DOMESTIC WIRING

Domestic wiring is a safe,convenient,neat and simple way of bringing electrical power through cables,into our homes for domestic use. Have you seen an electronic printed circuit board(PCB)?see how neatly the connecting stripes are laid and holes made at various points on them for connecting components! Imagine those metallic stripes to be cables,how rowdy would the board look like. That idea was borrowed from house wiring. Conduit wiring went further to ensure that no cables is seen on the walls.

Types of wiring

Only four types of wiring would be discussed in this book namely:

Surface wiring

Half conduit wiring

Conduit wiring

Trunking

Surface wiring

In this type of domestic wiring cables are laid on walls and run inside the ceiling. Wooden boards are mounted at cable’s terminals to support electrical fittings. This method is seldom used nowadays.

Some domestic wiring tools Wiring instruments

Hammer ohmeter

Plumb bob ammeter

Tape rule voltmeter

Punch megger tester

Screwdrivers

Striper

Pliers

Cutter

Chisel

Bending spring (for producing elbow or bend) in pipes

Fishing tape (for drawing in wire/cable into pipe)

Flame source (for heating PVC pipes when making elbow)

Pictures

Electrical symbols

Half conduit wiring

When cables are run through pipes buried in walls,deckings,floors and ceiling,it is called conduit wiring. In half conduit wiring pipes are buried only in walls but exposed cables run in ceiling. No cables are seen on walls or ceiling. Only circuit termination accessories like socket outlets,swiyches show evidence of wiring.

Half conduit wiring work begins after roofing before mounting of ceiling and plastering. Knock-out boxes with incorporated pipes are fixed at socket,switch and lamp positions. The wall is broken as wide and deep enough to accommodate the pipes and boxes. The top end of the wall is not broken to hold pipe in place. It is expected that the technician involved in conduit wiring should be equipped with skills on plastering or employ a bricklayer to tentatively plaster the broken parts of the wall after pipes have been laid.

Wiring materials

PVC pipe 20mm/25mm

PVC stop end box 20/25mm

PVC T-boxes 20/25mm

PVC U-box 20/25mm

PVC inspection box 20/25mm

Knock out box(single or double)

Distribution board

Earth leakage circuit breaker ELCB(single or three phase)

Running coupler 20/25mm

Male/female bush 20/25mm

Elbow bend:the elbow joint/bend can be obtained by buying the already made type or by bending pipe using spring. The later option is most preferable.

Making a bend

Insert the bending spring into the PVC pipe at the point to be bent. Hold the pipe with the required point over flame and turn it round so that the whole circumference is heated. When pipe is soft at that point,bend it to required angle and withdraw it from the flame. Allow it to cool an d then withdraw the bending spring.

Electric wires ranging from:1.0mm,1.5mm,2.5mm,4.0mm,6.0mm,10.mm,16mm etc

Single core,red,black&earth wire

1.5mm- lighting circuit

2.5mm ----13amps socket outlets

4.0mm---- 15amps socket outlets

6.0mm-----cooker control unit

16mm------service cable

Cut –out fuse and neutral link

Stages in half conduit wiring

1.marking out 2.piping 3.running wire into conduit pipe 4.connection/termination 5.testing.

Marking out

Marking out is the first thing to do after having the electrical design. It involves locating the socket outlets points,lighting including fans and distribution board etc here pipe routes are planned and how they connect all accessories

Piping

In this stage which is carried out before plastering,pipes are inserted/buried in walls. The pipes are connected to boxes situated at sockets and switches position. In half conduit wiring these pipes extend beyond the wall but are not run in the ceiling.

Pictures

Earthing

In swampy area the soil has more water content and so has low resistance unlike in the dry soiled Northern part of Nigeria where soil resistance is high. Resistance-reducing agent like charcoal and salt are used in earthing.

Dig the soil to a depth,pour in charcoal and some amount of salt,then place the earth rod in the hole and hammer it in till it is few centimeters below soil level. Carry out earth test test.

Picture

Connect the black probe of the megger tester to the clamp on the earth rod and short the red probe on the megger. Set megger to earthing test and switch it on. A low reading of less than 10.0 ohms indicates a good earth. A reading of 0 ohms is the best earth reading.

Connect the earthing wire to the clamp and bury the earth rod. The unit earthing wire from earthing point to the consumer earthing continuity conductor(ELCB) and remote end of every copper or aluminium earth-continuity conductor should not exceed 1ohm.

