISI specification. Detail are given in figure below.

Ground level Cast iron cover Wire mesh Cement concrete 19mm dlaGI pipe Charcoal

600x600x6.3mm Gl plate

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Effect of Soil Properties in Earthing

While it is not possible to change the fundamental nature /properties of soil at a given location, but local variations of soil conditions do occur even in a small area. When a location for making earthing pit has to be selected, preference should be given to location, which is likely to give minimum electrical resistance. In the list below, soils have been arranged in ascending order with regard to their electrical resistance.

• Wet marshy lands, or lands containing ashes (Avg Resistivity 2400 ohm cms) • Clay, loamy soil, arable land clay

• Clay & loam mixed with varying proportion of gravel & sand (Avg Resistivity 15,800 ohm cms)

• Damp & wet sands • Dry sand

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House Wiring

Introduction

A network of wires connecting various accessories for distribution of electrical energy from the supplier’s meter board to the numerous electrical energy consuming devices such as lamps, fans and other domestic appliances through controlling and safety devices is known as wiring system.

The supplier’s service cable feeding an installation terminates in what is usually called the service fuses. In an ordinary house the service fuse is called as service cutout. Such cutouts including service meters remain the property of the supplier and represent the furthest point of the supplier responsibility. The point at which the consumer's wiring is connected into cutout is known as point of commencement of supply or consumer's terminals. From consumer terminals onwards the supply cables are entirely under the control of consumer's and so laid out as per his selection. A typical house wiring circuit is shown in fig. a

fig (a)

Systems of distribution of electrical energy

Since as per recommendations of ISI the maximum number of points of lights, fans and socket-outlet that can be connected in one circuit is 10 and the maximum load that can be connected in such a circuit is 800 watts, hence in case more load or more points are required to be connected to the supply system, then it is to be done by having more than one circuit.

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Distribution Board System

In distribution board system, which is most commonly adopted for distribution of electrical energy in a building, the fuses of various circuits are grouped together on a distribution board, some times simply known as fuse board.

The two copper strips, known as bus-bars, fixed in a distribution board of hard wood or metal case are connected to the supply main through a linked switch so that the installation can be switched off as a whole from both the poles of supply if required. A fuse is inserted in the + ve or phase pole of each circuit so that each circuit is connected up through its own particular fuse.

In large buildings, however, if only one distribution board were used, some of the points would be at a considerable distance from it and in such cases it is advisable to employ sub-distribution boards either to save cable or to prevent too great voltage drop at the more distant points (lamps or fans or other appliances). In such cases main distribution board controls the circuit to each sub-distribution board from which the sub-circuits are taken, as shown in fig. a

The number of circuits and sub-circuits are decided as per number of points to be wired and load to be connected to the supply system. For determination of load of an installation the following ratings maybe assumed unless the values are known or specified.

a) Fluorescent lamps — 40 watts.

b) Incandescent lamps, fans, and socket outlets — 60 watts. c) Power socket-outlets — 1,000 watts.

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The Tree System

Another system of distribution of electrical energy in a building is the tree system. In this system smaller branches are taken from the main branch, as shown in fig. b and the wiring system resembles a tree. As each branch is taken off, a fuse is inserted. This system used to be employed in early days. Now-a-days it is no more adopted due to the following draw-backs in this system.

a) The voltage across all the lamps does not remain the same. The lamps in the last branch will have least voltage across them on account of voltage drop in leads,

b) A number of joints are involved in each circuit. c) Fuses are scattered.

d) In case of occurrence of fault all the joints have to be located and if some of these joints are concealed beneath floors or roof spaces, a lot of

difficulties are to be faced. Sometimes a number of such joints are required to be opened for testing purposes, so damage is caused to installation, conductors and building.

