Specification for Electrical Work
Low Voltage Electrical Distribution System
Scope
Scope of Work
The Contractor shall carry out the supply, delivery, erection, connection, testing and
commissioning of all the equipment and material for the complete LV Electrical Distribution
System of the building. The installation shall include but not necessary be limited the
following:
a) Main distribution board
b) Floor distribution board
c) Sub distribution board/ Consumer units
d) Power cables – indoor & outdoor
e) Final circuits from sub distribution boards/ consumer units
f) Lighting system – indoor & outdoor
g) Small power installation comprising power socket outlets
h) Ceiling fans and exhaust
i) Earthing system
Power Supply
Main (regular) power supply for the building will be taken from the Ceylon Electricity Board
(CEB) using 95 kVA Bulk Supply.
Stand-by (emergency) power supply for the building complex will not be provided by a
standby diesel generator.
General Requirements
Drawings
Positions shown in the tender drawings for electrical equipment, lighting fixtures, power
socket outlets, etc. are approximate and actual position shall be decided at the site, and shall
be marked on the Contractor’s shop drawings.
Samples
The contractor shall formally submit samples of materials and items of equipment for
approval of the Engineering Consultant before installation.
Experience of Contractor
Work shall be carried out by an experienced electrical contractor who has previous experience
in similar projects and shall have necessary tools, equipment and experienced staff for
electrical installation and testing.
Low Voltage Switchgear
Main Distribution Board
The main distribution boards shall be of the rigid, freestanding, metal cubicle type, totally
enclosed, dust and vermin protected and factory fabricated from 3b in compliance with BS
5486(IEC 60439) and this specification where applicable.
Finished panel shall be without sharp edges and all exposed screws, bolts and similar
fastening shall be smooth surfaced and protectively plated to prevent rusting.
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Enclosure protection class, including cable connection chamber, shall be IP 54 as a minimum.
Main distribution board shall be provided with a metal plinth minimum 75mm high.
The distribution board shall comprise the equipment indicated in the BOQ schedule together
with all current transformers, auxiliary fuses, protection relays, small wiring and
interconnections.
The distribution board shall be flush fronted with front and rear access, suitable for indoor
use. Access doors and covers shall incorporate sealing gaskets.
Busbars shall be of H D H C tinned copper. Phase and neutral bars shall have the same cross-
sectional area, with a current carrying capacity as indicated in the schedule.
A tinned copper earthing bar complying with BS 1432 sized to withstand the short time
current of the distribution board shall be securing fired to and extend the full length of the
distribution board and be connected to an earthing terminal at each end. All metal work(other
than current carrying parts) shall be bonded to the earthing bar and provision shall be made
for bonding the armoring and metal sheath of incoming and outgoing cables.
All internal wiring shall be carried out neatly and shall wherever possible be housed in wiring
trunking forming an integral part of the distribution board.
Connection facilities for outgoing circuits shall be provided at the top and bottom of the
distribution board as appropriate for the feeder. Incoming connections shall be from the
bottom.
All live terminals and components within any panel shall be shielded in such a manner as to
prevent inadvertent contact with them. All live terminals and components mounted on panel
doors shall be shrouded such that contact can only be made after removal of the shroud.
A high standard of finish is required for the distribution board. The finish shall be a powder
coating applied electro statically. Before painting the Contractor shall submit to the Engineer
for approval, detail painting scheme.
Before manufacture, the Contractor shall submit to the Engineer for approval, detail drawings
showing the layout, construction and connection of the distribution board.
Distribution Boards
Floor Distribution Boards, Sub-Distribution Boards and other Distribution Boards shall
comply with the requirements specified for the Main Distribution Board, Except the size and
equipment mounted on it. Equipment such as MCCBs, MCBs, RCDs, etc. to be mounted on
each Distribution Board shall be as given in the Bill of Quantities and/or drawings.
Distribution Boards shall be of wall-mounted type unless otherwise specified.
