Eat105 Chapter 1

CHAPTER 1

Introduction to Electrical Installation Design

EAT 105-Fundamental of Electrical Engineering

ELECTRICAL INSTALLATION DESIGN

Design of Power Distribution System in Buildings

The best distribution system is one that will,cost effectively and safely, supply adequateelectric service to both present and futureprobable loads

Function of the electric power distribution system

To receive power at one or more supplypoints and deliver it to the individual lamps,motors, and all other electrically operated

devices.


Basic Principles or Factor Requiring

Consideration During Design

• Functions of structure, present and future.• Life and flexibility of structure.• Locations of service entrance and

distribution equipment, locations and characteristics of loads, locations of unit substations.

• Demand and diversity factors of loads.• Sources of power; including normal,

standby and emergency.• Continuity and quality of power available

and required.• Energy efficiency and management.• Distribution and utilization voltages.• Bus and/or cable feeders.• Distribution equipment and motor control.• Power and lighting distribution boards and

motor control centers.• Types of lighting systems.• Installation methods.• Power monitoring systems.• Electric utility requirements.


Goals of System Design

1) SafetyTo design the power system which will notpresent any electrical hazard to the peoplewho utilize the facility, and/or theutilization equipment fed from the electricalsystem

2) Minimum Initial InvestmentThe owner’s overall budget for first costpurchase and installation of the electricaldistribution system and electrical utilizationequipment will be a key factor indetermining which of various alternatesystem designs are to be selected. Whentrying to minimize initial investment forelectrical equipment, consideration shouldbe given to the cost of installation, floorspace requirements and possible extracooling requirements as well as the initialpurchase price


Goals of System Design (Cont…)

3) Maximum Service ContinuityThe degree of service continuity and reliability needed will varydepending on the type and use of the facility as well as theloads or process being supplied by the electrical distributionsystem.

Typically, service continuity and reliability can be increased by:� Supplying multiple utility power sources or services� Supplying multiple connection paths to loads served� Using short time rated power circuit breakers� Providing alternate customers owned power sources

such as generators or batteries supplying uninterruptiblepower supplies

� Selecting the highest quality electrical equipment andconductors

� Using the best installation methods� Designing appropriate systems alarms, monitoring and

diagnostics� Selecting preventative maintenance systems or

equipment to alarm before an outage occurs



4) Maximum Flexibility & ExpendabilityIn many industrial manufacturing plants, electrical utilizationloads are periodically relocated or changed requiring changes inthe electrical distribution system. Consideration of the layoutand design of the electrical distribution system to accommodatethese changes must be considered

5) Maximum Electrical Efficiency (Minimum OperatingCosts)Electrical efficiency can generally be maximized by designingsystems that minimize the losses in conductors, transformersand utilization equipment. Proper voltage level selection plays akey factor in this area and will be discussed later. Selectingequipment, such as transformers, with lower operating losses,generally means higher first cost and increased floor spacerequirements; thus, there is a balance to be consideredbetween the owner’s utility energy change for the losses in thetransformer or other equipment versus the owner’s first costbudget and cost of money.



6) Minimum Maintenance CostUsually the simpler the electrical system design and the simplerthe electrical equipment, the less the associated maintenancecosts and operator errors. As electrical systems and equipmentbecome more complicated to provide greater service continuityor flexibility, the maintenance costs and chance for operatorerror increases. The systems should be designed with analternate power circuit to take electrical equipment (requiringperiodic maintenance) out of service without dropping essentialloads. Use of drawout type protective devices such as breakersand combination starters can also minimize maintenance costand out-of-service time.

7) Maximum Power QualityThe power input requirements of all utilization equipment hasto be considered including the acceptable operating range ofthe equipment and the electrical distribution system has to bedesigned to meet these needs


Low Voltage Distribution System (Principles)

MS

B

SSB 1

Main Distribution Level Sub Distribution Level Sub Distribution Level

SSB 2

SSB 3

DB

DB

DB

DB

DB

DB

DB

DB

DB

• Distribution from the MainSwitchboard (MSB)

• At this level, power from one ormore MV/LV transformersconnected to the MV network ofthe electrical utility is distributedto:- Different areas of the sites: shops in a factory, homogeneous production areas in industrial premises, floor in the office buildings, etc.- Centralised high power loadssuch as air compressors andwater cooling units in industrialprocesses or air conditionersand lifts in office buildings.