Methods of wiring

There are two methods of wiring known as

a) joint box system (or Tee system) and b) Loop-in system

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1. Joint Box or Tee System:

In joint box system the connections to the lamps are made through joints made in joint boxes by means of suitable connectors or joint cutouts. In this method though there is a saving in the quantity of wire or cable required but the same is offset by the extra cost of joint boxes. The other disadvantage of connections is that the number of T-connections made in a wiring system results in weakness if not properly made. Now-a-days the use of this system is limited to temporary installations only, as its cost is low.

2. Loop- in- system:

This system is universally employed for connections of various lamps or other appliances in parallel. In this system when a connection is required at a light or switch, the feed conductor is looped-in by bringing it direct to the terminal and then carrying it forward again to the next point to be fed, as shown in fig. d. The switch and light feeds are carried round the circuit in a series of loops from one point to another until the last point on the circuit is reached.

The phase or line conductors are looped either in switch board or box and neutral conductors are looped either in switch board or from light or fan. Line or phase should never be looped from light or fan.

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The advantages and disadvantages of loop-in system are as follows;

Advantages

a) Joint boxes are not required.

b) In loop-in system no joint is concealed beneath floor or in roof spaces. As they are made only at outlets so they are accessible for inspection and opening out merely by removing the fitments

concerned. Hence fault location is easy.

Disadvantages:

a) Length of wire or cable required is more and voltage drops and copper losses are, therefore, more.

b) Looping-in switches and lamp holders is usually difficult. SYSTEMS OF WIRING

The types of internal wiring usually employed in our country are:

1. Cleat wiring:

In this system of internal wiring the cables used are either VIR or PVC type. The cables are held by porcelain cleats about 6 mm above the walls or ceiling. The cleats are made in two halves, one base and the other cap. The base is grooved to accommodate the cables and the cap is put over it and whole of it is then screwed on wooden plugs (gutties) previously cemented into the wall or ceiling. Thus the cables are firmly griped between the two halves of the cleats and secured to the supporting wall or ceiling. The cleats used are of different sizes and different types in order to accommodate cables of various sizes and different numbers of cables respectively. The cleats are of three types—one groove, two grooves and three grooves to accommodate one, two, and three cables respectively.

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Advantages:

a) It is the cheapest system of internal wiring. b) Its installation and dismantlement is easy and quick. c) Material is recoverable after dismantlement.

d) Inspection, alterations and additions can be easily made. e) Skill required is little.

Disadvantages:

a) It is not good looking.

b) It is quite temporary and perishes quickly. c) The wires are exposed to mechanical injury.

d) The insulation catches dampness from the atmosphere and common salt like substance appears on the insulation which lowers the insulation resistance and Causes leakage. Hence this system of wiring cannot be used in damp places.

e) Oil and smoke are injurious to VIR insulation. Fields of Application:

The wiring of this type is very suitable for temporary installations in dry places. This is also acceptable where appearance is not so important and cheapness is the main consideration. This system is not suitable for use in domestic premises.

2. Wooden Casing and Capping Wiring:

The cable used in this type of wiring is either VIR or PVC or any other approved insulated cables. The cables are carried through the wooden casing enclosures. The casing consists of V-shaped grooves (usually two to hold the cables of opposite polarity in different groves) and is covered at the top by means of rectangular strip of wood, known as capping, of same width as that of casing. The capping is screwed to the casing by means of wooden screws fixed at every 15 cm on the centre fillet. To protect the casing against white ants first class seasoned teak wood, varnished by shellac varnish is employed. Two or three cables of same polarity (either all phases or all neutrals) may be run in one groove and in no case the cables of opposite polarity should be run in the same groove. The casing ia usually placed 3.2 mm apart from the wall or ceiling by means of porcelain distance pieces of thickness not less than 6.5 mm in order to keep the casing dry at the back.

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3. CTS or TRS Wiring.

