Electrical Systems in a Building

Electrical Systems in a Building

Unit-IIBuilding Utility & Services

Syllabus

Introduction

• Since the end of the nineteenth century virtually all buildings are provided with electric lightings installation for use at night. With the advent of fluorescent lamp that is compatible with daylight, cheap to run and not emitting heat gain in buildings, it made possible to install electric lighting supplementing day light and in extreme cases provide the only source of light in a windowless environment. • Several factors can exercise a critical influence on the success of

lighting installations apart from proper level of illumination on the work plane.

Introduction

Introduction

• The first use of electric supply were established in 1882 by Thomas Edison, Thereafter there have been constant effort throughout the world to set-up power stations for more than one purposes.• The power generation in India in 1947-48 was only 4.1 billion and

today we generate more than 600 billion kw.

Electricity

Electricity Generation

Electric Generator

• Electricity is generated from the stored energy of water that makes turbine run and generate electricity. The other method includes fuels (Coal, diesel or gas) to fire boilers and pass stream and generate electricity through generators. Transformer step up several thousands or even hundreds of thousands of volts before it is supplied to the transmission lines or cable. By transmitting electricity at high voltages less power is lost in the cables. At the receiving end of voltage is stepped down by transforms in local sub-stations to consumers at 240 volts.

Electric Generator

Entry in the buildings

• In Urban areas electrical cables are Usually underground and are brought up to entry point at ground level or into basement service cable cannot be bent to small radiee and this should be borne in mind when considering point of entry. In small buildings the cable run is kept as short as possible, terminating in a distribution board at the first convenient position. In these buildings the distribution board will be fitted with a seal box to prevent moisture from entering the insulation of the service cable, a main fuse for the premises in a box sealed by the supply authority and the consumer unit or other switch and fuse gear belonging to the building. The position chosen for the distribution board should be readily accessible both for meter reading and for replacing fuses. In some cases special glasses are provided so that meter can be read without entering the premises.

Entry in the buildings

Domestic Supply

• Domestic electricity supply usually effected through distribution system and describe as single and three phases. Normally small buildings are supplied with electricity by two wires, one phase wire and the other neutral. This is known as single phase supply and gives a voltage for the premises of 240 volts. The loading of the supply wiring is balanced between the phases by using the phases in rotation so that each one services every third building. • In three phases, four wire bring 420/ 240 volts, 50 cycle per second. The

voltage. The voltage between any two of the phases wires is 415 Volts. And between any phase wire and the neutral is 240 volts. The balancing of load is then achieved by serving different areas of the building by different phases. Electric motor are usually designed for three phase operation.

Single and Three Phases Distribution

Earthing System• In electricity supply systems, an earthing system or grounding system is circuitry which connects parts of the electric circuit with the ground, thus defining the electric potential of the conductors relative to the Earth's conductive surface

Earthing System• Regulations for earthing system vary considerably among countries

and among different parts of electric systems. Most low voltage systems connect one supply conductor to the earth (ground).• People use an earthing system mainly for these applications:• To protect a structure from lightning strike, directing the lightning

through the earthing system and into the ground rod rather than passing through the structure.• Part of the safety system of mains electricity, preventing problems

associated with floating ground and sky voltage.• The most common ground plane for large monopole antenna and some

other kinds of radio antenna.

Applications Of Earthing

• Protect human against lightning and earth fault condition• Protect the premises against lightning and earth fault condition• Provide low resistance and safe path for lightning and fault current• All metallic enclosure and extraneous conductive parts are at

equipotential• LV System Earth

Applications Of Earthing

Functions of Earthing Equipment Earth : Path for fault current, lower touch voltage, protection against

electric shock

Lighting Earth : Low resistance path to diverse the current under lightning attack.

