Typical Electrical Design philosophy

Design Philosophy January 1, 2015

WAMBASI BUTETE (BSC.ENG) 1

ELECTRICAL DESIGN PHILOSOPHY.

1.0 Introduction.

The design considers the proposed hotel as a commercial building, the

fundamental objective of commercial building design criterion is to provide;

Safe

Comfortable

energy-efficient

Attractive environment for living, working and enjoyment.

The electrical design must satisfy these criteria if it is to be successful.

Commercial buildings, because of their size and complexity, are dependent

upon adequate and reliable systems.

The complexity in nature of such a modern commercial building demands

keen analysis of the electrical and electronic system requirements.

1.1 Electrical Design Considerations.

The systems, equipment, and facilities that must be provided to satisfy

functional requirements for this type of facility are;

1. Building electric service and power distribution system.

2. Lighting Interior and exterior, both utilitarian and decorative; task and

general lighting.

3. Communications systems.

4. Fire alarm systems smoke and fire detection and emergency public

address systems.

5. Transportation: Elevators and dumbwaiters.



6. Electric fence, burglar alarms, electronic access systems, and closed-

circuit surveillance television.

7. Lightning protection.

8. Entertainment facilities and specialized audio-visual systems.

9. General electrical Safety.

10. Energy efficiency and conservation.

The goals and objectives are to provide uniformity of design by application of

standards; combining the best overall economy with suitability of design; and

be compatible with all other building systems. Provision shall be made for the

addition of future electrical loads.

1.1.1 Building electric service and power distribution system.

(a) Electric Power Supply.

Main electricity supply will be Kenya Power Supply, complimented by a stand

by generator in case of power black outs.

(b) Kenya Power transformer and Standby generator.

Main electricity supply from the Kenya Power Supply grid will be stepped down

to utility voltage using a step down transformer, Located in the main building

basement. A standard transformer room was specified for this use. A standby

generator is interconnected to the transformer and supply via electronic

changeover switching and controls provided in the switch room.

(c) Kenya Power transformer and Standby generator rating

and sizing.

Load calculations are performed to determine the rating and sizing of both

the generator and transformer, based on design load and anticipated future

additional load.



(d) Power Distribution.

Proper conductor sizes were obtained through standard load calculations.

Most important is that the current rating of a circuit should not be less than

the current demand of the circuit.

Formulae as provided in the IEE Wiring regulations 17th Edition (BS 7671:2008)

will be used in power calculations and design.

Selection of suitable conductor size is based on the quantity of load and thus

current anticipated. This is obtainable from calculations and reference to

standard cable rating tables.

Protective devices; every circuit must be protected by one or more devices

for automatic interruption of the supply in the event of overcurrent resulting

from:

Overload

Fault.

The following devices are acceptable as protective devices against

overcurrent:

Miniature Circuit Breakers (MCB)

Moulded Case Circuit Breakers (MCCB)

Semi-enclosed Fuses

Overload protective devices and fault current protective devices should

satisfy the requirements of BS Codes 9B, 9C, 9D and 9E. For devices providing

protection against both overload current and fault current, they should satisfy

both the requirements of overload protective devices and fault current

protective devices.

The characteristics of devices for overload protection should be coordinated

so that the energy let-through by the fault current protective device does not



exceed that which can be withstood by the overload protective device

without damage.

Voltage drops affect cable sizes. The Regulations require that the voltage at

the terminals of fixed equipment should be greater than the lower limit

permitted by the British Standard for that equipment, or in the absence of a

British Standard, that the safe functioning of the equipment should not be

impaired. These requirements are fulfilled if the voltage drop between the

origin of the installation and any load point does not exceed the following

values (IEE Regulations. Appendix 12) (Table 3.1 below). Standard cable

current ratings are tabulated against voltage drop in milli-volts (mV) dropped

for every ampere of design current (A), for every metre of conductor length

(m), case of Tables 9D1, 9D2, 9D3, 9E1 etc. in BS Code i.e.

Table 3.1

Lighting Power

3% 5%

240V Single phase 7.2V 12V

415V three phase 12.5V 20.8V

1.1.2 Lighting Interior and exterior, both utilitarian and decorative; task and

general lighting.

