0ELECTRICAL WORK FOR BUILDING CONSTRUCTION
INTRODUCTION
Electricity supply is a basic need of the modern world , since all appliances from lights , fans … etc. work on electricity .
The licensed person , in charge of the electrical work, should be given right instructions and layout plans for completing the electrical work satisfactory and safely.
It is necessary to study how the various types of loads are connected to the supply.
This helps in planning the requirement of materials , tools , equipments etc. before starting any work
TOOLS REQUIRED FOR ELECTRICAL WORK • Screw driver set
• Wire cutting pliers set • Hack – saw frame/ blade
• Drill machine with drill bits or bit punch holder • Chisel
• Hammer • Knife
• Tester / test lamp • Plumb bob • Level tube • Spirit level • Line dort • Measuring tape • Wire stripper
• Set of files
• Hand drill machine • Die/ vice set
PLANNING OF INTERNAL ELECTRICAL WORK
Planning is the most important factor before commencing any electrical work Design and planning should take into consideration the prevailing conditions at the site and the requirements of the consumer
Before starting the project , electrical drawings should be prepared along with all the drawings
Planning at the initial stages will help to decide the locations of each point in each room , specification of materials , required load for each flat and each building
By planning in the initial stages and preparing the drawings accordingly , chances of mistakes by an engineer are reduced considerably .
This results in economy of electrification work
(1)POSITION AND REQUIREMENTS OF ELECTRICAL POINTS
Position of the points depends on the requirements of individual flats . Following points will act as guideline…
• Fan points should be diagonally in the centre of the room , excluding the loft
• Width
• Switch boards should be nearest to the entrance , opposite the door opening
• Switches for the bathroom should be outside the door
• Consider the probable furniture arrangement before deciding the switch board and light points in the rooms
• Power point in the kitchen should be nearest to the kitchen platform REQUIREMENTS OF ELECTRICAL POINTS
SN O LOCATION LIGHT POIN T FAN POIN T POWE R POINT PLUG ON BOAR D PLUG POIN T BELL POIN T T V POIN T TEL POIN T 1 Living room 2 1 - 1 1 1 1 1 2 bedroom 2 1 - 1 - - - -3 Kitchen room 1 1 1 1 - - - -4 Balcony 1 -- - - -5 Water closet 1 - - - -6 Bathroom 1 - 1 - - - - -7 Passage 1 - - -
-(2)HEIGHTS OF ELECTRICAL POINTS
IF THE ELECTRICIANS FIX THE ELECTRCAL POINTS AND BOARDS ARBITARILY, IT WILL PROVE INCONVINIENT TO THE USERS .
After practical studies of their requirements . some standards have been recommended for fixing the heights of various electrical points
TANDARD HEIGHTS OF ELECTRICAL POINTS FROM FINISHED FLOOR LEVEL SN
O
NAME OF POINT RECOMMENDED POSITIONS 1 Angle holder (bracket point ) 2.25m (7’6”) from FFL
2 Fan point On celing , centrally ay diagnols crossing of rooms
3 Switch board 1.35m (4’6”) from FFL 4 t. v / telephone and 5amp point 0.6m (2’0”) from FFL
5 Bell push 1.35m (4’6”) From FFL
6 DB (distribution box) Above the entrance door or in passage 2.4m (8’0”) from FFL
(3) SIZES OF BOARDS
Wooden switch boards for sur face mounting are usually available in standard sizes
SN
O TYPE OF BOARD SIZE IN MM SIZE IN INCH 1 Distribution board 350mm * 305mm 14” *12” 2 Switch board in living /
kitchen/bedroom 200mm * 250mm 8” * 10” 3 Switch board outside WC /bath 180mm * 100mm 7” * 4” 4 Switch board refrigerator in kitchen 155mm * 100mm 6” * 5”
5 Bell push 100mm * 100mm 4” *4”
6 Bracket light point and fan point 100mm diameter 4” 7 t.v / telephone socket 100mm * 100 mm 4” *4” 8 t.v electrical point 100mm * 100mm 4” * 4”
(4) GAUGES OF WIRE S
So, it is essential to know the current carrying capacity of the wire for safe working.