Domestic wiring

In full conduit wiring,pipes are run in walls, ceilings,decking and floor. No cable/wires are expected to be flying even in ceiling. Because of the nature of pipe networking in full conduit wiring,there are some materials used which are not needed in half conduit wiring. A loop-in box enables four pipes to be linked at a point. Elbow/bend are needed in full conduit wiring.

Types of connections

Pictures

Piping

Piping is not as easy as seen. A room may have 2way switches,fans,2gang switch for wall brackets and toilet fittings. The pipes networking needs planning to ensure there is piping in every wire route.

Pictures

Running wire into pipes

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There are some storey buildings that may not require conduit pipes to be buried inside the casted decking but pipes that convey wires could be suspended inside the ceiling under the casted decking as shown below.

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Trunking

If a building has already been plastered before one is called for wiring,breaking of the walls to bury pipes for conduit wiring may not be necessary. A surface conduit using pipes or trunking could be used. It is mostly used where additional circuit is required in an existing conduit wiring. However, if the surface conduit is to be carried out with pipes,saddle clips should be used to hold the pipes to the walls.PVC trunks can be opened at one surface so that through the surface concrete nails can be used to fasten the main trunk to the wall. Wires are then run in the trunk easily without use of fishing tape and the detachable piece carefully clipped onto the main trunk to cover the wires, giving a very tidy wiring. This is why trunking is most preferable to surface conduit wiring.

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PVC trunks are of different sizes in millimeters. The size and number of cables/wires determines the size of trunk selected for a particular job. The size is written on the trunk in this form 30x30x2700. This is a trunk of 30millimetre widwness,30millimetre depth and 2700millimetre length.

The common sizes of trunk available are:

16mmx16mmx2700mm

16mmx25mmx2700mm

25mmx25mmx2700mm

25mmx40mmx2700mm

40mmx40mmx2700mm

40mmx100mmx2700mm

100mmx100mmx2700mm

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Servicing a domestic building

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3phase supply to a storey building comprising of 2-three bedroom flat each in upper and ground floor.

The pattern or system of powering the building depend on cost implication,but the best practice is to have a bus-bar distribution board installed either in the ground or upper floor,but likely in ground floor for easy access. Although the rating of such bus-bar vary with the load estimated for the whole building as calculated in the load schematic table. Mostly,and from experience,for such a building 200amps bus-bar DB will be suitable and it is to be powered with 25mm armoured cable or 25mm copper conductor service cable.

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Table for conductor size and current: for fusing.

Items required for wiring the building

Bedrooms

13amps sockets-----------2

15amps socket------------1

60watts wall brackets-----3

60 watts centre light-------1 x 3 bedrooms

Fan and fan regulator--------1

Water heater switch--------1

Ceiling rose-------------------1

Lamp holder----------------1

2-way switch for centre light------------2

2gang switch for wall brackets and toilet lamp-------------1

Toilets

Water heater connector-------------1

Screw head fitting---------------------1 x 3 toilets

Living room

13amps sockets--------------------4

15amps socket---------------------1

Wall brackets-----------------------4

4ft fluorescent fitting--------------2

Fan and fan regulators--------------2

2-way switch------------------------3

3gang switch------------------------1

Ceiling rose--------------------------4

Dinning room

13amps sockets---------------1

15amps socket---------------1

Wall brackets-----------------3

Fan and fan regulator--------1

4ft fluorescent fitting----------1

2gang switch--------------------1

Ceiling rose----------------------2

Kitchen

Cooker control unit--------------1

13amps socket-------------------2

15amps socket-------------------1

Fan and fan regulator-----------1

4ft fluorescent--------------------1

2gang switch-----------------------1

Ceiling rose------------------------2

Verandah

4ft fluorescent fitting--------------1

Ceiling rose---------------------------1

Store

2ft fluorescent fittings-----------------1

1gang switch------------------------1

Ceiling rose-----------------------1

Lobby

13amps socket ------------------1

2-way switch----------------------1

1gang switch----------------------1

Screw head fitting-----------------1

Passage

Distribution Board-----------1

ELCB-----------------------------1

Screw head fitting------------1

2-way switch------------------1

2gang switch------------------1

Entrance

Change-over switch---------1

Cut-out fuse-------------------1

Security

Bulkhead fitting--------------5

185mm earth rod and clamps

Table for the DB plan

s/no

Sub-circuit No MCB rating

Cable size Number of DB way

1 Cooker control unit 1 30A 6.0mm 12 15 amps sockets 6 20A 4.0mm 63 Water heater 3 20A 4.0mm 34 13 amps sockets for 2 bedrooms and lobby 5 20A 2.5mm 15 13amps sockets for a bedroom and kitchen 4 20A 2.5mm 16 13amps sockets for living and dinning rooms 5 20A 2.5mm 17 Lighting point for 2 bedrooms 10 5A 1.5mm 18 Lighting point for living room,dinning room and

entrance12 5A 1.5mm 1

9 Lighting point for lobby,passage and security light 7 5A 1.5mm 110 Lighting point for bedroom and kitchen 7 5A 1.5mm 1

Total 17

Requirement for piping process

Bedroom:

