Volume 8 – Mechanical and Electrical Services - Malaysia Geoportal

Chapter 7 ELECTRICAL SERVICES
7.3.5.2 Switchgears
The switchgears normally encountered are the ordinary lamp and socket outlet switches, isolators
fuse switches, switchfuse, circuit breakers, changeover switches and contactors.
Given below are some useful notes on the more commonly used protective and isolating devices.
a) Isolators - These are used for local isolation only. They are not used for
cable protection.
b) Switch fuse/ switch fuse- This is a single unit made up of an isolator in series with an
HRC fuse the HRC Fuse being retractable. It comes in both
SP & N and TP & N configurations with standard rating being
20A, 30A, 45A and 60A.
c) MCCB This is both an isolating as well as a protective device to
control loads above 100A to 400A
d) Air-circuit-breakers - These together with over-current and earth leakage relays
are used for busbar ratings of 400A and above. They are
expensive but efficient tripping devices.
MCBs and MCCBs are generally being introduced to replace h.r.c.fuses, switch fuses, and even air
circuit breakers on account of their compact size, ease of maintenance and neat appearance when
incorporated into cubicles.
The choice of circuit breaker must conform to the fault level designed for. The interrupting capacity
of the circuit breaker must be equal to or greater than the amount of fault current that can be
delivered at the point in the system where the breaker is applied. The amount of fault current
supplied by a system can be calculated at any point in the system.
The following interrupting capacities should be considered for the 240/415V system:-
Main Switch Board : 43 KA(31MVA) to 32 KA(23MVA)
SUB Switch Board : 22KA 916MVA) to 14 KA(10MVA)
Distribution Board : 10KA to 6 KA
7.3.6 Distribution Board
Distribution board normally is wall mounted type. It consists of isolating switchgears, final sub circuit
breakers for over current and earth leakage protection. The mounting height for a distribution board
shall be 2m measured from the floor to the underside of the distribution board.
7.3.7 Generator Set
7.3.7.1 Generator room selection and authority’s requirement
Siting of generator set room and layout of generator set are important as they affect the
performance of the equipment. Generator set room should have as many external walls as possible.
In any case it is not advisable to have less than 2 external walls.
The minimum clearance height of the generator set room should be given careful consideration
during planning stage. If the minimum clearance height is insufficient, the exhaust system may not
be able to be properly installed resulting in high back pressure. This affects the performance of the
generator set and increases the noise level as well.
March 2009 7-11