In this type of wiring the cables used may be single core, twin core or three core TRS cables with a circular oval shape. Usually single core cables are preferred. TRS cables are sufficiently chemical proof, water proof, steam proof but are slightly affected by lubricating oils. TRS eaoles are run on well seasoned, perfectly straight and well varnished (on all four sides) teak wood batten of thickness 10 mm at least. The width of the batten depends upon the number and size of cables to be carried by it. The battens are available in width of 13,19,25,31,38,44,50,56,63,69 and 75 mm. The wooden battens are secured to the walls or ceiling by flat head wood screws to wood or other approved plugs at an interval not exceeding 75 cm. The cables are held on the wooden batten by means of tinned brass link clips already fixed on the batten with brass pins and spaced at an interval of 10 cm in case of horizontal runs and 15 cm in case of vertical runs. The wiring after erection is neatly painted with two coats of oil-less non-cracking paint as specified in IS 732 and so on.

Advantages

a) Its installation is easy and quick and saving in labor largely compensate for the extra cost of the cable.

b) Its life is long.

c) Within certain limits it is fire proof.

d) It can withstand the action of most chemicals such as acids and alkalies. e) It is cheaper than other types of wiring except cleat wiring.

f) If the job is carried out with proper attention, it gives a nice appearance.

Disadvantages

a) Good workmanship is required to make a sound job in TRS wiring. b) This type of wiring cannot be recommended for use in situations open to sun or rain unless preventive steps are taken to preserve the

insulation of cables. Fields of Application

The TRS wiring is suitable for low voltage installations and is extensively used for lighting purposes everywhere i.e. in domestic, commercial or industrial buildings except workshop where it is liable to mechanical injury.

This type of wiring is suitable in situations where acids and alkalies are likely to be present.

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4. Lead Sheathed Wiring

This type of wiring employs conductors insulated with VIR and is covered with an outer sheath of lead aluminum alloy containing about 95% lead. This metal sheath gives protection to the cable from mechanical injury, dampness and atmospheric corrosion. The whole lead covering is made electrically continuous and is connected to earth at the point of entry to protect against electrolytic action due to leaking current and to provide safety against the sheath becoming a live. The cables are run on wooden batten and fixed by means of link clips as in TRS wiring. The great part of the cable employed is flat twin (the cable having two insulated conductors side by side covered with red and black tape respectively and under one flat covering of lead alloy). Three-core flat type cable is also used in certain cases as well as single core cables under a circular sheath of lead alloy.

Advantages

a) It provides protection against mechanical injury better than provided by TRS wiring.

b) It is easy to fix and looks nice as it can be run in building without damaging decoration and can be painted to suit colour scheme of the surroundings.

c) Its life is long if proper earth continuity is maintained throughout. d) It can be use din damp situations provided protection against moisture effect on the ends of the cable is given.

e) It can be used in situations exposed to rain and sun provided no joint is exposed.

Disadvantages

a) It is costlier than TRS wiring.

b) It is not suitable for places where chemical corrosion may occur.

c) In case of damage to insulation the metal sheath becomes alive and gives shock, so as to provide safety against electrical shock it is necessary that the sheath is properly earthed and an earth wire is run side by side with it and all pieces are properly bounded or joined together so that not a single cover is left unearthed.

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Fields of Application

This wiring system is suitable for low voltage (up to 250 volts) installations. It may be used in places exposed to sun and rain provided no joint is exposed. It may also be used in damp places with a suitable protective covering. It should not be used in places where chemical corrosion may occur.. This type of wiring is not very common in use these days except for some small installations and distribution boards etc.