Telecom Earth : Signal Earth, reduce noise and interference, stabilize DC supply voltage and prevent electric shock

Computer Earth : reduce interference, maintain supply voltages

Functions of Earthing

Two classes of protection

Class I protection – use of barrier/insulation and connection of protective conductor to

equipment metallic enclosure in order to protect against electric shock Class II protection – beside of the basic insulation, addition layer of insulation apply to the

enclosure. Therefore no extraneous conductive part. The additional layer is independent to the basic insulation so that under failure of basic insulation, it offers additional protection

Two classes of protection

Types of Earthing• Supply System – Neutral Earth• System Earth• Electrical Safety Earth• Lightning Earth• Generator Earth• Protection Earth (i.e. surge arrestor)• Telecom / Computer Earth• Shielding Earth• Integrated Earthling System (Advocated)• Electrostatic Earth (Clean Room / Hospital)

Earthling Arrangements

• TN System• TNS System• TN C S System• TN C system• TT System• IT System

Domestic Supply

Distribution Circuits• In most of the buildings electricity supply is divided into two types of sub circuit:

Lighting Load sub-circuit and power load Sub Circuit and finally for operation purpose into three phases circuit-lighting, socket outlets and fixed apparatus. • The sub circuit which gives supply to lighting load points is called lighting load

sub circuit. This circuit includes lamps, fans, tubes etc. As per Indian Electricity Rules. The following rating should be assumed• Filament lamp 60 W• Ceiling fan 60 W• Socket for radio, table fan 60 W• Flurecent tube 40 W • Mercury Vapour lamp 80 W

Basic wiring Systems

• Wiring in buildings is run either on the surface or canceled in the construction. Surface wiring is cheaper but its appearance limits its use. The type of wiring system available for use in buildings are sheated and conduit. Two or more wires consisting of metal conductors each having its own inuation is enclosed in a protective sheath known as TRSC tough rubber sheated. • Use of PVC for insulation and sheating is preferred as it gives

smoother and neater cables. This type of wire are well suited to surface use. For use in concealed wiring, conduit or metal channels should provide to protect wiring.

Basic Wiring Systems


• Types of wiring• There is wide choice of wiring; however one must keep in mind the safety

of men & material. The various types of wiring used are discussed below• Cleat Wiring• In this system of wiring, V.I.R or PVC Insulated wires are held to the

walls and ceiling by means of porcelain cleats which are fixed at distance of 0.5 m horizontally and 0.75 m vertically above the walls The cleat are made on two halves, one is known as base and the other is known as cap. The wirings are drawn in groves and finally tightened. This wiring is cheapest and require little skill and can be quickly installed.

Cleat Wiring


• Wooden Casing , Capping Wire • In this type of wiring, the casing is fitted on the walls and ceilings on

the wooden gutties which are fixed The size of casing and capping generally used is 20 mm x 12 mm for house wiring. This type of wiring is generally used for house wiring. It is cheaper as compared to lead sheated and conduit wiring, easy to Install.


• Lead Casing Wire • In this system of wiring, the wiring procedure is same except the wire

used in VIR covered with an outer sheath made of lead-aluminum alloy It is used in houses and industrial wiring. It has good mechanical protection and possibility of fire is less.


• C.T.S & T.R.S or PVC wire • In this system of wiring first of all teaks wood is fitted on the walls

and ceiling. The battern is tightened by drawing wooden screws in the gutties fitted in the wall an ceiling. PVC or CTS wire run on the battern and finally grappled by the joint clip. This type of wiring is suitable for domestic installations, commercial & Industrial buildings except where it is liable to mechanical injury.

C.T.S & T.R.S or PVC wire

Basic wiring Systems• Conduit Wiring • In this type of wiring system VIR or PVC are carried through steel or

PVC tubes as conduit in case of surface conduit wiring, the conduit is fitted on the surface of the walls by means of saddles and in case of concealed conduit wiring the conduit to facilitate the drawing of wires

Ducts for Electrical Distribution

• In addition to the wiring systems there are a number of ducts available specially designed to contain electric cables in particular building stations

• Duct tube: It consists of an inflatable rubber tube, which is placed, in concrete formwork before pouring concrete. After the concrete has set the duct tube is deflated, withdrawn from concrete, leaving a duct for electric wiring, or other purpose.