SNO TYPE AND
GAUGE OF WIRE SIZE OF WIRE AVAILABLE IN MARKET
SIZE OF WIRE IN
mm WEIGHT OF WIRE PER 100M
1 1/18 1/036 1/0.914 1.4kg 2 1/18 1/038 1/0.965 1.5kg 3 1/18 1/042 1/1.067 1.7kg 4 1/18 special 1/044 1/1.120 2.0kg TWISTED COPPER 5 3/22 3/029 3/0.737 2.2kg 6 3/20 3/032 3/0.813 2.4kg 7 3/20 3/034 3/0.864 2.7kg 8 3/20special 3/036 3/0.914 3.1kg 9 7/22 7/029 7/0.737 4.4kg 10 7/20 7/032 7/0.813 5.0kg 11 7/20 7/034 7/0.864 5.5kg 12 7/20 special 7/036 7/0.914 6.5kg 13 7/18 7/040 7/1.016 9.0kg 14 7/18 special 7/044 7/1.120 10.0kg P.V.C TO P.V.C (FOR C.T.S WIRING) 15 1/18 1/036 1/0.914 2.2Kg 16 1/18 1/042 1/1.067 2.8kg
17 3/20 3/034 3/0.864 3.8kg (5) SIZES OF WIRES FOR VARIOUS PURPOSES
(6) COLOR CODES OF WIRES IN SINGLE PHASE 1.PHASEWIRE RED, 2. NEUTRAL BLACK 3 EARTHING GREEN IN THREE PHASE 1.RED 2. YELLOW 3 BLUE 4. NEUTRA BLACK 5. EARTHING GREEN.
RECOMMENDED RATING OF SWITCH SOCKETS AND CABLE SIZE ARE AS FOLLOWS 1. LIGHT ELECTRIC LOADS LESS THAN 250W SUCH AS LAMPS TUBES RADIO
SWITCH / SOCKETS OUTLETS CAPACITY IS 5 AMPS SUGGESTED CORE SIZE OF COPPER CABLE IS 1.5 MMSQUARE
2. MEDIUM ELECTRIC LOAD BETWEEN 250W TO 1000W SUCH AS WASHING MACHING REFRIGERATOR ,IRON ETC IS SWICH /SOCKET OUTLET IS 2.5
MMSQUARE AND SUGGESTED CORE SIZE OF COPPER CABLE IS 2.5MMSQUARE 3. HEAVY ELECTRIC LOADS BETWEEN 1000W TO 3000W SUCH AS GEYSOR, AIR
CONDITIONERS ETC ALSO SUB DISTRIBUTION BOARD IS 15 AMPS SWITCH / SOCKET OUTLET AND SUGGESTED CORE SIZE OF COPPER CABLE4 MMSQUARE 4. SOPHISTICATED EQUIPMENT SUCH AS COMPUTER IS 5AMPS AND SUGGESTED
CORE SIZE OF COPPER CABLE IS 1,5 MMSQUARE
5. SPECIFIC EQUIPMENTS WORKING ON BATTERIESON MAIN POWER FAILURE SUCH AS FAX / ANSWERING MACHINE IS 15 AMPS AND SUGGESTED CORE SIZE OF COPPER CABLE IS 4.0 MMSQUARE
6. TELECOMMUNICATION EQUIPMENT LIKE TELEPHONE FAX ETC IS SWITCH SOCKET OUTLETS IS TELEPHONE WIRE AND SUGGESTED CORE SIZE OF COPPER CABLE IS 4 OR 6 CORE
7. SAFETY AND PROTECTION EQUIPMENT LIKE ALARMS ETC IS 5 AMPS AND SUGGESTD CORE SIZE OF COPPER CABLE IS 1.5 MMSQUARE.
PLANNING FOR EXTERNAL ELECTRICAL WORK
1. FLOW CHART FOR ELECTRIC SUPPLY FROM ELECTRICITY BOARD TO CONSUMER
TRANSFORMER
L . T ROOM
FEEDER PILL
BUS BAR OF EACH BUILDIN
INDIVIUAL METRE OF FLAT
CUT OUT / FUSES
MAIN SWITCH OF EACH FLAT IN METRE
CABINET
MAINS
DISTRIBUTION BOX IN FLAT
CIRCUITS
ROOM SWITCH BOARDS
INTERNAL WIRING
(2) TRANSFORMER AND L.T (LOW TENSION) ROOM
Loads above 50 kw require a transformer and L.T room . the following points should be considered while planning the location of the transformer place and L.T room
• Location of an electrical transformer / L.T room, for a group of buildings , should be at the nearest convenient place on the ground floor.
