Electrical Installation Estimating & Costing - gtbit

restmushroomsElectronics - Devices

Oct 7, 2013 (4 years and 1 month ago)

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Short answer type question

Q1. What is the maximum number of point of light, fan and socket
-

outlets that can be connected in one
sub
-
circuit?

Ans. Ten.


Q2. What is the maximum load (light and fan) that can be connected in one sub
-
circuit?

Ans. 800 Watts
.


Q3. On what basis is the number of circuits/ sub
-
circuits determined in house wiring installations?

Ans. The number of circuits and sub
-
circuits is decided on the basis of total number of point to be wired
and the total load to be connected to the suppl
y system.


Q4. Which system is used for distribution of electrical energy in a building?

Ans. Distribution board system.


Q5. Which system is used in connections of various lamps or appliances in parallel?

Ans. Loop
-
in

system.


Q6. Which of the following
wiring system is commonly used for light/fan load in domestic and commercial
buildings?

(a) Cleat wiring


(b) Casing
-
capping wiring


(c) TRS wiring


(d) Lead sheathed wiring


(e) PVC wiring


Ans.

(e) PVC wiring


Q7. Which wiring system is employed in me
chanical workshops?

Ans. Conduit wiring system (surface or concealed).


Q8. What are that points which will be consider in selecting the wiring for a particular installation?

Ans. The main points, which are considered in selection of the type of wiring for

a particular installation,
are safety, durability, appearance mechanical protection, permanency, accessibility and cost (initial as well
as maintenance).


Q9. What is different between wire and cable?

Ans. Single wire, may be bare or covered with insulati
on is called the wire while several wires stranded
together is called the cable.



Q10. Why conductor is covered with insulating material?

Ans. The conductor is covered with insulating material so as to prevent leakage of current from the
conductor.


Q11.
What are the essential properties, which the insulation used in cable must posses?

Ans. The insulating materials used in cables must have the properties of light resistivity, high flexibility,
high dielectric strength, non
-
inflammability, non
-
hygroscopicit
y, highly resistive to moisture, acids or
alkalies and capability to withstand high rupturing voltage and high temperature without much
deterioration.


Q12. Which insulation is most widely used for covering wires/cables used in internal wiring?

Ans. PVC.


Q13. Why multi
-
stand conductors are preferred over solid conductors?

Ans. Multi
-
strand conductors are preferred over solid conductors because they provide flexibility and
durability.


Q14. PVC cables are most widely used in internal wiring. Why?

Ans. PVC c
ables are most widely used in internal wiring because PVC insulation provides better flexibility,
has better insulation qualities, has no chemical effect on metal of wire and gives smaller diameter of cable.


Q15. Where are flexible cords used?

Ans. Flexib
le cords are used as connecting wires for such purposes as from ceiling rose to lamp holder,
socket outlet to portable apparatus such as radios, fans, lamps etc.


Q16. What is meant by voltage grading of cables?

Ans. Voltage grading of cable specifies the
safe voltages which the insulation of the cable can withstand.


Q17. How the size of a wire or cable is given?

Ans. The size of a wire or cable is specified giving the number of strands used and diameter of each strand
or giving the area of cross
-
section o
f conductor used.


Q18. How are cable specified?

Ans. The cables are specified providing size of conductor used, type of conductor used, number of cores
that cable consists of, voltages grade and type of cable.


Q19. What is meant by distribution board?

An
s. Distribution board is an assembly of parts, including one or more fuses or circuit breakers, arranged
for the distribution of electrical energy to different circuits or other distribution boards known as submain
distribution boards.




Q20. What is mean
t by a switch?

Ans. A switch is a device that is used for making or breaking the electric circuit in a convenient way.


Q21. What for ceiling rose is used?

Ans. Ceiling rose is used for connecting the pendant lamps, fans or fluorescent tubes to the install
ation
through flexible plastic or silk covered wire.


Q22. What is meant by a fuse?