Consumer Units
Consumer Unit shall in general comply with the specification of sub distribution board
except that the enclosure of the consumer unit shall be made of non-breakable plastic and
provided with a transparent door.
Consumer Unit shall be in-general flush fronted, suitable for wall recess mounting.
Consumer Unit shall comprise the equipment indicated in the drawings together with all
terminals, busbars, small wiring, interconnections etc.
Moulded Case Circuit Breakers
Moulded Case Circuit Breakers (MCCB’s) shall comply with IEC 60947-2.
The operating mechanism shall be of the quick-made, quick-break, trip-free type with the
speed of operation independent of the operator. The mechanism shall be designed to operate
all poles simultaneously during opening, closing and tripping conditions.
The breakers shall be operated by a toggle unless otherwise specified in the schedules,
drawings or bill of quantities.
The breakers shall be provided with thermal bi-metallic elements for an inverse time-current
trip characteristic to protect against sustained overloads and instantaneous magnetic trip
elements for short circuits protection.
Thermal trips shall be adjustable. A single adjustment shall ensure the setting of all poles in a
multi-pole breaker simultaneously.
Tripping time of the breaker shall be adjustable.
Miniature Circuit Breakers
The miniature circuit breakers (MCBs) shall comply with BS 3871 Part I and shall have a
Type 2 Classification. The current rating and short-circuit breaking capacity shall be as
indicated in the drawings and/or bill of quantities a minimum short circuit rating of 6KA shall
apply.
The frame size of all MCBs shall be of the same so that they can be easily interchanged.
Circuit breaker dollies shall be of the trip-free pattern to prevent closing the breaker on a
faulty circuit and they shall be engraved to indicate the ON/OFF position.
Residual Current Devices
Residual Current Devices (RCDs) shall provide accident protection by interrupting dangerous
contact voltages, which may be present in faulty electrical appliances as a result of frame
faults, insufficient insulation on misuse. They shall provide a high degree of protection
against earth faults, fires and electric shock.
RCD shall conform to BS 4293 and shall be sensitive to pulsating DC fault Current.
Each RCD shall consist of a current transformer, a tripping coil with contact assembly, main
supply contacts, ON/OFF switch, a test button and trip-free mechanism, all mounted on
robust body of all insulated material. RCD shall be suitable for operation on 230V, 1-ph,50Hz
supply and shall give trouble-free service in the locally prevailing climatic conditions.
The tripping current shall be 30 mA unless otherwise specified.
Power Analyzers
The following measurements shall be possible with the Power Analyzers.
Instantaneous RMS values
Active power (kW) and reactive power (kV AR) – total and per phase
Current (A) – 3 phases and neutral
Voltage (V) – phases to phases to neutral
Frequency (Hz)
Apparent power (kV A)
Power factor
Energy values
Active energy (kWh)
Reactive energy (kV AR)
Demand values
Maximum active power demand(kW)
Accuracy of multi function power meter shall be not less than the following
Energy and power accuracy : 2%
Current and voltage accuracy : 5%
All current Transformers, Potential Transformers required for power Analyzers shall be
provided.
Surge Protection Devices (SPD)
Surge Protection devices installed shall be according to the standard IEC 62305-4 SPD
installed. Protection level <= 1.4kV, shall be applicable to these SPD.
Testing of Low Voltage Switchgear
Testing of main distribution board, floor distribution boards & sub distribution boards shall be
carried out at the manufacturer’s workshops witnessed by the Engineer/Consultant. All the
costs including travelling. Lodging etc of the Engineer/Consultant in connection with witness
testing shallbe borne by the Contractor.
Cables, cable Trays and Conduits
General
The cables shall be sized to comply with the regulations for Electrical Installations published
by the Institution of Electrical Engineers, London, except where specified sizes of cables are
shown on the drawings or detailed elsewhere in the Specifications or Schedules.
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No cables conductor shall be less than 1.0 mm cross sectional area.
