An enclosure that contains different type of
switchgears, control and power units to perform
the desired operation.
Type of Panels
• PLC control panel
• Motor Control Centre (MCC)
• Relay Control Centre (RCC)
• Power Control Centre (PCC)
• Automatic Power Factor Control (APFC)
• Automatic Change Over Panel
• Low Tension (LT) Panel
• Medium Tension (MT) Panel
• High Tension (HT) Panel
• Extra High Tension (EHT) Panel
• Ultra High Tension (UHT) Panel, etc.
The apparatus used for switching, controlling
and protecting the electrical circuits and
equipment is known as switchgears.
Fuses, Circuit breakers, Relays etc.
A device which is used to open or close an
electrical circuit in a convenient way. It can
be used under full load or no load conditions
but it can’t interrupt the fault currents.
A fuse is a short piece of wire or thin strip
which melts when excessive current flows
through it for sufficient time.
It is inserted in series with the circuit to be
It works on the principle of Thermal property
Type of Fuses
High Rupturing Capacity (HRC)
Kit-Kat or Rewire able
Fuse materials are lead, tin, copper, zinc and
Current rating of fuse element: It is the maximum current
which the fuse element can normally carry without
overheating or melting.
Fusing current: It is the minimum current at which the fuse
Square of fusing current(I) =k × Cubed of diameter of the
wire(d); where k is fuse constant.
S.No. Material Value of k Value of k
d in cm d in mm
An equipment which can open or close a
circuit under no load, full load and fault
conditions. It is so designed that it can be
operated manually(or by remote control)
under normal conditions and automatically
under fault conditions. For the latter
operation, a relay circuit is used with a circuit
Type of Circuit-Breakers
• Miniature Circuit Breaker (MCB)
• Moulded Case Circuit Breaker (MCCB)
• Earth Leakage Circuit Breaker (ELCB)
• Residual Current Circuit Breaker (RCCB)
• Air Circuit Breaker (ACB)
• Vacuum Circuit Breaker (VCB)
• Oil Circuit Breaker (OCB)
• Sulphur Hexa Fluoride (SF6), etc.
In electrical power distribution, a bus bar is a strip of copper or
aluminum that conducts electricity within a switchboard,
distribution board, substation or other electrical apparatus.
Bus bar sizes can not be calculated only from overall size.
There are various derating factors like arrangement of
bus bar,nos of bus bar, spacing, enclosure size, ventilation
in room, temp rise, skin effect, proximity effect etc. which
need to be consider while designing the bus bar.
Generally current carrying capacity of Al. is 0.8A per sqmm
and Copper is 1.6A per Sqmm.
That does mean 1sqmm can carry 0.8 amp current .
If size of bus bar is 100mm x 10 mm then it can carry 800 amp.
Bus ways, or bus ducts, are long bus bars with a protective
cover. Rather than branching the main supply at one
location, they allow new circuits to branch off anywhere
along the route of the bus way.
It is used to reduce the amount of current sent to the
Ammeter for measurement.
A cable essentially consists of one or more conductors covered
with suitable insulation and surrounded by a protecting
Type of cables:
• Underground cable
a) Armoured cable
b) Unarmoured cable
• Overhead cable
Selection of cable:
1 sq.mm≈2 Amp.
Classification of Cables
Low-tension (L.T.) cables — up to 1000 V
High-tension (H.T.) cables — up to 11,000 V
Super-tension (S.T.) cables — from 22 kV to 33 kV
Extra high-tension (E.H.T.) cables — from 33 kV to 66 kV
Extra super voltage cables — beyond 132 kV
A cable may have one or more than one core depending
upon the type of service for which it is intended. It may be
(iv) four-core etc.
For a 3-phase service, either 3-single-core cables or
three-core cable can be used depending upon the operating
voltage and load demand.