(a) Interior Lighting.

Key considerations prior to design are;

The dimensions of the room; Length, Width and mounting height of the

luminaire from working plane.

The nature of ceiling, walls, and floors in terms of colour and material.



The functionally/use of the design area to be illuminated.

Non analytical factors affecting the choice of luminaires, aesthetics

and natural lighting.

Interior lighting design will aims at determining the number of lighting fixtures

(luminaries) required in order to achieve the recommended illumination for a

given task.

In determining the number of lighting fixtures (luminaries) required, key among

other factors; the following has to be established:

Recommended illuminance (Lux) in Lumens/m²

Utilization factor

Maintenance factor of the Luminaire

Nominal lamp Luminous flux/output in Lumens.

Quantity of light here is specified by illuminance which is measured in lux.

(b) Outdoor and Landscape Lighting.

The goals of outdoor and landscape lighting are both practical and aesthetic.

Outdoor lighting design will addresses each of the following goals.

i. Security Lighting. Proper placement, coverage, and quality of the

illumination greatly determine the level of security.

The approach is to create a strategic lighting plan that illuminates

several key areas of the property with low levels of illumination. The low

levels allow the viewer to see objects in the illuminated areas and to still

see details in adjacent unlit areas. This is possible because the human

eye is able to compensate for a narrow range of illumination.

Key Considerations



o Low brightness illumination preferred to high brightness

o Broad coverage preferred to isolated areas of illumination

ii. Safety Lighting. Safety refers to providing illumination that offers safe

passage through the property. It especially targets steps, pools, water

features, and tripping hazards. As with the strategy for security lighting,

the illumination of hazards should be at a very low level - just enough to

discern details, but not so bright as to obscure surrounding dark areas.

Also important is that bulb filaments are not visible.

Key Considerations

o Target areas include pathways, steps, pools, water features,

tripping hazards

o Low brightness illumination preferred to high brightness

o Avoidance of 'light bombs.

iii. Task Lighting. Meant for usability, this goal identifies the need to provide

appropriate illumination for the various regions.

Key Considerations

o Fixture type, location, and brightness appropriate to the activity

o Illumination control options for multi-use areas.

iv. Aesthetic Lighting. This encompasses a wide range of human factors

and is the most subjective of the goals.

1.1.3 Communications.



To cover telephone, satellite link, room-to-room communications (including

microwave, computer link, radio, closed-circuit television, code call, public

address, fiber optic and electronic intercommunication videoconferencing ,

advertising and signage and a variety of other signal systems .

IP Telephony; Voice over IP (VoIP) methodology is the preferable technology

for the delivery of voice communications and multimedia sessions over Internet

Protocol (IP) networks.

Computer data communications; Internet communication between

computers will be by both wireless transmitters and receivers and structured

cabling.

Fiber optic and electronic intercommunication ; Fiber optics will be used to

provide high quality compressed signal communication, thus reducing on

cable space volume and ductwork .

Videoconferencing; Will use computer networks to transmit audio and video

data. The components required for a videoconferencing system include;

Video input : video camera or webcam

Video output: computer monitor, television or projector

Audio input: microphones, CD/DVD player, cassette player, or any

other source of Preamp audio outlet.

Audio output: loudspeakers associated with the display device or

telephone

Data transfer: Internet

Computer: a data processing unit that does the compressing and

decompressing, and initiates and maintains the data linkage via the

network.



A server room will be provided for communications.

1.1.4 Firefighting and fire protection.

This will comprise smoke and fire detection, alarm systems and emergency

public address systems, this will be provided at suitable locations of the

building. An addressable system will be implemented.

1.1.5 Transportation: Elevators and dumbwaiters.

Lifts to provide means of vertical transportation in the building, the dimensions

in terms of car height, rated speed, pit depth, height of the car door and

landing door, headroom, number of cars and speed are based on ISO 4190-

1:1999(E) for lifts. BS standards for lifts, BS 2655 and 5655 provide guidelines for

the lift installations.

1.1.6 Electric fence, burglar alarms, closed-circuit surveillance television and

electronic access systems.