• Skirting trunking: It is very usual to run cable trunking in or above the skirting round the perimeter walls. This systems is mostly employed in office buildings.

• Floor Trunking: System is employed in large offices where desks are placed remote from walls. Useful where there are comparatively few points, the positions of which are known, and where flexibility for future re-planning must be achieved.

• Overhead distribution• Overhead distribution systems are clearly more economical and more flexible than under floor ones.

They are mainly used in industrial units when pendants connection to apparatus is not considered unsightly.

Ducts for Electrical Distribution

Conductor

• Cables • A cable is a length of single conductor, usually having several

wires stranded to-gather, or of two or more conductors, each provide with its own insulation and laid up to-gather. The insulated conductor (s) may or may not be provided with an overall protective covering. The conductor with its insulation but without mechanical protection is called core of the cable. Thus a, cable consists of three parts: Conductor, Insulation and External Protection

Conductor

Insulations

• On the basis of of insulations, the cables maybe classified as follows: (i) Paper Insulated cables. In these cables paper is wound on the conductor in successive layer to archive required dielectric strength. Such cables are manufactured in various sizes from 5 mm2 to 500 mm2 cross-section conductors and voltage rating sup to 33 kv• (ii)PVC cables • (iii) Oil filled insulated cables• (iv)High Pressure of filled cables • (v) Compressed gas insulated cables• (vi) Vulcanized cable

Insulations

External Protection

• Against mechanical damage or electrochemical attack, fire or any other deterious influences external to the cables can be minimized. If certain points are taken in account• Abrupt bending in cables is not desirable; the bending radius ranges

from 12 to 30, times the diameter..• Cables should be at least 1 m away from the foundation of the

buildings.• Cables should be at least 0.5 m away from the communication cables• Whenever a cable crosses a road or railway line, it should be laid in

pipes or conduits.

External Protection

Electrical appliances

• There are many ways in which electricity can be used to save labour in the home. A vast number of appliances are designed to run on the ordinary domestic supply. The three basic application of electricity are – the production of heat, light and power and in many devices they are used in combination. Electronic appliances such as radio and television sets, and record players constitute a fourth class and telephone a fifth.• All the electrical appliances requiring a current of more than 5 A

should be fitted with an earth or ground wire to safe guard the user against shocks from leakages of current. Their supply cables thus carry three-pin plugs, and in the best type of socket no current can flow until the earth-pin can be made its contact.

Electrical Appliances

Electrical appliances• There are four main ways in which electricity can be converted into light• It can flow through a wire, so that it glows(lamps), modern filament lamps use

coil of tungsten wire which gives a much whiter light than carbon, and the bulb contains nitrogen and argon. Most household bulbs are 25 to 150 watt of electric power, but some large tungsten lamps used in search lights an in television studios use as much as 30 kw.• Discharge lamps are long tubes containing a gas or vapour. When electricity

passes through a pure gas at low pressure, energy is transferred to the gas atoms, causing them to emit radiations. The wavelength of this radiation, which determines color, depends on the gas e.g., sodium vapor and neon emit visible radiation. Sodium produces an efficient yellow light, mercury produces a bluish white light and some ultra-violet radiations, and neon gives off a strong red light.


• Fluorescent lamps

• Works by the conduction of electricity through mercury vapor. This causes the emission of ultra-violet radiation. The inside of the tube is coated with a fluorescent powder, or phosphor. This glows with a visible light when it is struck by invisible ultra-violet rays. The light is usually white, but it can be colored by adjusting composition of the phosphor. Sometimes, instead of tubes, flat panels of glass may be used as light sources. Some phosphors, such as zinc sulphide, emits light when a voltage is applied across them. This is known as electro luminescence..

