Electrical Work for Building Construction 66

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

LOCATIO N

PLUG POIN T

BELL POIN T

TV POIN T

TEL POIN T

-

PLUG ON BOAR D 1

1

Living room bedroom

1

1

1

1

1

-

1

-

-

-

-

1

1

1

1

-

-

-

-

1

--

-

-

-

-

-

-

1

-

-

-

-

-

-

-

6

Water closet Bathroom

1

-

1

-

-

-

-

-

7

Passage

1

-

-

-

-

-

-

-

2 3 4 5

LIGH T POIN T 2

FAN POIN T

POWE R POINT

1

2

Kitchen room Balcony

(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 1

NAME OF POINT

RECOMMENDED POSITIONS

Angle holder (bracket point )

2.25m (7’6”) from FFL

2

Fan point

3

Switch board

On celing , centrally ay diagnols crossing of rooms 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)

7

POWER POINT IN BATH

Above the entrance door or in passage 2.4m (8’0”) from FFL 1.5m (5’5”) from FFL

(3) SIZES OF BOARDS Wooden switch boards for sur face mounting are usually available in standard sizes SN O 1

TYPE OF BOARD

SIZE IN MM

SIZE IN INCH

Distribution board

350mm * 305mm

14” *12”

2

200mm * 250mm

8” * 10”

3

Switch board in living / kitchen/bedroom 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 Electrical wires directly carry the electrical current.

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 IN mm

WEIGHT OF WIRE PER 100M

1/18

SIZE OF WIRE AVAILABLE IN MARKET 1/036

1

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

ELECTRICITY BOARD

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 INDIVIUAL ELECTRIC POINT

(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

(4) BUS – BAR

•

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

•

Load and cable size calculation for one building of 14 flats (SPECIMEN)

SR NO

DESCRIPTIO N

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 FOR PUMPS------------------------6KW*1

= 2KW = 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. THERFORE CURRENT IN EACH PHASE 106.5

106.5

________

=

_________

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 ½ HP to 1HP ;

240 volts single phase (3.5 amps ) cable size 2 to 2.5 cm

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 50W

40, 60 Watt ,fluorescent

40W

kitchen fan

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

Thank You