Volume 8 – Mechanical and Electrical Services - Malaysia Geoportal

Chapter 7 ELECTRICAL SERVICES
The TNB needs to know the expected power demand of the installation in order to lay a suitable
cable for the incoming supply. This can be dealt with using the maximum demand plus diversity
factor criteria together with the methods outlined in the section for estimating procedures. The
design of the final sub-circuits must be done in accordance with the IEE Regulations (control,
distribution and Excess Current Protection).
7.2.15 Circuit Breaker Rating
It helps a lot, however, to keep the following rules in mind:-
Circuit Size of Wire
No. of Point per Circuit
Rating
5A 1.5mm 2 8 Nos. of lighting or fan points or 1 Nos of 5A
15A 2.5mm 2 1 Nos. 13A switch socket outlet
20A 2.5mm 2 2 Nos 13A s/s/o
30A(ring) 2.5mm 2 10Nos 13A s/s/o provided they are all located
within an area of more than 1,000 sq. ft.
30A(radial) 4.0mm 2 6 Nos 13A s/s/o
A factor of 0.8 is normally applied to the specified rating of the distribution cable,i.e. not more than a
4A load on a 5A sub-circuit. This ensures that the circuit breaker rating is standard circuit breaker
Rating available.
7.2.16 Maximum Demand and Diversity Factor
The term maximum demand refers to the expected maximum power requirement of an installation.
This value is given by the product of the total connected load and the Diversity factor:
M.D. =T.C.L. x D.F.
Where:
M.D = Maximum Demand
T.C.L = Total Connected Load
D.F = Diversity Factor
Knowledge of this value enables TNB to determine the size of their incoming cable.
The total connected load is the load expected to be connected to the system while the diversity
factor is a weighting factor that is used to simulate actual loading conditions.
The IEE Regulations provides a table which enable one to estimate the maximum current which will
flow in an installation so as enable to calculate the size of cables, and switchgears. However, one
shall note that no diversity is to be allowed for when calculating the size of circuit conductors and
switchgear for final sub-circuit.
7.2.17 Schematic Drawing
For the design of schematic diagram, the power loading of both lighting and general power
requirement shall be calculated and planned. Typical single line diagram of a simple installation is as
shown in Appendix 7D.
7-8 March 2009