This document provides information and safety guidelines for electrical work. It discusses checking for wires before cutting walls, obtaining certificates for work, turning off power when working on circuits. It also summarizes types of electrical equipment, how household electrical systems work with main units and consumer boxes distributing power, basic equations for calculating circuits, types of cables and flex, and guidelines for ring main and radial wiring circuits. Safety is emphasized throughout, including ensuring no accidental power restoration.

1. ELECTRICAL SAFETY
Checklist:
Overall safety
Equipments/Tools
How it works
Cables / Flex
Fuses

2. Safety
 Check all walls for wires and pipes
before cutting out for any new cables
and boxes. A detector (shown here) can
identify cables in the wall.
 If in any doubt whatever consult a
qualified electrician. There is a legal
requirement to obtain a completion
certificate from a qualified electrician,
for any work you do that requires a
mains connection.
 For any work within circuits a minor
works certificate should be obtained.

3. Safety –cont.
Turn off the 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.

4. Electrical Hazard!

5. Equipment / Tool
Plastic socket
plates
Plastic
switches
Stainless steel
sockets
Brass sockets
Insulating tape 2.5mm Twin and earth RCD sockets Timers

6. Equipment / Tool
Wire
strippers
Electrical
screwdrivers
Socket
testers
Electricians side
cutters
Cable detectors Junction boxes

7. 1000V Insulated
VDE
Screwdriver Set
7 Pc
33 Piece
Screwdriver Bit
Set
Analogue
Pocket
Multimeter
Builder's
Goldscrew
Trade Case
EuroPlus Basic
Assortment
Storage Boxes
Marbo 2G 25mm
Surface Pattress
Roughneck
Electricians'
Bolster 3"" x 11""
Site VDE
Diagonal/Side
Cutters 150mm
(6"")
Equipment / Tool

8. Equipment / Tool
Armeg Complete
Electricians
Installation Kit
Clipsal 13A 1G
Sw Skt
Polycarbonate
Clipsal 13A 2G
Sw Skt
Polycarbonate
Clipsal Converta
Skt 1G to 2G
Polycarbonate
Clipsal Converta
Skt 2G to 3G
Polycarbonate
NWS VDE Side
Cutters 160mm
(6¼"")
Plano
Electricians
Pouch
VDE Slip Stop
Screwdriver Set
7Pc

9. 1000V Insulated
VDE
Screwdriver Set
7 Pc
33 Piece
Screwdriver Bit
Set
Autoranging
Digital
Multimeter
Builder's
Goldscrew
Trade Case
Heavy-Duty
Wire Strippers
Roughneck
Electricians'
Bolster & Guard
3"" x 11""
Site VDE
Diagonal/Side
Cutters 150mm
(6"")
Site VDE Wire
Strippers
150mm (6"")
Equipment / Tool

10. How it works
 An electrical supply come
to your home at a main,
sealed fuse called a
service head.
 From there, it will go to
your meter via a pair of
large black wire.
 The meter measures how
much electricity you use.
At no time should you
touch either the service
head or the meter
(offence).
Main Unit

11.  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 works – cont.

12. Inside Consumer Unit
DO NOT MESS WITH THIS BOX!

13. Basic Equations
 The amount of electricity available to you is measured in
Volts (V), and the rate at which it flows along its conductors
is measured in amps (ampere, A). The power required by
any appliance is measured in Watts (W). The formula for
working out the correct cable and fuse is; Watts divided by
Volts 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

14. 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).

15. Cables
 Fixed wiring is done in cable. This consists of individual
conductors (wires) sheathed separately, by insulation to
prevent leakage.
 The wires are then jointly covered by the outer sheath.
The wires are colour coded, red for live, black for neutral
and green/yellow striped for earth. Modern cables are
sheathed 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.

16. Cables –cont.
 1.5mm2 is most common in lighting circuits.
When installed it must not exceed 110m in length
and carries a fuse rating of 5 amps. (6 amps if
used 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), but
lighting circuits are normally run independently on
each floor of your house.
 2.5mm2 (as above but larger) is usually used for
the installation of power sockets on a ring main.
The circuit uses a 30 amp fuse at the consumer
unit (32 with a MCB). Cable length must not
exceed 60m or 50m with an MCB.