Preferred colour coding shall be as follows:
Function Colour
Phase L1 Brown
Phase L2 Black
Phase L3 Grey
Neutral N Blue
Earthing Yellow/green
Feeder Cables
Feeder cables from the Main Distribution Board and Distribution boars shall be of
Cu/PVC/PVC or Cu/XLPE/PVC multi-core cables and shall be of 600/1000 Volt grade
complying with BS 5467 or IEC 60502.
Cable size shall be as indicated in the drawings and/or bill of quantities.
Wiring Cables
Cables of final sub-circuits, from distribution boards to lighting points, socket outlets, fan
points etc., shall be of PVC sheathed copper conductor cables complying with BS 6346 or
BS 6004 as applicable.
Armoured Cables
Armoured cable shall be installed directly buried underground. The cable buried underground
shall be approved by the Engineer. All cable buried underground shall be laid 800mm below
ground level and covered with concrete cable tiles. Cable trench shall not be closed without
the consent of the Engineer. Where cable enter building underground or pass paved area they
shall 100mm dia. PVC duct. Where specifically indicated, armoured cables may be installed
in cable tray.
Cable installed outdoors such as outdoor lighting circuit cables shall be of XLPE-insulated
PVC sheathed steel wire armoured copper conductor multi-core cables shall be of 600/1000
Volt grade complying with BS 5467.
Unarmored Cables
All XLPE insulated unarmoured cable shall be installed in cable tray and/or drawn through
securely fixed conduits as applicable.
Cables – Installation
Cable routes are indicated on the drawings for tender purposes but exact final routing shall be
agreed with the Engineering Consultant.
All work shall be carried out by the Contractor who is to include for the supply and
installation of all jointing materials, cables, supports, steel work racks and making all
necessary terminations. The cables shall be installed and tested in accordance with the
appropriate Clauses of the IEE Regulations (BS 7671).
Cables shall at all times be handled with care and every effort made to avoid damage.
Unloading, rolling to position and mounting of cables drums shall be carried out efficiently
and carefully in the recognized manner and cable shall be pulled from the top of the drum and
twisting shall at all times be avoided.
The Contractor shall take particular care to avoid damage to other services which may run
adjacent to or across the route of the cables being installed.
Where cables are run vertically, heavy gauge sheet metal guards shall be supplied and fixed to
the wall. The casing shall be fixed from floor level to the underside of the appropriate cable
termination or to a height of 1.5 meters above floor level. Detailed drawings showing
dimensions and method of manufacture of the cable guard shall be submitted to the Engineer
for approval.
All cables shall be firmly and adequately supported from cable hangers for the whole pf their
length except where they run through pipe ducts, cable trays or buried direct in the ground.
Expect for terminations at a factory made switchboard, distribution board or item of
switchgear, no joints shall be made between lengths of cable.
Cable Glands
The cables shall be terminated at the equipment served by a mechanical type, brass cable
gland conforming to BS 6121. For armoured cables, the gland shall be complete with
armouring clamp suitable for bondng the armouring to the unit served, by means of 25mm x
2.5mm copper tape and the bonds shall be carried out at the time of making the joints.
Cable Trays (with covers)
Cable trays shall be return flange perforated type of mild steel, hot-dip galvanized after
manufacture. For trays up to 300mm wide, thickness shall be not less than 16SWG and for
widths above 300mm thickness shall be not less than 14SWG. The cable tray shall be of
sufficient width to take all cables without crowding. Each length of tray shall be securely
bolted to an adjacent length with sufficient overlap to prevent sagging and twisiting.
The cable tray shall be fixed to purpose made steel brackets which shall in turn be fixed to the
structure. The brackets shall be hot-dip galvanized after manufacture and all holes are made
and finish painted in the same colour as the tray.
Certain length of the cable tray system may be fixed to a wall. The blance length is to be
suspended, from the upper floor slab. For this purpose steel fixing rods of required lengths
shall be provided. All fixing rods, associated steel work and nuts shall be galvanized.
Metal Conduits
Metal conduit shall be heavy gauge, galvanized steel tube, and screwed jointed type
conforming to BS 4568.