(3x3 knock-out box-------------7, U box--------------3, stop-end box-----------------------1) x3

Living room:

3x3 knock-out box-------------9, U-box--------------4, stop end box--------------2

Dinning room:

3x3 knock out box---------------3, U-box---------------3, stop-end box--------------1

Kitchen:

6x6 knock-out box-----------1, 3x3 knock-out box--------4, stop-end box-------1

Store:

3x3 knock out box-------------1

Lobby:

3x3 knock-out box------------3

Passage:

3x3 knock out box-----------2

Security:

U-box------------------4, stop-end box--------------------1

Others:

Bundle of PVC pipe 25mm--------------------------------1

Bundle of PVC pipe 20mm----------------------------------1

Meter board

Stablock fuses

Roll of 1.5mm cable(twin)-------------------------------9

Roll of 2.5mm cable, 3 core ----------------------------4

Roll of 4.0mm cable (red, black and earth)----------5

Roll of 6.0mm cable (red, black and earth)-----------20yards each

Roll of 10.0mm cable--------------------------------2

Marking out

13amps socket: at 0.5metre from floor level mark a vertical line up the wall and a short horizontal line. The point where the lines meet is where you will break for the 3x3 knock-out box and break the wall along the vertical line for the pipe.

15amps socket and switches: the horizontal line is drawn at 1.6metre from floor level and the vertical line is drawn up the wall

Wall mounted bulbs: their horizontal lines are drawn very close to the ceiling; 1-2 blocks to the ceiling.

Piping

Bedrooms

In the bedroom at the point indicated for 13amps sockets on the plan, measure 0.5metre from the expected floor,break a space for a 3x3 knock-out box such that it sits properly and flushes with the surface of the wall. Break space for a 20mm PVC pipe up the wall.connect the pipe and the box using a male and female bushings. Place them in position in the wall and hold in place by pieces of bricks.when breaking tunnel for the pipe some part of the topmost block is not broken but its hole is exposed so that pipe can be passed through the hole up. This will definitely help in holding pipe in place. Do same for the second 13amps and 15amps sockets only that the 15amps socket is located at 1.6metre from the floor

At the point allocated for water heater switch,which is supposed to be the bed space break wall two 3x3 knock out boxes which are about 25cm apart and at 1.6 metre from floor level. Connect the pipes and boxes and fix them in the space. On one of the boxes(the box for water heater switch),two pipes are needed while only a 25mm pipe is required on the other box.

By the door,at 1.6metre from floor level,break wall for two 3x3 knock boxes and a stop end box but only a 25mm pipe. The pipe is connected on a 3x3 knock-out box while other boxes are linked to it horizontally using short pipes.

At wall bracket locations break wall for U-box each at about two blocks to the ceiling (although this depend on the number of blocks the building has after the lintel.use 25mm pipe on the boxes

Living room

In the living room at the location where two 13amps sockets stays side by side break wall for a 3x6 knock-out box and a 20mm pipe. Connect the pipe to the box and place them in position. Other 13amps are single use 3x3 knock out box and 20mm pipe each. The 15amps socket’s 3x3 knock-out box is located at 1.6metre from floor level

By the door break wall for two 3x3 boxes and two stop-end boxes and a 25mm pipe each on the 3x3knock-out boxes. Connect the boxes together horizontally using short pipes, incorporate the 25mm pipes and fix them in position in the wall. At the other end of the living room use a3x3box and 25mm pipe for each of the 2way switches

Locate U-boxes and 25mm pipes for the wall brackets as explained earlier.

Dining room

The 13amps, 15amps sockets and the wall brackets’boxes should be located as explained for bedrooms. At the point where the 2gang is indicated locate a 3x3 box using a 25mm pipe.

Kitchen

At the ccu, break wall at about 1metre for a 6x6 knock out box and use two pipes on the box.

