1. Consumer’s Main Switchroom & Main L.V. Switchboard
Learning outcome from this topic, the student is able to
state the functions and requirements of a main switchroom
state the functions and requirements of a main switchboard
sketch a single-line LV supply diagram from a main switchboard to different parts of a building
describe different tests for a switchboard (the type tests and routine tests)

2. Consumer’s Main Switchroom
General requirements for main switchroom
Sufficient space for work and to house the main switchboard and other distribution equipment (600mm for switchgear ≤ 100A, 900mm for those >100A)
Next to transformer room
Supply taking from a LV network, the room should be at the building entrance
Clear access
Good ventilation
Minimum illumination: Floor – 150 lx, wall: 120 lx
No water or drainage pipes inside

3. Consumer’s Main Switchroom
Function of a main switchroom
power is taken from a transformer room
power distribution to different parts of a building and for different usages
separate the consumer side from the power company

4. Layout of cubicle-type main switchboard
Components in a main switchboard
Body built with 2 mm-thick steel and coated with suitable paint
A busbar compartment with hard drawn copper and high conductivity to BS1432 or BS1433
Compartment for the incoming and outgoing cables
Neat internal wiring and with sufficient clearance
A compartment housing ACB, MCCB, fuseswitch, motor starter, capacitor bank, auto-changeover switch
A meter compartment to show the energy consumption or maximum demand

5. Layout of cubicle-type main switchboard
Components in a main switchboard
Measuring CTs and protection CTs
Meters showing current, voltage, power factor (and max. demand), etc. Now A digital multi-purpose is used for all
IDMT relays for overcurrent and earth-fault protection (Now a digital relay)
Charger and battery for closing/tripping of ACBs
Phase indication lamps
Anti-condensation heaters
Spare compartments

6. Layout of cubicle-type main switchboard
The main switch in a switchboard
For three-phase 4-wire supply, a triple-pole & neutral (TP&N) main switch (or circuit breaker) is used
The TP&N switch should interrupt all the phase conductors (R/Y/B)
A link (fixed by bolts or screws) should be inserted in the neutral conductor
For single-phase installations, a double-pole (DP) main switch should be used

7. Layout of cubicle-type main switchboard
If the supply is taken directly from a transformer room, the main incoming ACB
should be of draw-out type
should have a breaking capacity at least 40 kA
should be equipped with overcurrent & earth-fault protective relays
For an overall installation serving more than one building, the installation in each building should be treated as a separate installation. Each building should have a main switch.

8. Load Distribution in a Building
Refer to slide 10 for illustration
Tenant Supply Board
Connection to a transformer
Main incoming circuit breaker (ACB/MCCB) for overload and fault protections to the whole installation
Busducts leading to different load centres in the building
Bus section switch interconnects adjacent busbar section
Non-essential Public Supply Board
Bus section for the power supply to public facilities
Plumbing and drainage pumps, passenger lifts, non-essential lighting, A/C plant and spares, etc
Cable risers to different loads in the building
Protective devices for cable overload protection

9. Load Distribution in a Building
Emergency Supply Board
Connection with an emergency generator / UPS
ACB, MCCB, fuseswitch for overload and / or fault protections to essential loads
Automatic changeover switch
Two mutually exclusive switches
Normal open (N/O)
Normal close (N/C)
Switch ON/OFF
Sprinkler pumps, hydrant / hose reel pumps, firemen’s lifts, emergency lighting and spares, etc
A single-line low voltage schematic for the power distribution to different loads in a building is shown on slide 11

10. A single-line LV schematics

11. L.V. Switchboard

12. Air Circuit Breaker (ACB)