Conduit fittings shall be finished to the same classification of production as the conduits.
The conduits throughout shall be of sufficiently large section and so arranged with drawn-in
boxes to allow either an easy draw-in or out of any or all of the cables which must not exceed
the number set out in the appropriate table of the IEE Wiring Regulations. Conduit of less
than 20mm diameter shall not b used.
PVC Conduits
Conduits which are concealed in building wall plaster and used for internal lighting and
power installation shall be rigid, round PVC tubing conforming to BS 4607 (Metric).
The conduit shall be of sufficiently large section and so arranged with draw-in boxes to allow
either an easy draw-in or out of any or all of the cables which must not exceed the number set
out in the appropriate table of the I.E.E. Wiring Regulations.
PVC Conduit Boxes
All boxes and fitting shall conform to BS 4607 and shall be made of rigid PVC.
Boxes for switches, sockets, outlets, etc., shall be of rigid PVC and dimensions shall be
suitable for fixing switches, sockets and other accessories as applicable.
All boxes shall be provided with tapped brass inserts for fixing the screws and where
necessary to comply with the appropriate clauses of the IEE Wiring Regulations, With brass
earthing terminals,
All adaptable boxes and lids of the same size shall be interchangeable.
Lighting System
General
Luminaires shall be of the type as shown in the drawing and approved by the Project
Architect. All the luminaires shall be supplied and installed under the contract.
LED Light Fittings
LED fitting having , Efficacy > 90 Lm/W, CRI > 80, CE/TUC Certified constant current
driver (Europain or Japanese) use in 110-20 V range, colour > 5000K, LED chips Osram,
philiphs or equvalant
Light fitting Wattage LED(W)
Recessed type Niche light fitting 4
Surface mounted Panel lighted fitting 6
Recessed type Down Light fitting 6
Flood light (IP65) 15
Pendant type Light fitting 9
Mirror Light fitting 9
1200mm long complete with powder coated 20
White sheet steel housing
600 X 600 mm recessed panel Light fitting 36
Outdoor Wall Bracket light fitting (IP65) 9
Chandelier light fitting 50
Lighting Switches
These switches shall be of the flush mounting “rocker action” type complying with BS 3676.
The rocker and cover plate shall be constructed of “all insulated” white rigid plastic. The
switch mechanism shall be reted at 10A and shall be capable of being used on fluorescent or
inductive loads without de-rating.
The cover plates shall overlap the boxes.
Wiring of Small Power
The wiring system shall consist of XLPE/PVC insulated PVC sheathed copper cable and PVC
insulated protective conductor (earth wire) drawn through concealed PVC conduits or
exposed galvanized steel conduits. Conduit system and trunking system shall be installed
before drawing the cables.
Wiring may be carried out by using looping method but joint shall not be permitted in runs of
cable.
Socket Outlets – Flush Type
Socket outlets shall be switched, 3-pin (phase, neutral & earth), shuttered, flush mounted type
rated for 230V complying with relevant BS, as follows.
13A socket outlets to BS 1363
The finish and thickness of the front plate shall be similar to the lighting switches.
Ceiling Fans
1400mm ceiling fans shall be 3-blade type, complete with choke type regulator with 5 speed
positions conforming to BS 5060 or equivalent, In addition to the regulator there shall be a 10
amp switch to control the fan. Fan hook shall be made with 12mm MS bars, where necessary
rate shall include extending the fan rod and painting. Connection to the fan shall be through a
ceiling rose or connection bar.
Installation
Mounting Height and Position
Mounting height is indicated elsewhere, otherwise as indicated by the project Architect.
Where difficulty in locating accessories occurs the project Manager shall be informed.
Particular attention shall be paid to the positioning of light points in relation to the ceiling ,
position of switches in relationship to the hanging of door and accessories in relation to fixed
furniture, sinks and equipment. Switches shall be installed adjacent to the closing style of the
doors. The Contractor shall carefully co-ordinate with equipment/furniture supplier and the
Project Manager regarding the final position of the equipment.