5. Conduit Wiring

In this system of wiring steel tubes, known as conduits, are installed on the surface of walls by means of saddles or pipe hooks or buried under plaster and VIR or PVC cables are drawn into afterwards by means of a GI wire of size of about 18 SWG. In damp situations the conduits can be spaced from the walls by means of small wooden blocks fixed below the pipes at regular intervals. In order to facilitate drawing of wires numbers of inspection fittings are provided along its length. The conduits should be electrically and mechanically continuous and connected to earth at some suitable point. The conduits used for this purpose are of two types namely (i) light gauge (or split type) conduit and heavy gauge (or screwed type) conduit. Light gauge or split conduit with a seam along its length is used for cheap work. It is not water tight or even damp proof and is not permitted on medium voltage (i.e. on voltages higher than 250V). Screwed conduit (solid drawn or with welded seam) is used for all medium voltage (250 V or 600 V) circuits and in places where good mechanical protection and absolute protection from moisture is desired. In general the finish of the conduit is black stove-enamelled, there being a smooth coating of enamel both on the inside and outside surface of the tube. Galvanized conduit is also employed, especially in damp situation when the conduit is on the surface but under ordinary conditions buried in walls it offers little, if any, advantage over good enamelled conduits.

Advantages

a) It provides protection against mechanical damage.

b) It provides complete protection against fire due to short-circuits etc. c) The whole system is water proof.

d) Replacement and alteration of defective wiring is easy. e) Its life is long if the work is properly executed.

f) It is shock proof also if earthing and bonding is properly done. Disadvantages

a) It is very costly system of wiring.

b) Its erection is not so easy and requires time.

c) Experienced and highly skilled labour is required for carrying out the job. d) Internal condensation of moisture may cause damage to the insulation

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Fields of Application

As this system of wiring provides protection against fire, mechanical damage and dampness so this is the only approved system of wiring for:

a) Places where considerable dust or puff is present such as in textile mills, saw mills, flour mills etc.

b) Damp situations.

c) In workshops for lighting and motor wiring.

d) Places, where there is a possibility of fire hazards such as in oil mills, varnish factories etc.

e) Places, where important documents are kept such as a record room.

f) Residential and public buildings, where the appearance is the prime thing. The recessed type conduit wiring is preferred for residential and public buildings.

CHOICE OF WIRING

The following factors should be considered before selecting a particular type of wiring. a. Safety: The first and foremost consideration is safety to a person using electricity

against leakage or shock. Where there is a possibility of fire hazard, conduit wiring is used.

b. Mechanical Protection: The wiring must be protected from mechanical damage during use.

c. Permanency: The wiring must not deteriorate unduly by action of weather, fumes, dampness etc.

d. Appearance: The wiring should he good looking. e. Durability: The wiring must be durable.

f. Accessibility: In wiring system there should be facilities for extension, renewal or alterations.

g. Initial Cost: The wiring selected should suit the pocket of the owner of the building.

h. Maintenance Cost: The wiring should have, as far as possible, the lowest maintenance cost.

The other factors, in addition to above, to be kept in view while making the choice of wiring is load voltage to be employed, type of building etc.

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Tools used in Electric Wiring

Some of the most commonly used tools are described below:

Sl # Tool Size Uses

1. Screw Driver(Smaller size screw driver is called Connector

10,15,20,30 cms Used for loosing or tightening or to keep screws in position.

2. Combination Pliers 15,20,25 cms For holding, twisting or cutting wires.

3. Round Nose Pliers or Flat Nose Pliers

10 cms For holding, twisting or joining the wires at narrow places.

4. Side Cutting Pliers(side cutter)

20 cms For cutting wire at narrow or ordinary places and for removing insulation.

5. Electrician Knife 10 cms It has two blades, one for removing insulation of wires and other for cleaning the wires.

6. Electric Soldering iron 25,40,65,125 W

To solder the joints of wires and winding wires.

7. Cross peen Hammer !/4 kg to 2 kg Used for fixing clip and making gitties hole in wall.

8. Ball peen Hammer '/* kg to 2 kg Best suited for chipping on teak wood batten, and riveting purpose in sheet metal works.

9. Tenon saw or Hand saw

30.5 cm & 40.5 cm

Used for cutting wooden boards, block casings etc.

10. Poker 10, 15 cm Used for making pilot holes for fixing wood screw.

11. Hand drill 3,6,12mm Used for making holes in wooden blocks and boards.

12. Hacksaw 16,20,25,30 cms

Used for cutting conduit G.I. pipes or mild steel.