17. Wiring Rules

18. Flex
 Flex, is simply flexible cable
and is used for connecting
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 connecting
cookers etc, but these are
generally run directly from
the consumer unit and
require a professional
electrician for their
installation.

19. How to choose a Flex?

20. Fuses
 Fuses are placed into a
circuit as a deliberate weak
point. If anything goes
wrong within your circuit,
the fuse will "blow" first.
 With the modern RCD
boxes, the trip switch will
go.
 BUT BEFORE YOU PUSH
IT BACK ON, LOCATE
THE REASON WHY IT
TRIPPED. Most of the time
it is because the circuit has
been overloaded or there is
an earth fault. If you are in
doubt contact an electrician.

21. RING MAIN WIRING
•
• In a ring main, a ring of wires are
In a ring main, a ring of wires are circling
circling your home, carrying the mains
your home, carrying the mains
electricity to sockets on the way. It gets the power from the co
electricity to sockets on the way. It gets the power from the consumer unit
nsumer unit and
and
delivers it to the sockets.
delivers it to the sockets.
•
• As both ends of the ring are connected to the same terminals at
As both ends of the ring are connected to the same terminals at the consumer unit,
the consumer unit,
the current runs in both directions imposing
the current runs in both directions imposing less of a load
less of a load on the cables.
on the cables.

22. 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, is
dangerous, so a ring main delivers power from both ends to keep
the 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.

23. A separate ring main is usually installed on
every floor of the house to make sure
things are kept safe.
A ring main uses 2.5mm2 cable (cross
sectional area) comprising of a live,
neutral and earth.
The floor area a ring main serves is also
governed (regulation). The maximum area
for a ring main is 100 square meters.
Ring Main – cont.

24.  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.

25. 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.

26. High Power Appliance
 Units or appliances which use a lot of power, like
cookers and showers must be installed on their
own circuits, so please check the appliances
you are considering using on your ring main.
 It is also a regulation that any socket which is
capable of being used to supply power outside
of the house is protected by an RCD.
 Most modern consumer units will provide this
protection but again it is vital that you get a
qualified electrician to check and approve any
installation you may consider.

27. 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 ring
main may serve and use. (refer to Wiring Rules
Table)

28.  The diagrammes below show how you can break
into a ring main with junction boxes to extend it.
 There is no set limit to the number of sockets on a
ring main as long as within the rules mentioned
above.
 Obviously you will not want to have surface cables
all over the place; so remember if you place new
cables in any floor, roof or ceiling void they must
not be covered in insulation which will make them
too hot and if they are buried in the wall they must
be in a protective conduit and only run vertically
from above or below the sockets.
 Socket and switch plates in plastic, stainless steel
and brass.
EXTENDING A RING MAIN –cont.

29.  The first image shows a simple ring main to
and from the consumer unit.

30.  The image below shows the main extended via 2
new 30 amp junction boxes.

31. RADIAL CIRCUIT WIRING
 A radial circuit is a mains power circuit found in some
homes to feed sockets and lighting points.
 Simply a length of appropriately rated cable feeding one
power point then going on to the next. The circuit
terminates with the last point on it.
 It does not return to the consumer unit or fuse box as
does the more popular circuit, the ring main.

32. RADIAL CIRCUIT –cont.
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 ring
main, spurs, or extra sockets, can be
added.
The number of spurs must not exceed the
number of existing sockets.

33. Spur Socket
 Very often we find we do not have enough
sockets at home. It is not a difficult job to add
another but there are certain rules to follow.
 A spur can be connected to an existing socket,
on either a ring main or a radial circuit, providing
that socket does not already have a spur.
 That is only one spur per socket is allowed and
the number of spurs must not exceed the
number of sockets.
 If this is necessary in any part of your home, the
only way you can do this is by adding another
ring main or by extending one of the ring mains
you have.

34. 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 you
only 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.

35. SPUR
• The cables to and from any
spurs you connect must be
protected by a conduit of some
kind; be it on the surface or
buried in the wall.
• If you bury cables in the wall
they must only run vertically,
not horizontally.
• Cables may be placed in floor
or ceiling voids but not
wrapped in, insulation where
they may become too hot.

36.  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.

37. TNB Bill
Exercise:
A resedential house in
Malaysia consumes 500 kWh
of electricity in Jan 2009.
Calculate the electricity bills
for 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