KL1034 Lect2 Electrical wiring.pdf

7/27/2019 KL1034 Lect2 Electrical wiring.pdf

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ELECTRICAL SAFETY

Checklist:

Overall safety

Equipments/Tools

How it works

Cables / Flex

Fuses


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Safety

Check all walls for wires and pipesbefore cutting out for any new cablesand boxes. A detector (shown here) canidentify cables in the wall.

If in any doubt whateverconsult aqualified electrician. There is a legalrequirement to obtain a completioncertificate from a qualified electrician,for any work you do that requires amains connection.

For any work within circuits a minorworks certificate should be obtained.


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Safetycont.

Turn offthe power and remove the fuse

from any circuit you are working on.

Make sure no-one can turn the power on

by mistake.Use only approved materials and tools.


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Electrical Hazard!


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Equipment / Tool

Plastic socketplates

Plasticswitches

Stainless steelsockets Brass sockets

Insulating tape 2.5mm Twin and earth RCD sockets Timers


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Equipment / Tool

Wire

strippers

Electrical

screwdrivers

Socket

testers

Electricians side

cutters

Cable detectors Junction boxes


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1000V InsulatedVDEScrewdriver Set

7 Pc

33 PieceScrewdriver BitSet

AnaloguePocketMultimeter

Builder'sGoldscrewTrade Case

EuroPlus BasicAssortmentStorage Boxes

Marbo 2G 25mmSurface Pattress

RoughneckElectricians'Bolster 3"" x 11""

Site VDEDiagonal/SideCutters 150mm(6"")

Equipment / Tool


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Equipment / Tool

Armeg CompleteElectriciansInstallation Kit

Clipsal 13A 1GSw SktPolycarbonate

Clipsal 13A 2GSw SktPolycarbonate

Clipsal ConvertaSkt 1G to 2GPolycarbonate

Clipsal ConvertaSkt 2G to 3GPolycarbonate

NWS VDE SideCutters 160mm(6"")

PlanoElectriciansPouch

VDE Slip StopScrewdriver Set7Pc


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1000V InsulatedVDE

Screwdriver Set7 Pc

33 PieceScrewdriver Bit

Set

AutorangingDigital

Multimeter

Builder'sGoldscrew

Trade Case

Heavy-DutyWire Strippers RoughneckElectricians'Bolster & Guard3"" x 11""

Site VDEDiagonal/SideCutters 150mm(6"")

Site VDE WireStrippers150mm (6"")

Equipment / Tool


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How it works

An electrical supply cometo your home at a main,sealed fuse called aservice head.

From there, it will go toyour meter via a pair oflarge black wire.

The meter measures howmuch electricity you use.

At no time should youtouch either the servicehead or the meter(offence).

Main Unit


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From main unit, the

electricity will go to your

consumer unit, from

where it is distributed

around the house. Each circuit is fused at

this box either by an

amp rated fuse wire, or

a trip switch if you

have an RCD (Residual

Current Device).

How it workscont.


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Inside Consumer Unit

DO NOT MESS WITH THIS BOX!


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Basic Equations

The amount of electricity available to you is measured inVolts (V), and the rate at which it flows along its conductorsis measured in amps (ampere, A). The power required byany appliance is measured in Watts (W). The formula forworking out the correct cable and fuse is; Watts divided byVolts equals Amps .

P = VI Or, I = P/V

And, V =IR

So, P = VI = V(V/R) = V2/R

Or P = VI = (IR)I = I2R Maximum power that can be served by a socket adapter

(multiple slot);

P = VI = 240 V x 13 A = 3120 Watts

Where I = fuse rating in the adapter


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Electrical Circuit

Electricity flows along the live (red) wire,feeding whatever is required and then returns

along the neutral wire to the consumer unit

(supply).

The flow can be stopped by the insertion of a

switch, which is placed in the live wire.

Switches, most often, will be linked from

your ceiling rose through a separate cable,

even though one of the wires in this cable is

black it is still live.

For a switch, 2 wires are ALIVE, i.e red

(coming in) and black (going out).


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Cables

Fixed wiring is done in cable. This consists of individualconductors (wires) sheathed separately, by insulation toprevent leakage.

The wires are then jointly covered by the outer sheath.The wires are colour coded, red for live, black for neutraland green/yellow striped for earth. Modern cables aresheathed with PVC which has an indefinite life, older

cables were rubber with about 20/30 years life. If your home has these cables do not attempt electrical

extensions with them.


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Cablescont.

1.5mm2 is most common in lighting circuits.When installed it must not exceed 110m in lengthand carries a fuse rating of5 amps. (6 amps ifused in conjunction with a miniature circuit breaker,MCB). It is acceptable to run 1200 Watts on this

cable, (equivalent of 12 x 100 Watt bulbs), butlighting circuits are normally run independently oneach floor of your house.

2.5mm2 (as above but larger) is usually used forthe installation ofpower sockets on a ring main.

The circuit uses a 30 amp fuse at the consumerunit (32 with a MCB). Cable length must notexceed 60m or 50m with an MCB.