13. Measuring Tape 10,20mm Used for measuring the dimension of the wiring. It is made of steel or cotton cloth. 14. Wire Stripper & Cutter Used for removing insulation of PVC wires

and available with adjustable 22 SWG and onwards.

15. Files (Flat, round half) 3" to 4" To smooth the surface or corners of any iron board etc.

16. Crimping Tool 1.5,2.5,6mm As soldering on Aluminium is difficult, this plier is used to crimp the joint or lugs.

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STUDY OF WIRING ACCESSORIES

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 different groups according to

a. Conductor used

b. number of cores used c. voltage grading and d. type of insulation used

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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Ceiling Rose

The ceiling rose is used to connect the pendant lamps, fans or fluorescent tubes to the installation through flexible or silk covered wires. These are not used on a circuit, the voltage of which normally exceeds 250 volts.

Fig26.8 shows a modern form of moulded ceiling rose which includes the earth terminal and a shrouded terminal for looping in live wire.

Socket-Outlets

The socket-outlets are used to supply electrical connections whenever required for electrical appliances such as radios, table fans, table lamps, iron, stoves etc. Socket-outlets are of two types— two pin type and three pin type. Two pin socket-Socket-outlets have become obsolete now-a-days. The three pin type socket-outlet has got three hollow terminals in which three pin plugs can easily be inserted but not loosely. Two holes being of same size, are meant for making connections to the flexible wire of the appliance and the third hole, which is bigger comparatively, is meant for earth connections. Thus three holes or sleeves are for live, neutral and earth connections. The three pin socket-outlets are also of two types:

(i) 5 A for table fans, table lamps, radios etc, and (ii) 15 A for power circuits as heater, stove, iron etc.

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Plugs

Plugs are used to take the supply from the socket-outlets for electrical appliances such as table lamp, table fan, heater etc. Similar to socket-outlets plugs are also of two types namely two pin and three pin. Two pin type plugs have become obsolete now-a-days. Three pin type plugs consist of three pins usually made from brass. To the two pins which are thin and of same size, flexible wires are connected and then covered up. To the third pin, which is thicker comparatively, earth wire from the electrical appliance is connected. Similar to 3 pin-socket outlets 3 pin plugs are also of two types—5 A and 15 A. (see fig. 26.10)

Lamp Holders

As the name indicates the function of lamp holder is to support the lamp and also to connect it electrically. These are designed for quick removal and replacement of the lamp. Lamp holders are of many types. A few will be described here.

Lamp-holders may be either of brass or bakelite type with porcelain interior. Brass holders are more durable but may give shock if connections are poor. Though bakelite holders are not durable, but do not give shock.

The following are the different types of lamp holders

1. Batten Holders

Such lamp holders are used where the lamp is to he fitted to the roof or to the wall i.e. it is directly fitted either to batten or to wooden boards. Such lamp holders are bayonet type i.e. in such a lamp holder the lamp is forced in. turned slightly and left in position.

2007 Electrical Workshop Manual

A HAND BOOK

FOR

ELECTRICAL WORKSHOP

Electrical & Electronics Engineering

Amrita School of Engineering

Amrita Vishwa Vidya Peetham

CONTENTS

Part 1 General

Part 2 Study of safety devices

Part 3 House wiring

Part 4 Experiments

Part 5 Domestic appliances

Course Contents

List of study and practical exercises for Electrical Workshop:

List of study and practical exercises for Electronics

Workshop

General Workshop Rules

Electrical Safety Principles

Electrical engineering an over view

Study of Electric Power supply

Study of safety devices

FUSES

Circuit breakers

Earthing

House Wiring

5.

Conduit Wiring

Tools used in Electric Wiring

STUDY OF WIRING ACCESSORIES

Switches

Ceiling Rose

Socket-Outlets

Plugs

Lamp Holders