• The floor level of the transformer / low tension room shall be above the highest flood level of the locality
• The availability of nearby power lines may also be kept in view while deciding the location of the transformer / low tension room
• In the L. T room , provision for cable trench , for passing cables from the transformer room should be provided
• Plinth for the transformer should be constructed in rubble masonry , at the required height and side.
• The capacity of the transformer depends upon the load of the building
• The load should be calculated from the electrical points in each flat and each building
(3) FEEDER PILLAR
• Feeder pillar is a distribution box. It is generally fixed in common convenient place . the cable from the main supply board (L.T room) comes in the feeder pillar and is distributed to various outgoing and other points of supply
• Feeder pillar should be fixed on a firm concrete platform
• Feeder pillar should be painted in red and marking of the building number for feeder pillar should always be intact
• Feeder pillars are available in 200 , 400 , 600 and 1000amp capacity
• Bus – bar is a distribution box which provides tappings to different electrical metres
• The main supply to bus bar is provided from the feeder pillar by suitable cable
• Bus bars are available in 100 , 200 , 400 amp capacity
(5) ELECTRICALMETER CABINET
• Meter cabinet is required to contain the meters of each building
• Generally , meter cabinet is made of a wooden frame , covered with wooden shutters and weld mesh . for proper ventilation , meter cabinet should be located near the entrance of the building . this also allows easy access for the readings.
• Meter box should be fixed above 45 cm( 1’6”) from the floor level
• Size of the meter box should be decided as per the number of metres to be fixed
• For one meter about 0.28sq.m (3sft) space is required to accommodate fuse , main switch and the meter
• Meter cabinet should always be locked to prevent any mishaps
• All the meters in the cabinet should display the correct name and the flat number , for easy maintenance
• Wiring in the meter box should be safe and done properly , with the required size and colour codes of the wires
• Building number should be painted on the bus bar in the meter box
• M.C.B should be provided for every electrical meter
• Meter cabinet should be painted with primer and oil paint to avoid decay and termite attack
SR
NO DESCRIPTION LIGHT POINT FAN POIN T POWE R POINT BATH POWE R POINT PLUG PLUG ON BOAR D IND POIN T BELLPOIN T 01 ELECTRICAL POINTS 9 3 1 1 3 1 1 02 LOAD ON EACH POINT 40W 60W 500W 1500W 100W 100 W 100W 03 TOTAL LOAD IN WATT(W) 360W 180 W 500W 1500W 300W 100 W 100W 04 GRAND TOTAL LOAD 3040 SAY 3000W=3K W
NOTE; GEYSER OF 1500WATT IS CONSIDERED WHILE WORKING OUT LOAD.
FOR 14 FLATS ---3KW * 14 = 42KW FOR COMMON LIGHTS---2KW*1 = 2KW FOR PUMPS---6KW*1 = 6KW __________ 50KW
CURRENT CARRYING CAPACITY = 50*2.84 AMPS/KW = 142 AMPS (2.84 AMPS /KW CONSIDERING 0.8 AS POWER FACTORS)
NET CURRENT---= 142*0.75 (DIVERSITY FACTOR) = 106.5 AMPS
TOTAL NET CURRENT REQUIRED IS 106.5 AMPS FOR BUILDING ON 3 PHASE, 31/2 CORE CABLE.
________ = _________ ROOT 3 1.732
= 61.56 AMPS (SAY 62 AMPS)
P= VI COS &
THREE PHASE SUPPLY P= ROOT 3 VI COS&.