Steel Conduits
The conduit system be a continuous and effective means of protection for the wiring. The
conduit shall be laid as far as possible in straight lines. The conduit is in no part to be under
mechanical stress.
PVC Conduits
The conduit system be a continuous and effective means of protection for the wiring. The
conduit shall be laid as far as possible in straight lines.
The conduit is in no part to be under mechanical stress.
Whenever possible, conduits shall be arranged so that the inspection or ‘draw-in’ points are
not required where conduit is sunk in concrete or plaster, ie. Cable to be drawn in only at
lighting, switches, plugs or other appliance outlets.
Exposed PVC conduits will not be allowed.
Testing of Electrical Installation
Testing of entire electrical installation of the building complex shall be carried out by the
Contractor. Test report/certificate as required per IEE building wiring regulation and certified
by a chartered Electrical Engineer shall be submitted.
Telephone & Data Wiring Systems
Scope
The contractor shall supply and install a wiring system for the telephone network and data
network as indicated in the drawings.
Telephone Wiring System
There will be one Main Distribution Frame (MDF) located in the Ground Floor which shall be
connected to the existing Private Automatic Business Exchange (PABX) system using a multi
pair telephone cables in cable trunking. On each floor telephone junction boxes shall be
installed. Individual telephone outlet circuits of each office shall be connected to the
telephone junction box of the respective floor.
Wiring shall be carried out with 0.5mm PVC insulated twisted pair telephone cables in
concealed PVC conduits.
Main Distribution Frames
The main distribution frames (MDF) shall be a wall mounted light-weight polycarbonate box
with lockable 180 degree opening door. Capacity shall be as shown in the drawing/Bill of
Quantities.
The terminal blocks shall contain solder terminals on the incoming side and screw-in
terminals for the outgoing cables. MDF must be included surge diverters to avoid the
damages of surges.
Telephone Junction Boxes
Telephone junction boxes shall be of the capacity specified on the drawings, comprising of
mounting frame or box with a cover containing a terminal block with solder terminals on the
incoming side and screw-on terminals for the outgoing pairs.
The junction boxes shall be of the flush mounted type unless installed inside a duct.
Telephone Socket Outlets
The telephone outlets shall be flush with a fixed telephone terminal block and a overlapping
white plastic cover plate having bushed flex outlets, with cord clamp and suitable for one or
two telephone flexible cords as indicated on the drawings. Telephone sockets shall be of the
type RJ 11.
Earthing System
The earth resistance shall be less than 5Ω measured on a dry or a lesser value as per the
requirement of the instruments offered. Suitable inspection pits shall be provided at each earth
rod for inspection and testing.
Testing of Telephone Network
On completion the installation the telephone wiring system, the Contractor shall perform the
following checks and tests.
• Check for the correct installation of all the items
• Check the correct operation of the entire installation
• Measure the continuity resistance of each circuit
• Measure the earth resistance of earth electrodes
The results shall confirm to the specifications and the requirements of the Director General of
Telecommunications.
Data (Local Area Network) Wiring System
Data(LAN) wiring system shall comprise of primary Network Switch, Secondary Network
Switches, Patch Panels, Faceplates with Keystone Jack and Wiring. Individual data outlet
circuits of each office shall be connected to the Patch panel of the respective floor.
Wiring shall be carried out with 4-pair CAT 6 unshielded twisted Pair(UTP) cable.
Data Socket Outlets
Data outlets shall be flush with a fixed terminal block and a overlapping white plasic cover
plate having bushed flex outlets, with cord camp. Socket shall be of the type RJ 45.
Testing of Data Network
On completion the installation the data network wiring system, the Contractor shall perform
the following checks and tests.
• Check for the correct installation of all the items
• Check the correct operation of the entire installation
• Measure the continuity resistance of each circuit
Lightening Protection Systems
Scope
The Contractor shall supply and install a lightning protection system conforming with the
requirements of IEC standards.
