Guidelines for Schematic Diagram
ELECTRICAL INSTALLATION
Distribution Board
 Usually do not have metering scheme.
 Selection of MCCB based on TCL.
 Protection scheme: MCCB, MCB for final loads
 Leakage protection relay
 Chosen of leakage protection relay :
 Use ELR with Zct : 20A 3 phase ≤x ≤250A 3 phase
 Use EF with CT (min 2 OC/1EF) : x > 250A
 Installation of protection relay at:
 i. For isolators/mechanical loads: at upstream MCCB
 ii. For other type loads within same building: at downstream MCCB
 iii. Load via underground cable: at both upstream & downstream MCCB
Sub Switch board
 Consist of: Protection scheme
 Metering
 Protection scheme
 Circuit Breaker (based on calculation of MD)
 Leakage protection relay
Chosen of leakage protection relay :
Use ELR with Zct : 20A 3 phase ≤x ≤250A 3 phase
Use EF with CT (min 2 OC/1EF) : x > 250A
Installation of protection relay at:
i. For isolators/mechanical loads: at upstream MCCB
ii. For other type loads within same building: at
downstream MCCB
iii. Load via underground cable: at both upstream &
downstream MCCB
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 Metering
 The facility of measuring and monitoring devices at SSB is
depending to the incoming switch gear rating and the usage of
the panel. The items need to be installed are:
a) incoming phase indicating light – LED type c/w fuse
b) voltmeter
c) ammeter
d) kilowatt hour meter
e) items b, c and d may be replaced with a digital power meter to connect to
electrical building automation system (SCADA) enabling collecting data
and may be used for measurement of efficiency and improvement etc.
Main Switch Board
 Consist of: Protection scheme
 Metering
 Protection scheme
 Circuit Breaker (based on calculation of MD + 20%)
 Leakage protection relay
Chosen of leakage protection relay :
Use ELR with Zct : 20A 3 phase ≤x ≤250A 3 phase
Use EF with CT (min 2 OC/1EF) : x > 250A
Installation of protection relay at:
i. For isolators/mechanical loads: at upstream MCCB
ii. For other type loads within same building: at
downstream MCCB
iii. Load via underground cable: at both upstream &
downstream MCCB



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 Metering
 The facility of measuring and monitoring devices at SSB is
depending to the incoming switch gear rating and the usage of
the panel. The items need to be installed are:
a) incoming phase indicating light – LED type c/w fuse
b) voltmeter
c) ammeter
d) kilowatt hour meter
e) items b, c and d may be replaced with a digital power meter to connect to
electrical building automation system (SCADA) enabling collecting data
and may be used for measurement of efficiency and improvement etc.
 Name of MSB legend refers to the location of the panel.
 a) MSB NE (Non Essential)
 Supply direct from TNB
 b) MSB E (Essential)
 Supply from Generator Set
 c) MSB Mechanical, etc.
Example 1 – Main Switch Board
Incoming Normal Supply
Panel/Consumer HT Panel
 Sometimes two transformers are supplied by TNB. This may happen when:-
(i) a single transformer is insufficient to cater for the total load of the
installation, or
(ii) a more secured supply system for the installation is required.
 Whatever the cause may be, the main switchboard must be designed to receive
the two incoming feeders from the separate transformer.
 In this case it is normal practice to incorporate a 4 pole coupler between the
two sections of main busbars fed by the two transformers to provide further
flexibility in the supply system.
 The coupler must at least be mechanically interlocked with the other two
incoming Circuit Breaker (CB) so that the coupler can only be closed if either
one of the two incoming CBs is opened in order to satisfy TNB’s requirement.
 Consist of: Consumer’s HT panel
 TNB HT panel
 Consumer’s HT panel consists of: Metering
 Protection
Example 2 – Incoming Supply Panel
Concept of Breaker Sizing
Alternate Supply Panel
 Usually refer to Genset or UPS Panel
 Consists of: Protection scheme
 Metering
 Protection scheme: Air Circuit Brekaer
 Leakage Protection Relay
 Fine Surge Supressor
Load Assesment and Genset Sizing
 It is necessary to determine to which loads one proposes to
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maintain a supply under emergency conditions. These loads may
consist of static loads and motor loads.
The generator is sized with the main loads plus 20% on other
power requirements
such as lightings, small motors, etc.
Static load consist of lamps, communication equipment, etc. –
items which do not involve rotating machinery. Static loads are
expressed in kW.
Motor loads are those electrical motors which power such things
as fireman lifts, pressurization fans and fire fighting equipment.
These motor loads are also expressed in kW, but they also place an
additional demand on the electric supply.
 This demand is the starting kVA (skVA). The starting kVA for a
motor of 5 kW or more is 5.5 to 6 times the rated kVA and it is 8
to 10 times approximately in the case of one of 5 kW or lower.
 At starting, the motor normally apply a fairly large load to the
generator. Under the rated full load, most motors require about
1.4 kVA per kW. It is therefore easy to find out kVA values on the
basis of output kW.
 Thus to determine the total load,
a) Add up the static loads in kWto establish the total static load.
b) Identify the individual motor loads and compute their total kW
value.
c) Then individually calculate the starting kVA of each motor.
Automatic Main Failure Panel
 Make the power switch to emergency standby generators in
the event of a significant loss of mains power or total
blackout. Without AMF panels, generators need to be
operated manually and that can mean lost data, potential
damage to electrical equipment and huge amounts of
disruption
 Consists of: Phase indicator
 Interlock switch (contactor)
 Contactor size of AMF refers to nominal current of circuit breaker.
 Eg:- 800 A TPN of ACB follows 800 TPN 4 Pole Contactor of AMF.
Example 3 – AMF/Genset Control
Panel
Example 4 – Legend