• A carbon lamp consists basically of two carbon rods connected to an electricity supply. An electric arc is maintained between the rods and a very intense light is produced in this way from a compact source, such lamps are used in motion picture projectors.

Electric Installations• Electric Installations• Electric Installations require necessary design, planning taking into consideration the

whole requirement of the activities to be carried out in the building. The following steps are suggested for the same..

• Planning & Designing• Layout of working drawings• Application to electric supply company for granting estimated low supply and

requirement of sub-stations/ transformers • Laying conduit for underground supply lines before concreting and completing the plinth

work.• Laying conduits in slabs and beam reinforcement, fixing of fan hooks/ boxes in slabs

reinforcement for main supply to consumer units/ rooms

Electric Installations

• Physical marking of layout of wiring in all units/ rooms.• Providing & laying complete wiring• Fixing all fittings and fixtures and complete electrical installations• Testing of Installations• Providing consumer meters.• Submission of test reports to electric supply company for supply connection

after obtaining NOC from PWD in cases of building exceeds 15m height.• Checking of electrical installation by authorized officer of electrical supply

company before passing & sealing of meters.• Permanent electric supply connection to buildings and consumer thereof.


• Design & Planning• The design and planning of an electrical Installation is governed by

the type of user of the building and requirement of the consumer thereof. Therefore it is essential to consult competent electrical engineer/ licensed electrical contractor at the planning stage for providing and planning electrical installations, which should be safe and efficient in its use and adequate for its intended purpose. For designing layout of electrical installations for specific requirement of power use it is essential at planning stage that the architect in consultation with structural engineer, electrical engineer and owner/developer to decide about following


• Needed accommodation for making provision of sub-station, meter room, switch room, services cable duct, rising mains and cables, opening and chases required in floors and walls for intending electrical installations.• Total load requirement i.e. lights, fans, power etc.• Anticipated future increase in power consumption. Requirement of electric

supply company including location and distance of main supply connection point.• Layout of wiring installation, whether open conduit or concealed• After collecting necessary information and suggestions from other

consultants the architect should prepare detailed working drawing of complete electrical installation in consultation with licensed electrical contractor

Execution

• The execution of entire electrical Installation should be carried out under the guidance and supervision of competent electrical engineer/through licensed electrical contractor; in accordance to the design and specification provided in the tender and strictly as per rules and regulations of electrical supply.• The electrical contractor should decide his sequence of work in

consultation with the architect in such a manner that it will not affect/conflict with working of other agencies and it will allow other service agencies to work smoothly and simultaneously without any interruption.

Execution• The electrical contractor should get approval for all materials including

fitting and fixtures to be used from the architect before commencement of work.• The contractor should arrange temporary electrical supply for

construction purpose; before proper work is commenced.• At the end of work the electrical contractor should check and test the

entire electrical installation work and get it approved from the electrical supply company.• The electrical contractor should submit his test report and completion

certificate in required forms for consumer meter and permanent electric supply connections to the buildings.

Execution

Execution• Electric Services for Multi-storied Buildings• The electrical distribution cables wiring should be laid in a separate duct. The duct should be sealed at

every alternate floor with non-combustible materials having the same fire resistance as that of the duct.• Water mains, telephone lines, intercom lines, gas pipe lines should be laid in the duct of cables• Separate circuits for water pumps, lifts, staircase and corridor lighting and blower for the pressurize

system should be provided from the main switch gear panel.• The inspection panel doors and any other openings in the shaft should be provided with air tight fire

doors having a fire resistance of not less than two hours.• Medium and low voltage wiring running in shafts, and within a false ceilings, should run in metal

conduits.• An independent and well ventilated service room should be provided on the ground floor.• PVC cables should have an additional sheathing or protection provided by compound sprayed on after

installation

Staircase & Corridor lighting

• The following provisions have been recommended under the development control regulations. • The staircase and corridor lighting should be on separate circuit and

should be independently connected so that they could be operated by one switch installations.• Stair case and corridor lighting should also be connected to alternate

supply as defined in sub regulation.• Emergency lights should be provided in the staircase/Corridor for

multi-storied special buildings.