Electric Fence ; An electric fence will be provided in some areas surrounding

the site area, the system shall consists of an electric fence energiser and be of

the alternate design. Fixed on posts in this alternate design carries both live

wires and earth wire, alternating live-earth-live etc. Earth electrode will be

made from copper or any galvanized steel material, and should be driven into

the soil at least 1.5m (5ft).

The live terminal of the energizer is connected to all of the "live" fence wires.

The earth terminal of the energizer is connected to both the earth electrode

and the earth wire(s) on the fence. The ground conduction path is under the

500~1000m suggested maximum distance therefore earthed only once.



Electric Fence posts will use galvanised or stainless steel earth stakes. Electric

fence warning signs must be placed at regular intervals along electric fences

where there is a possibility of the general public coming into contact with the

fence.

Electrical power supply to the low power energizer will be an Input Voltage of

240Vac 50Hz nominal supplied by 2.5mm2 insulated copper cables.

Burglar alarms and CCTV; this will be through a system of interworking

components and devices. The system will include the following:

A control panel, which is the primary controller of the security system

Door and window sensors

Motion sensors, both interior and exterior

Wired or wireless security cameras

A high-decibel siren or alarm

A yard sign and window stickers

A CCTV control room for a professionally monitored security system

being proposed for the facility. The room will be equipped with

chairs, monitor mounts, lighting, racking cabinets, drawer pedestals,

storage units, desk actuation, and equipment up stands.

Electronic access system; this will be provided for selective restriction of access

to a places. Electronic Locks and login credentials will be the major

mechanisms of access control. Access will require authentication. There are

three types of authenticating information to be used.

something the user knows, e.g. a password, pass-phrase or PIN for

security personnel

Something the user has, such as smart card or a key fob for guests.

Something the user is, such as fingerprint, verified by biometric

measurement for staff.



1.1.7 Lightning protection.

Lightning protection will be provided for lightning safety. The protection system

will comprise Lightning conductors and accessories, air terminals and

accessories, air terminal bases, braided lightning conductor, cable connectors

and clamps, Thru-Roof Wall Connectors Assemblies & Accessories, Brass Ball

Studs, bonding lugs and plates and a lightning warning system.

The general design rules for lighting protection will be adopted. The buildings

must have two groundings as widely separated as possible, preferably at

diagonally opposite corner. Cables shall be free of sharp turns and "u" or "v"

pockets. Cables shall remain horizontal or on downward path towards the

ground.

1.1.8 Entertainment facilities and specialized audio-visual systems.

Cable television and piped music will be provided at specific locations. At the

entrance waiting lobby, other screens will be provided for advertisement and

presentations.

1.1.9 General electrical Safety.

This to include but not limited to;

Cable sizing and protective device sizing.

Discrimination of low and high voltages.

Testing and conformance of installations to local and international

standards.

Proper insulation for components connected to power points near wet

areas including sinks, baths and swimming pools.

Extension leads or power leads not to be used in wet areas unless

specifically designed to do so.

Positioning extension cords along walls and around furniture.



Extension cords should have 3 pins (plugs with 2 pins are not earthed and

should be used only with double insulated electrical equipment).

Cords should not be draped over benches where they can be caught

or grabbed.

Ladders, boat masts and poles should be kept well clear of overhead

power lines.

Clearly indicate where switchboard is located and Keep access to

switchboard free of obstructions

Labelling switches, circuit breakers, fuses, control units and distribution

boards.

Installation work must be undertaken by a licensed electrical contractor.

Placing warning signage on all areas with high voltages and equipment

rooms.

1.1.10 Energy efficiency and conservation.

Energy efficiency and measures to be implemented through the project

cycle to cover the following major areas.

Energy efficient lighting to be used as LED lighting, compact fluorescent

light bulbs (CFLs) and fluorescent with electronic ballast.

Photocells and timers to be fitted to external lights with motion-

detectors.

Use of ENERGY STAR® labelled light bulbs, home appliances, electronics,

and other products. ENERGY STAR products meet strict efficiency

guidelines set by the U.S. Environmental Protection Agency and the U.S.

Department of Energy.

Place lamps in corners where possible so they reflect light from two walls.

Installation of solar water heater to save energy by using solar power.



Laptop computers should be used – they use less energy than desktop

computers.