Ans. Fuse is a devices used in an electrical circuit for protecting electrical equipment against overloads
and/or shor
-
circuits.


Q23. On what principle does the fuse opera
te?

Ans. The action of a fuse is based upon the heating effect of the electric current. During overloads or short
circuits the fuse gets heated upto melting point due to excessive current and breaks the circuit.


Q24. What kind of protection is offered by
a fuse?

Ans. The fuse provides protection against short
-
circuits and overloads.


Q25. What function does the fuse perform?

Ans. The function of a fuse wire is (i) to carry the normal working current safely without heating and (ii) to
break the circuit when

current exceeds the limiting current.


Q26. Give the names of five materials with their melting points which are used for fuse element.

Ans. The materials commonly used for fuse elements are silver, tin, lead, copper and

aluminium. Their melting points a
re 980º C, 240º C, 328º C, 1,090º C, and 665º C, respectively.


Q27. What material is mostly used for an ordinary fuse wire?

Ans. Copper or lead
-
tin alloy.


Q28. What is fuse link?

Ans. Fuse link is that part of the fuse which needs replacement when the fu
se blows out.


Q29. On what factors does the current carrying capacity of a fuse depend?

Ans. The current carrying capacity of a fuse depends upon the permissible temperature rise of the contacts
of the fuse holder, size of fuse wire, fuse material and the

surrounding of the fuse.


Q30.On What factors does the fusing current depends?

Ans. The fusing current depends upon (i) diameter of wire (ii) length of wire (iii) fuse material (iv) x
-
section area (round or rectangular) (v) size location of terminals (vi)

types of enclosure used (vii) type of
surface etc.


Q31. What are the purposes of using quartz sand as filler materials in the construction of HRC fuse?

Ans. The purposes of using quartz sand as filler material in the construction of HRC fuse are to absor
b heat
at a very high rate, to produce a substance of high resistance and avoid the oxidation of silver element.


Q32. Can the HRC fuse be used for both ac and dc circuits. If so under what condition?

Ans. In general an HRC fuse meant for ac circuit may no
t be used for dc circuits; but however, a fuse
satisfying the requirement of arc voltage can be used on both ac and dc circuits.


Q33. What is meant by earth continuity conductor?

Ans. The conductor, by means of which the metal body of an equipment or an a
pplication is connected to
the earth, is known as earth continuity conductor (ECC).


Q34. What are maximum permissible values of resistance of earth system for (a) Large
power stations (b)
major power station (c) small substations (d) in all other cases?

A
ns. Maximum permissible value of resistance of earth system are as following:



Large power stations


-
0.5Ω


Major power station


-
1.0 Ω


Small power station


-
2.0 Ω


In all other cases


-
5 Ω maximum



Q35. What should be the minimum size of earth continuity conductor?

Ans.
The cross
-
section of earth continuity conductor should not
be either less than 2.9 mm² (14 SWG) or
half of the installation conductor size.


Q36. What is harm if earth resistance exceeds the permissible value of earth resistance?

Ans.
The sensitivity of the protective equipment, system voltage and the maximum faul
t current directly
relate to permissible value, then in the event of earth of earth resistance. In case the earth resistance exceeds
the permissible value, than in the event of earth fault, the fault current may not reach a sufficient value to
operate the
protective equipment (such as fuses or relays) and dangerous condition may arise.


Q37. What is an earth electrode?

Ans.
Any wire, pipe, rod or metal plate embedded in earth for the purpose of making an effective electrical
connection with the general mass

of earth is known as earth electrode.


Q38. What is an earthing lead?

Ans.
The wire which connects overhead earth wire or any other apparatus to be earthed to the earth
electrode is known as earthing lead.



Q39. Why charcoal and salt is used in earthing.

Ans.
Generally alternate layers of charcoal and salt are used to increase the effective area of the earth and
to reduce the earth resistance respectively.


Q40. What is the average resistance of a human body?

Ans.
About 1,000 Ω.