BUILDING SERVICES

1. FUSES

3. What is Fuses?
⚫ Afuse is a device that protects a circuit from an over
current condition.
⚫ It has a fusible link directly heated and destroyed by
the current passing through it.
⚫ A fuse contains a current- carrying element sized so
that the heat generated by the flow of normal current
through it does not cause it to melt the element;
however, when an over current or short-circuit current
flows through the fuse, the fusible link will melt and
open the circuit.

4. Typesof Fuses
⚫ A fuse unit essentially consists of a metal fuse element or link, a
set of contacts between which it is fixed and a body to support and
isolate them.
⚫ Many types of fuses also have some means for extinguishing the
arc which appears when the fuse element melts.
⚫ In general, there are two categories of fuses.
1. Low voltage fuses.
2. High voltage fuses.

5. ⚫ Usually isolating switches are provided in series with
fuses where it is necessary to permit fuses to be
replaced or rewired with safety.
⚫ In absence of such isolation means, the fuses must be
so shielded as to protect the user against accidental
contact with the live metal when the fuse is being
inserted or removed.

6. (1) Re-Wirable Fuse /Kit-Kat fuse:
⚫ The most commonly used fuse in house wiring.
⚫ It consist of a porcelain base carrying the fixed contacts
to which the incoming and outgoing live or phase wires
are connected and a porcelain fuse carrier holding the
fuse element, consisting of one or more strands of fuse
wire, stretched between its terminals.
⚫ The fuse carrier is a separate part and can be taken out or
inserted in the base without risk, even without opening the main
switch.
⚫ If fuse holder or carrier gets damaged during use, it may be
replaced without replacing the complete unit.
⚫ The fuse wire may be of lead, tinned copper, aluminIum or an
alloy of tin lead.
⚫ The actual fusing current will be about twice the rated current.

7. Contd..

8. (2) Cartridges Type Fuse:
⚫ The fuse element is enclosed
in a totally enclosed container
and is provided with metal
contacts on both sides.
⚫ They are cylindrical in
shape and have a
contact point at each
end.
⚫ Cartridge fuses are
typically constructed
fro m ceramic, glass or
porcelain.

9. High Rupturing Capacity (HRC)
□
HRC fuse or high rupturing
capacity fuse– In that type of fuse,
the fuse wire or element can carry
short circuit heavy current for a
known time period.
□During this time if the fault gets
removed, then it does not blow off.
Otherwise, it blows off or melts.

10. EARTHING

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12. Electrical Earthing
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⚫ Definition: The process of transferring the immediate
discharge of the electrical energy directly to the earth by the
help of the low resistance wire is known as the electrical
earthing.
⚫ The electrical earthing is done by connecting the non-current
carrying part of the equipment or neutral of supply system to
the ground.
⚫ Mostly, the galvanised iron is used for the earthing.
⚫ The earthing provides the simple path to the leakage current.
⚫ The shortcircuit current of the equipment passes to the earth
which has zero potential.
⚫ Thus, protects the system and equipment from damage.

13. Importance of Earthing
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The earthing is essential because of the following reasons :
□The earthing protects the personnel from the shortcircuit current.
□To avoid electic shock
□The earthing provides easiest path to the flow of shortcircuit
current even after the failure of the insulation.
□The earthing protects the apparatus and personnel from the high
voltage surges and lightning discharge.
□To avoid isk of fire due to earth leakage current though unwanted
path

14. Methods of Earthing
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There are several methods of earthing like
⚫ wire or strip earthing,
⚫ rod earthing,
⚫ pipe earthing,
⚫ plate earthing or
Most commonly used methods of earthing are pipe earthing
and plate earthing.

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16. Plate
Earthing
⚫ In Plate Earthing an earthing
plate either of copper of
dimension 60cm×60cm×3m of
galvanized iron of dimensions
60 cm× 60 cm×6 mm is buried
into the ground with its face
vertical at a depth of not less
than 3 meters from ground
level.
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17. PLATE
EARTHI
NG
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19. Pipe Earthing
⚫ This is the most common and
best system of earthing as
compared to other systems
suitable for the same earth and
moisture conditions.
⚫ In this method the galvanized
steel and perforated pipe of
approved length and diameter in
place upright in a permanently
wet soil, as shown below.
⚫ The size of the pipe depends
upon the current to be
carried and type of soil. 19

20. PIPE
EARTHING
2
0

21. ⚫ The pipe is placed at 3.75 meters. The bottom of the pipe is
surrounded by small pieces of coke or charcoal at a distance of
about 15 cm. Alternate layers of coke and salt are used to
increase the effective area of the earth and to decrease the earth
resistance respectively.
⚫ Another pipe of 19 mm diameter and minimum length 1.25 meters
is connected at the top of GI pipe through reducing socket.
⚫ During summer the moisture in the soil decreases, which causes
an increase in earth resistance. So a cement concrete work is
done to keep the water arrangement accessible, and in summer
to have an effective earth, 3 or 4 buckets of water are put through
the funnel connected to 19 mm diameter pipe, which is further
connected to GI pipe.
⚫ The earth wire either GI or a strip of GI wire of sufficient cross
section to carry faulty current safely is carried in a GI pipe of
diameter 12 mm at a depth of about 60cm from the ground.
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