Chapter 2 Lecture of EAT 105 PPKAS UniMAP.

1. Chapter 2: Final
Circuit & Load
Estimation

2. Definition of a final circuit
• A circuit connected directly to current using equipment, or to a
socket outlet or socket outlets or other points for the connection of
such equipment
• An outlet is defined as the termination of fixed wiring feeding a
luminaire, socket, or any current consuming appliance. From this it
will be seen that a final circuit might consist of a pair of 1.5mm2
cables feeding a few lights or a very 3 core cable feeding a large
motor direct from a circuit breaker or main switchboard.
• Socket outlet: A device, provided with female contacts, which is
intended to be installed with the fixed wiring, and intended to a
receive plug. A luminaire track system is not regarded as a socket
outlet system

3. Definition of a final circuit

4. Final Circuit Distribution
• Final circuits can be divided into the following types, all of which
will need different treatment when planning the size of the
conductors and the rating of the overcurrent devices:
The general of final circuits are:
1. Final circuit feeding fixed equipment or 2A sockets.
2. Final circuit feeding 13A sockets to BS 1363
3. Final circuit feeding sockets to BS 196 (5A, 15A, and
30A)
4. Final circuit feeding sockets to BS EN 60309-2 (industrial
types 16A, 32A, 63A and 125A)
5. Final circuit feeding fluorescent or types of discharge
lighting
6. Final circuit feeding motors
7. Final circuit feeding cookers

5. Sockets

6. Final circuit feeding fixed equipment or 2A sockets
• the number of points supplied is limited by their aggregate
demand, as determined from Table 1
• No diversity is permitted
Point of utilisation of current using equipment Current demand to be assumed
a. Socket outlets other than 2A • Rated current
b. 2A socket outlets • At least 0.5A
c. Lighting outlet* • Current equivalent to the connected load, with
a minimum of 100W perlampholder
d. Electric clock, electric shaver supply unit,
shaver socket outlet (complying with BS
4573), bell transformer, and current using
equipment of a rating not greater than 5VA
• May be neglected
e. Household cooking appliance • The first 10A of the rated current plus 30% of
the reminder of the rated current plus 5A if a
socket outlet is incorporated in the control unit
f. All other stationary equipment • British Standard rated current, or normal
current

7. Final circuit feeding 13A sockets to BS 1363
• The main advantages of the 13A socket with
fused plug are that any appliance with a
loading not exceeding 3.12kW (13A at 240V)
may be connected with perfect safety to any
13A socket, and under certain conditions an
unlimited number of socket may be
connected to any one circuit
• One point which must be borne in mind by
the designer is the question of the use of
outdoor equipment.
• 13A socket outlets circuits can be fed by
either radial or ring circuits.

8. Final circuit feeding 13A sockets to BS 1363
(Radial circuit arrangement)

9. Final circuit feeding 13A sockets to BS 1363
(Ring circuit arrangement)
• A ring circuits utilises one additional conductor to loop back to the
sending end. In other words, the socket outlets in the ring circuit
are fed by two parallel conductors.
• The sharing of the load between the two parallel conductors will
depend on the load distribution within the ring.

10. Final circuit feeding 13A sockets to BS 1363
• Recommendations exist in the IEE On Site Guide for standard
circuit arrangements with 13A sockets. These permit 13A
sockets to be wired on the final circuits as follows (subject to
any derating factors for ambient temperature, grouping or
voltage drop):
a. An unlimited number of socket outlets connected to a
final circuit serving a floor area not exceeding 100m2
wired with 2.5mm2 PVC insulated cables in the form of a
ring (or 1.5mm2 MI cables in the form of a ring), and
protected by 30A or 32A overcurrent protective device. In
actual practice, 10 number of socket outlets connected to
a final circuit wired with 2.5mm2 PVC insulated cables in
the form of a ring.

11. Final circuit feeding 13A sockets to BS 1363
b. An unlimited number of socket outlets connected to a final circuit
serving in floor area not exceeding 50m2 with 4mm2 PVC
insulated cables on a radial circuit (or 2.5mm2 MI cables on a
radial circuit) and protected by an overcurrent device of 30A or
32A rating.
c. An unlimited number of sockets connected to a final circuit
serving a floor area not exceeding 20m2 with 2.5mm2 PVC
insulated cables on a radial circuit (or 1.5mm2 MI cables on a
radial circuit) and protected by an overcurrent device not
exceeding 20A.

12. Malaysia Practices for 13A Socket Outlet (BS 1363)
Types of 13A Socket Outlets Area Malaysia Practices
Size of wires Fuse/Circuit
Breaker
Rating
1. Single socket outlet 20m2 • 2.5mm2 PVC
cables
16A
2. Double socket outlet 20m2 • 2.5mm2 PVC
cables
20A
3. Ring (10 Nos 13A
socket outlet provided
they are all located
within an area of not
more than 1000 sq feet)
100m2 • 2.5mm2 PVC
cables
32A
4. Radial (Max 6 Socket
Outlets)
50m2 • 4mm2 PVC
cables
32A

13. Final circuit for socket outlets to BS 196
(537-05, 553-01 & 553-02)
• These are industrial type sockets and
plugs, made three size, 5A, 15A and
30A with a maximum voltage of 250V.
As these sockets may be used for any
voltage up to 250V they must be
marked with voltage and current. By a
system of keyways the plug of a given
voltage cannot be inserted into a
socket of a different voltage. Quite a
large selection of supply voltages from
6V to 250V are catered for by this
system of keyways. All sockets are 2
poles with a scraping earth, and the
plugs are reversible.
• Plugs can be fitted with single pole or
double pole fuses made to BS 1361 for
fuses in the body of the plug, or to BS
196 for plugs with fused pins.

14. Final circuit for socket outlets to BS EN 60309-2

15. • Diversity factor, DF is the ratio of the sum of the maximum power
demands of the subdivisions, parts of a system, to the maximum
demand of the whole system or part of the system under
consideration.
Diversity Factor
IEE ON SITE GUIDE DIVERSITY FACTOR

16. • Maximum demand (often referred to as MD) is the largest current
normally carried by circuits, switches and protective devices; it does
not include the levels of current flowing under overload or short
circuit conditions
Maximum Demand
( ) (DF)FactorDiversityxCLLoadConnectedMDDemand,Maximum =