The system shall include, but not be limited to, an air termination network, down conductors,
joint and bonds, test joints, earth termination network and earth electrodes.
Applicable Standards and Codes
Lightning protection system shall confirm to the requirements of the following standard.
IEC 62305-2 : Protection against lightning-Part 2: Risk management
IEC 62305-3 : Protection against lightning-Part 3: Physical damage to structures
and life hazard
SLS 1261-2004 : Sri Lankan Standards for lightning Protection Systems
Air Termination Network
General
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The air termination network shall comprise conductors of 50mm (minimum) bare Copper
tapes fixed to the roof over roof sheets/tiles. Air termination network of these roof conductors
shall be supplemented by taper pointed air terminals (finials) fixed vertically on the roof at the
highest level.
All metal components- roof sheets, roof trusses etc. shall be connected to the air termination
network
Roof Conductors
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Roof conductors shall be 25mm X 2.5mm (62.5mm ) high conductivity bare Copper tapes to
BS 1432 Grade C101.
Air Terminals (Finials)
Air terminal shall be of taper pointed Copper rod, complete with base for mounting on the
roof. The rod shall be 12mm diameter and 0.5m length, threaded at one end and secured with
a lock-nut after being screwed in to the base.
Down Conductor Network
Down conductors shall be provided, consisting of circular mild steel conductors clamped to
the reinforcing bars and encased in concrete, to interconnect air termination network to earth
electrodes. Joints in the down conductors shall be kept to a minimum and any joints shall be
by welding. The Contractor shall ensure that the joints are mechanically and electrically
effective before a joint is covered.
Down conductors shall be installed without bends and without rising above the level of the
connection joints to the roof rods. Each down conductor shall follow the most direct path
possible between the air termination network and the earth electrode. Down conductors shall
be arranged as evenly as practicable around the outside columns of the building starting from
the corners.
Connections from the down conductors to roof conductors (tapes) and to test clamps/earth
electrodes shall be brought out of the concrete through a built-in bonding point. Connections
between roof rods and down conductors shall be with welded joints.
Each down conductor shall be provided with a test joint in such a position that, whilst not
inviting unauthorized interference, and convenient for tests. Down conductors shall be
connected to the steel reinforcements of the pile foundation.
Earth Termination Network
General
An earth termination network as per IEC 62305-3 shall be provided. An earth electrode shall
be connected to each Copper down conductor. The earth resistance of the earth termination
network shall not exceed 10(ten) ohms.
Earth Electrodes
Each earth electrode shall consist of 16mm diameter extensible type Copper clad steel rods
complete with driving stud, coupling dowels and spike. Each earth rod shall be 1.2m log.
Each earth electrode shall have resistance to earth not exceeding the product given by 10
ohms multiplied by the total number of earth electrodes connected to the earth termination
network.
The Contractor shall measure the resistance of each earth electrode immediately after it is
driven. If the earth resistance is more than the permitted value, the Contractor shall install
additional rods which shall be coupled to the rod already installed to obtain acceptable value
of resistance.
Each earth electrode shall have a concrete inspection pit (450mm in length, 450mm in width
& 450mm in depth) and cover provided.
Accessories
Lightning protection system shall be provided with all required test joints for down
conductors, fixing clips and clamps for Copper tapes and round conductors, earth rod clamps,
bonds to metallic items/parts and other accessories.
Exposed Metalwork
All exposed metalwork such as TV/Radio aerial masts, metal roof and the like shall be boded
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to lightning protection system using 50mm earth cables as required in IEC 62305-3, using
bonds and clamps appropriate to the location.
Tests
During the construction of the building structure, tests shall be made of the continuity of the
welded joints in the Copper down conductors before and after each pour of concrete is
completed.
On completion of the installation, the following tests shall be made:-
(i) Resistance to earth of the complete installation
(ii) Resistance to earth of each electrode
(iii) Electrical continuity of all bends and joints
In addition, a visual inspection shall be made of the entire installation with particular attention
being paid to fixings, joints and bends.