• Sub distribution used todistribute electricity within eacharea

• Final distribution, used to supplythe various loads


Low Voltage Distribution System (Principles)

Basic Topologies

All distribution systems are combinations of two basic topologies:

1. Star topologies: Radial or centralized distribution

2. Bus topologies: Distribution using busduct / busways (also referred to as busbar trunking system)

Star Topologies Bus Topologies


Selecting a Distribution Schemes

The LV distribution scheme is selected according to:• Energy availability requirements

The criterion of independent circuits to different parts of aninstallation makes it possible to:

1. Limit the consequences of a fault to the circuitconcerned

2. Simply fault locating3. Carry out maintenance work or circuit extensions

without interrupting the supply of power to the wholeinstallation.

• Size of the site (area & total power to be distributed)Small sites are supplied directly by the utility’s LV network andthe size and power requirements of the installation do notjustify a three level distribution system. Electrical distributionin all premises (stores, homes, small offices) most ofteninvolves only one or two levels.


Selecting a Distribution Schemes

• Load layout (equipment and power density)Two types of loads, depending on their layout on the site, must be taken in account:

• Concentrated load, generally corresponding to building utilities used for the entire site and requiring high power (e.g. centralized air conditioning units, lifts, refrigeration units in supermarket)

• Distributed loads that can be dealt with in groups corresponding to a homogeneous area (floor, factory shop, production line) and characterized by two parameters: power density (in VA/m2) and equipment density (in number of devices per 10 or 100m2)

• Installation flexibility requirementsInstallation flexibility is an increasingly important requirement, in particular for commercial and industrial premises.


Rules and Statutory Regulations

� Low-voltage installations are governed by a number of regulatoryand advisory texts, which may be classified as follows:

1. Statutory regulations (decrees, factory acts, etc.),2. Codes of practice, regulations issued by professional institutions,

job specifications,3. National and international standards for installations,4. National and international standards for products.

� The electricity supply and installation practice in Peninsular Malaysia are governed by the following:

1. Electricity Supply Act 1990 – Act 4472. Licensee Supply Regulation 19903. Electricity Regulation 19944. OSHA 1994 – Occupational, Safety & Health Act5. Malaysia Standard MS IEC 60364 Electrical Installation of

Buildings6. The current edition of the IEE Wiring Regulations for Electrical

Installations, where necessary (IEE Wiring Regulation 16thEdition)

7. Electricity Supply (Successor Company) Act 1990 – Act 448


Definitions of Voltage Ranges

� In Malaysia, the design criteria are developed byTenaga Nasional Berhad (TNB) for steady state supplyvoltage level fluctuation of the low voltage system canbe divided into:

Steady state voltage level fluctuation under normal condition: 415V/240V ±10% to +5%.

Steady state voltage level fluctuation under contingency condition: 415V/240V ±10%.


TNB Supply Schemes and Maximum Demand Level for Low Voltage System

MD Ranges of Individual Customer

Supply Voltage Typical Supply Scheme

Up to 12kVA 415V • Overhead services from LV mains

12kVA to 100kVA 415V • Three phase overhead or underground cable service from existing LV mains

100kVA to 1000kVA 415V • Direct cable services from LV board from a substation

Typical supply schemes for various Maximum Demand (MD) levels


No Type of Premises Minimum(kW)

Average(kW)

Maximum(kW)

1 Low cost flats, single storey terrace

1.5 2.0 3.0

2 Double storey terrace or apartment

3.0 4.0 5.0

3 Single storey, semidetached 3.0 5.0 7.0

4 Single storey bungalow & three room condominium

5.0 7.0 10.0

5 Double storey bungalow & luxury condominium

8.0 12.0 15.0

Range of Maximum Demand (MD) for domestic customer subclasses or premises



Range of Maximum Demand (MD) for types of shop houses


No Type of Premises Minimum(kW)

Average(kW)

Maximum(kW)

1 Single storey, semidetached 5 10 15

2 Double storey shop house 15 20 25

3 Three storey shop house 20 30 35

4 Four storey shop house 25 35 45

5 Five storey shop house 30 40 55


Rules and Statutory Regulations

Types of supply applications are provided by TNB canbe classified into three types:• Supply application for load up to 100kVA

� Supply usually from existing supply mains� Submission of applications to TNBD by Electrical

Contractor registered with Suruhanjaya Tenaga (ST)� Processing period for supply will take a maximum of 3

weeks upon approval from the local authorities.• Supply application for load exceeding 100kVA

� Supply may require establishment of new substation� Submission of applications to TNBD by Consultant

Engineer� Processing period for supply may take between 6

months to 3 years depending on the extent of electricalinfrastructure required.

• Supply application for streetlight� Application made by the local authority/government

department� Application by developer� Application by individual

Eat105 Chapter 1

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