Staircase & Corridor lighting

Alternate Source of Electric Supply

• A stand-by electric generator should be installed to supply power to staircase and corridor lighting circuits, fire lifts, the standby fire pumps, smoke extraction & damper systems in case of failure of normal electric supply. • The generator should be capable of taking starting current offal

machines and circuit s stated above simultaneously. If the stand-by pump is driven by diesel engine. The generator supply need not to be connected to the standby pump.

Alternate Source of Electric Supply

Distribution board

•A distribution board (also known as panel-board or breaker panel) is a component of an electricity supply system which divides an electrical power feed into subsidiary circuits, while providing a protective fuse or circuit breaker for each circuit in a common enclosure.

Distribution Board

Transformers

•A transformer can accept energy at one voltage and deliver it at another voltage. This permits electrical energy to be generated at relatively low voltages and transmitted at high voltages and low currents, thus reducing line losses and voltage drop

Transformers

Location of Transformer

• Location of the transformer is very important as far as distribution loss is concerned. Transformer receives HT voltage from the grid and steps it down to the required voltage.• Transformers should be placed close to the load centre,

considering other features like optimization needs for centralized control, operational flexibility etc. This will bring down the distribution loss in cables.

Types of Transformers

• Transformers are classified as two categories: power transformers and distribution transformers.• Power transformers are used in transmission network of

higher voltages, deployed for step-up and step down transformer application (400 kV, 200 kV, 110 kV, 66 kV, 33kV)•Distribution transformers are used for lower voltage

distribution networks as a means to end user connectivity. (11kV, 6.6 kV,3.3 kV, 440V, 230V)

Sub-Station Substation is a part of an electrical generation, transmission,

and distribution system, where voltage is transformed from high to low, or low to high, or many other important functions.

Electric power may flow through several substations between generating plant and consumer, and may be changed in voltage in several steps.

Mainly Sub-station is defined as “The assembly of apparatus used to same some characteristics (e.g. Voltage, AC to DC, P.F. , Frequency etc.) of electric supply is called Substation.”

Sub-station Layout

A:Primary power lines' side 1.Primary power lines 2.Ground wire 3.Overhead lines 4.Transformer for measurement of electric voltage 5.Disconnect switch 6.Circuit breaker

7.Current transformer 8.Lightning arrester

B: Secondary power lines' side7.Current transformer 8.Lightning arrester 9.Main transformer 10.Control building

11.Security fence 12.Secondary power lines

The Electric Act 2003

• The electricity act 2003, seeks to bring about a qualitative transformation of the electricity sector through a new paradigm. The act seeks to create liberal framework of development for the power sector by distancing government from regulations. • The objectives of the act are to consolidate the laws relating to generation,

distribution trading and use of electricity and generally for taking measures conductive to development of electricity to all areas, nationalization of electricity tariff, ensuring transparent policies regarding subsidies, promotion of efficient and environmentally benign policies, constitution of Central Electricity Authority, Regulatory Commissions and established of Appeallate Tribunal and for matter connected thereafter or incidental thereto”.

The Electric Act 2003• The salient features of this act• The central Govt to prepare a National Electricity Policy in Consultation with State Govt.+• Thrust to complete the rural electrification and provide for management of rural distribution

by Panchayats, Cooperative Societies, non-government organizations, franchises etc.• Provision for license free generation and distribution in the rural areas.• Provision for private licenses in transmission and entry in distribution through an

independent network.• The state Electricity Regulatory Commission is a mandatory requirement.• Metering of all electricity supplied made mandatory.• Provisions relating to theft of electricity made more stringent.• Provisions safeguarding consumer interests.

References

Building Services: S.M. Patil Internet Websites

Thanks..

Electrical Systems in a Building

Engineering

Transcript of Electrical Systems in a Building