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Wiring Rules


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Flex Flex, is simply flexible cable

and is used forconnecting

appliances. The colour

coding is different using

brown for live, blue for

neutral and green/yellow

stripes for earth.

There are many more

cables for connectingcookers etc, but these are

generally run directly from

the consumer unit andrequire a professional

electrician for their

installation.


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How to choose a Flex?


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Fuses

Fuses are placed into acircuit as a deliberate weakpoint. If anything goeswrong within your circuit,the fuse will "blow" first.

With the modern RCD

boxes, the trip switch willgo.

BUT BEFORE YOU PUSHIT BACK ON, LOCATETHE REASON WHY ITTRIPPED. Most of the timeit is because the circuit hasbeen overloaded or there isan earth fault. If you are indoubt contact an electrician.


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RING MAIN WIRING

In a ring main, a ring of wires areIn a ring main, a ring of wires are circlingcircling your home, carrying the mainsyour home, carrying the mains

electricity to sockets on the way. It gets the power from the coelectricity to sockets on the way. It gets the power from the consumer unitnsumer unit andand

delivers it to the sockets.delivers it to the sockets.

As both ends of the ring are connected to the same terminals atAs both ends of the ring are connected to the same terminals at the consumer unit,the consumer unit,

the current runs in both directions imposingthe current runs in both directions imposing less of a loadless of a load on the cables.on the cables.


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Ring Main Electricity loses power over long lengths of cable and trying to put

too much power through a cable which is not designed for it, isdangerous, so a ring main delivers power from both ends to keepthe load as light as possible.

The back of a socket on a ring main looks like this.

The other type of circuit used to power your home is a radial circuit.There are not so common and can easily be turned into a ring

circuit.


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An average house has a footprint of about 64-70

square meters so this allows for the continuation

of the ring into a porch or garage etc.

The ring main must be protected by a 30 amp

fuse if it is on a cartridge fuse board, or a 32

amp MCB fuse.

The cable itself can be up to 60 meters long if it

is protected by a cartridge fuse and 50 meters

long if protected by an MCB.

Ring Main cont.


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There is no limit to the number of sockets you can have on a ring

main but there is a limit to the number of spurs you can have from

those sockets or from the wiring between them.

See next section on adding an extra socket. You can also extend

the ring main if you need to.


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High Power Appliance

Units or appliances which use a lot of power, likecookers and showers must be installed on theirown circuits, so please check the appliancesyou are considering using on your ring main.

It is also a regulation that any socket which iscapable of being used to supply power outsideof the house is protected by an RCD.

Most modern consumer units will provide thisprotection but again it is vital that you get a

qualified electrician to check and approve anyinstallation you may consider.


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EXTENDING A RING MAIN

Summary: Extending a ring main. Adding

sockets to a ring main. Putting more sockets in a

room or office.

If you need extra sockets in a new room or turn

an old room into an office, it may not be possible

to add extra sockets from your existing ring main.

It is not particularly difficult to extend a ring main

but you must remember that certain rules apply

about the floor area and length of cable one ringmain may serve and use. (refer to Wiring Rules

Table)


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The diagrammes below show how you can breakinto a ring main withjunction boxes to extend it.

There is no set limit to the number of sockets on aring main as long as within the rules mentionedabove.

Obviously you will not want to have surface cablesall over the place; so remember if you place newcables in any floor, roof or ceiling void they mustnot be covered in insulation which will make themtoo hot and if they are buried in the wall they mustbe in a protective conduit and only run verticallyfrom above or below the sockets.

Socket and switch plates in plastic, stainless steeland brass.

EXTENDING A RING MAINcont.


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The image below shows the main extended via 2

new 30 amp junction boxes.


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RADIAL CIRCUIT WIRING

A radial circuit is a mains power circuit found in somehomes to feed sockets and lighting points.

Simply a length of appropriately rated cable feeding onepower point then going on to the next. The circuitterminates with the last point on it.

It does not return to the consumer unit or fuse box asdoes the more popular circuit, the ring main.


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RADIAL CIRCUITcont.

The descriptions below apply only to a

circuit for power sockets.

There is no limit to the number of sockets

used on a radial circuit and, just like a ringmain, spurs, or extra sockets, can be

added.

The number of spurs must not exceed the

number of existing sockets.


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Spur cont.

The spur must be connected to the

existing circuit using the same cable as

used in the main circuit.

A general rule for a ring main is that if youonly have two cables in the back of an

existing socket then it is ok to spur.

If there are 3 cables coming out of any

socket then it is NOT OK to spur.


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A spur can be added to any part of the circuit providing

the rules above are followed. If there is not an existing

socket near enough, you can connect into the cable by

means of a junction box for your new spur.


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TNB Bill

Exercise:

A resedential house in

Malaysia consumes 500 kWh

of electricity in Jan 2009.

Calculate the electricity billsfor this house if the tariffs are

as follows:First 200 kWh @ RM 0.20/kWh

> 100 kWh @ RM 0.25/kWh

> 100 kWh @ RM 0.30/kWh

Documents

KL1034 Lect2 Electrical wiring.pdf