(7)EARTHING
• Earthing is the term used for the electrical connection to the general mass of earth
• There are various methods of earthing but the most common method is earthing by plate electrodes
• Plate electrodes are made of copper or galvanized iron
• The size of copper plate shall not be less than 600mm * 600mm* 3.15mm and the thickness of the iron plate should not be less than 6.30mm
• Earthing plate should be placed vertically on its edge
• The top edge of the plate should not be less than 1.5m below the surface of the` ground
• Resistance of the earth electrodes depends upon the resistance of the soil
PROCEDURE OF EARTHING
• Dig a pit of size 90cm * 90cm * 90cm , 1.5cm below the ground
• Put a 15 cm layer of charcoal and salt to reduce the resistance of the soil
• Tie the copper wire / galvanized iron wire to the earthing plate and put the plate In the pit
• Size of the wire should not be less than 3sqmm in case of copper wire and 6sqmm . in case of G.I wire . fix a funnel from the pit to the ground level to pour water , to maintain a safe value of earth resistance. The earth resistance value should not exceed 0.7ohms
• Provide another G.I pipes of 25mm diameter to pass the earth wire upto and above ground level
• Fill the pit (90cm*90cm*90cm) with charcoal and salt , 40kg each. Refill the balance pit with soil and compact it properly
(7)CABLING AND DUCTING
• Once the location of the transformer , L.T room feeder pillar , meter cabinets etc. are finalized , decide on the cabling ducting
• Most of the cables are laid under ground in conduits
• In case of a cable without conduits , lay it carefully . ensure a brick layer and sand cushion, with an excavation of minimum 1m depth
• A chamber should be provided at each junction and turning . it should be covered properly about 15cm (6”) from the ground level , to prevent mud and water from entering.
(8) CONSTRUCTION QUALITY IN ELECTRICAL WORKS.
To follow IS specifications to cover various items internal electrification fittings and code of practice for execution IE rules 1956
IS732 ; code of practice for electrical wiring installation, having part 1,2,3, which cover definitions and general requirements design and construction, inspection and testing of installations
IS4648 guide lines for layouts in residential buildings
IS 694; PVC insulated cables for working voltages upto including1100 volts
(9)ELECTRICAL LOADING OF FITTINGS
3HP to 5 HP 416 volts 3 phase ( 8 amps ) cable size 3 core 4 mm2 ton to 1.5 ton AC 240 V single phase (10 Amps) cable size 3 core 4 mm2
light incandes cent 40, 60 Watt ,fluorescent 40W kitchen fan 50W
ceiling fan 100W refrigerator 100W geyser 1500W Mixer 200W washing Machine 200W electric iron 500W
10) INSULATION RESISTANCE OF COMPLETE INSTALLATION WITH EARTHING
To ensure that the wires used are correct size quite sound now to avoid leakage the insulation resistance has to be checked keeping the main switch in off position with all fuses in distribution board and all lamps put in position and test is done with 500V megger . the measure resistance live conductor and neutral at the out going terminal of the main switch earth should not be less than 50 Mega ohms divided by no of points (fan ,light, sockets) it should be more than 1 Mega ohm
insulation resistance between conductors
keeping the main switch in off position with all fuses in distribution board in position with all lamps removed from holder the insulation resistance between phase and neutral conductor checked by 500V meggar should not be less than 1 Mega ohm
extract s of IE rules the following IE rules 1956 which are given at the end are to be read thoroughly and follow while executing and operating the installations chapter1B
rules 29,30,31,32,33,34,35,36,38,,40,,41,42,43,44,44A chapter5 rules 47,48,49,50,51,58, chapter6 rules 61,62, chapter7
rules 63,64,65,66,67,68,69, chapter 8
rules 74,75,76,77,78,79,80,81,82,83,84,85,86,87,88,89,90,91,92,93, some high lights of rules
rule 29 construction, installation, operation and maintenance of electric supply lines and application
1. all electric supply lines and apparatus has to be of sufficient ratings for power insulation and estimated fault current and of sufficient mechanical strength for duty which they may require to perform under the
environmental conditions of installation and shall be constructed,
installed , and protected, worked and maintained in such a manner as to ensure safety of human being , animal s and property
2. the material and apparatus used must conform to relevant specifications of BIS rules 30 service lines and apparatus on consumers premises