Fix boxes and pipes for the 13amps and 15amps sockets as earlier explained

At the location for the switches use 3x3 boxes and 25mm pipes

Security

The security bulbs are located outside on the wall on the second block to the ceiling. Use U-boxes and 25mm pipes for the conduit work. At the most wet point around the building fix a stop-end box a last block to the soil, break wall up the wall to the ceiling. This is for the earth wire.

Lobby

There are 13amps socket, 2way switch and a 1gang switch at the lobby.break wall for each at the specified height using 20mm pipe for the socket and 25mm pipe for the switches.

Passage

The DB, ELCB and change-over switch are located at the passage. Use 3x3knock-out box for both ELCB and change-over and use 25mm pipe on each. The boxes are fixed beside the DB and interconnected as shown below. Connect as pipe as possible on knock-out points on the DB.

Entrance

Break wall and locate 3x3 knock-out box and 25mm pipe for the 2gang at the passage. Fix a 3x3 knock-out box and 25mm pipe at fuse location

Passing wire

Atleast two persons are needed for wire passing; a person passing the fishing tape through a box and another personnel collecting it in the ceiling and passing to another pipe or to the DB outlet pipes. The wires or cable to be passed are secured firmly on a hook at the tail end of the fishing tape

The 15amps sockets are independent of other circuits,so draw in 4.0mm cable from their boxes to the DB

In the kitchen, draw in 6.0mm wires (red,black and earth) through the 6x6 box to the DB

The water switches at bedpost is a double pole switch so live,neutral and earth wire must come to the switch. Pass 4.0mm wires through one of the pipes to the DB,pass another 4.0mm wires through the other pipe to the ceiling of the toilet. The ceiling at the toilet is perforated at a point close to the wall, pass the wires of reasonable length through the hole.

Pass 2.5mm cable through the 13amps boxes to the ceiling. The cables of the 13amps sockets that are grouped together as a DB way are connected in the ceiling and then passed to the DB

Loop the U-boxes for wall brackets in the bedrooms as well as those in the dining room using a red and black 1.5mm wires. Run 1.5mm wires(red and black) to loop three of the U-boxes for the security light. Also run 1.5mm wires(red and black) to link the remaining two U-boxes at the back of the building.

The wall brackets in the living room are grouped into two. Link the boxes in each group using red and black 1.5mm wires.

Dining room:

From the 3x3box by the door pass four red 1.5mm wires;one as live(common) to the DB, the other three as tripper wires for centre light,wall brackets and ceiling fan. black 1.5mm wires are used as neutral for centre light, one of the U-boxes and the fan. The black wires are connected together in the ceiling.

Kitchen

By the door close to the verandah pass two red 1.5mm wires through the 3x3 box; one wire as live the other as tripper for verandah light. At the other door pass three red 1.5mm wires through the 3x3 box; one as live,the other two wires as tripper for fluorescent and fan. Use black wire to give each final sub-circuit neutral.

Bedrooms

From the second 3x3 box by the bedpost pass a red 1.5mm wire and two travelers(special black wires).the red wire(common) goes to the centre light as tripper wire while the travelers goes to the 3x3 box for 2way switch by the door. Through another pipe by the door pass three red 1.5mm wires as live(common) and tripper wires for fan and toilet bulb. Use black 1.5mm wire to supply neutral to all final sub-circuits.

Living room

From a 3x3 box bearing a pipe pass two travelers and two red 1.5mm wires; one as live(common) the other as tripper wire for entrance light. The travelers goes to one of the other 3x3 box for 2way switch at the other opening to the living room from where a red 1.5mm wire as common is passed to the

fluorescent. Four red 1.5mm wires are passed from another box bearing a pipe,as tripper wires for the fans and the two groups of wall brackets. Pass neutral to each final sub-circuit using black 1.5mm wire.link the fluorescents with red and black wires.

Three phase DB plan

Question: Design the plan of a 3phase DB supplying a 4bedroom flat (each with its toilet) having 2 rooms self-contain as boys quarter. Ensure considerable balance of load among the phases.

Bedrooms

15amps socket----------------1

13amps socket----------------2 x4 bedrooms

60 watts wall bracket-------3

60 Spot light-------------------1

Toilet

1500 watts water heater---1

Ceiling mounted screw head fitting----1 x4 toilets

Living room

15amps socket--------------1

13amps socket---------------4

60 watts wall bracket--------3

60 watts spot light------------2

Dining room

15amps socket--------------1

13amps socket--------------1

60 watts wall bracket------3

60 watts spot light----------1

Kitchen

Cooker control unit------------1

15 amps socket------------------1

13amps socket--------------------3

60 watts spot light-------------2

Store

60 watts spot light------------1

Lobby

60watts spot light--------------1

13amps socket------------------1

Passage

60 watts spot light -------------1

Entrance

60 watts ceiling mounted screw head fitting----------1

Verandah

13amps socket --------------1

60 watts ceiling mounted screw head fitting------------1

Security

60 watts bulkhead fitting-----------------------------------6

Water heater switch for 2HP pumping machine-------1

Boys Quarters

Room

15amps socket------------------------------1

13amps socket--------------------------------2 x2 rooms

Wall bracket --------------------------3

Toilet

60 watts screw head fitting---------------1

1500 watts water Heater-----------------1

A table showing distribution of subcircuit into ways

S/N subcircuit Number Number of ways

1 Cooker control unit 1 1 way2 15amps sockets 9 9ways3 Water heater 7 7 ways4 13 amps sockets for living room and Dinning room 5 1 way5 13 amps sockets for 2 bedrooms and lobby 5 1 way6 13 amps sockets for 2 bedrooms and verandah 5 1 way7 13 amps sockets for kitchen 3 1 way8 13 amps sockets for boys quarter’s rooms 4 1 way9 Lighting point boys quarters 8 1 way10 Lighting point, security 8 1 way11 Lighting point, living room and entrance 6 1 way12 Lighting point, bedroom and toilet 5 1 way13 Lighting point, bedroom and toilet 5 1 way

14 Lighting point, bedroom and toilet 5 1 way15 Lighting point, bedroom and toilet 5 1 way16 Lighting point,kitchen,store and verandah and dinning room 8 1 way17 spare 1 way

TOTAL 31 WAYS

Load schematic table. phases

s/no

Circuit type Circuit outlet Accessories No R Y B MCBrating

Expectedload

1 Power circuit CCU Cooker unit 1 1 30A 6500W2 Power circuit Direct-on-line

starterPumping machine

1 1 20A 2Hp=1492W

3 Power circuit 15amps socket Rice cooker 1 1 20A 1500W4 Power circuit Water heater

switchToilet water heater

1 1 20A 1500W

5 Power circuit Water heater switch

Toilet water heater

1 1 20A 1500W

6 Power circuit Water heater switch

Toilet water heater

1 1 20A 1500W

7 Power circuit Water heater switch

Toilet water heater

1 1 20A 1500W

8 Power circuit Water heater Toilet water 1 1 20A 1500W

switch heater9 Power circuit Water heater

switchToilet water heater

1 1 20A 1500W

10 Powercircuit 15 amps socket Air-conditioner 1 1 20A 1.5Hp=1119W11 Power circuit 15amps socket Air-conditioner 1 1 20A 1119W12 Power circuit 15 amps socket Air-conditioner 1 1 20A 1119W13 Power circuit 15 amps socket Air-conditioner 1 1 20A 1119W14 Power circuit 15 amps socket Air-conditioner 1 1 20A 1119W15 Power circuit 15 amps socket Air-conditioner 1 1 20A 1119W16 Power circuit 15amps socket Air-conditioner 1 1 20A 1000W17 Power circuit 15amps socket Air-conditioner 1 1 20A 1000W18 Power circuit 13ampssockets 5 1 20A 1000W19 Power circuit 13amps sockets 3 1 20A 1000W20 Power circuit 13amps sockets 3 1 20A 1000W21 Power circuit 13amps sockets 4 1 20A 1000W22 Power circuit 13amps sockets Heaters and

freezer3 1 20A 2000W

23 Lighting point

Bulbs 5 1 5A 300W

24 Lighting point

Bulbs 5 1 5A 300W

25 Lighting point

Bulbs 8 1 5A 480W

26 Lighting point

Bulbs 8 1 5A 560W

27 Lighting point

Bulbs 5 1 5A 300W

28 Lighting point

Bulbs 5 1 5A 300W

29 Lighting point

Bulbs 6 1 5A 360W

30 Lighting point

Bulbs 8 1 5A 480W

31 Spare 1 10A32 Total 10 10 11 36504W33

Red phase carries more load than other phases

Red phase power=6500+1500+1119+1119+1000+300+300+300+300=12438watts

P=VIcosØ take cosØ to be 0.7

12438=220xIx0.7

12438=154x1

I=12438/154

I=80.77A, A DB of 36ways, 100A will be suitable for the building.