Download 2014 Electrical Installation Model Paper - IESL e

Sample Question Paper for Design of Electrical Installation
Question 1
(a). Compare the advantages and disadvantages of the TT system over the TN system?
[2]
(b). Analyze quantitatively the earth loop impedance and the earth fault current of TT
and TN-C-S systems
[2]
(c). Answer the questions using the figure and taking any suitable assumptions
(i).
What is the earthing arrangement?
(ii).
Calculate the maximum fault current of this system
(iii).
Calculate the fault voltage Uf? Is it dangerous?
[6]
(d). Explain the differences between a barrier and an enclosure in an electrical
installation
[2]
(e). What is ventricular fibrillation?
[1]
(f). It will be seen that 50 mA is considered to be the minimum lethal level of shock
current, and so, if a person’s body resistance is as low as 1000 Ω. What is the
voltage required to cause this current to flow through the body?
[2]
Question 2
(a). A 5 A semi-enclosed (BS 3036) fuse and a 10 A type B circuit breaker are in series
in a certain circuit. With the aid of suitable diagrams explain which device will
operate first in the event of a short circuit fault?
[4 ]
(b). Why do you need discrimination between Overcurrent Protective Devices
[2 ]
(c). Determine the maximum value of earth loop impedance (Zs ) permissible for a
semi-enclosed fuse (BS 3036) rated at 100 A for a normal voltage 230 V, for fixed
equipment.
[4 ]
(d). If a circuit was wired in 90 ◦C thermosetting cable with copper conductors, and had
a calculated fault current of 645 A with a disconnection time of 1.5 seconds,
calculate using the adiabatic equation the smallest permissible size circuit protective
conductor
[5]
Question 3
(a). An insurance office is supplied at 400/230 V 50 Hz and has the following
connected load:

4×30 A socket outlet circuits for computer use

1×30 A socket outlet circuit for general use

1.5 kW of fluorescent lighting

1.0 kW of tungsten lighting

1×6 kWcooker

2×600W microwave cookers

2×3 kW instantaneous type hand washers

2×2 kW hand dryers.
Determine the assumed maximum demand.
[8]
(b). The design current of a single-phase circuit is 35 A. The single-core p.v.c.
insulated cables run alone in p.v.c. conduit for a distance of 50m through an area
having an ambient temperature of 35 ◦C (100mm of the conduit passes through
thermal insulation). The voltage drop in the circuit must not exceed 5 V. Protection
is by a BS 1361 fuse. Determine the:
(i) fuse rating
(ii) minimum cable current rating
(iii) minimum cable c.s.a.
(iv) voltage drop in the cables.
[6 ]
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(a). An industrial process heater of rating 16 kW is fed at 400 V, 50 Hz. 3-Ф four wire
is to be installed in a factory using a P.V.C insulated non-armored copper
conductors multi core cable. Length of run is 25 m clipped direct to a wall.
Assuming maximum ambient temperature is 35 0C and protection by 3036 fuses,
calculate the maximum voltage drop and select a cable size? ( Ca=0.94, Cc=0.725)
[6 ]
Question 4
Certain installation (2 storey building) has the following loads.
Floor
AC Load(kW)
Power
for
Lighting Load socket outlets
(kW)
(kW)
2
25
6
12
1
1.5
3
6
(a). What is the size of the recommending transformer for the supply?
(b). Sketch a single line diagram with suitable protection scheme for the main
distribution board to satisfy above conditions.
[5 ]
(c). If all the cables are to be installed in cable tray and the operating temperature is
35 0C, find the required current carrying capacity of the cable for each load.
[5 ]
(d). Select the minimum cross section area of the cable for each load and calculate the
percentage voltage drop of the cables at load end.
[5 ]
(e). Select suitable circuit breaker rating for each outgoing circuits and main incoming
side (Standard Circuit Breaker Ratings:6A, 10A, 16A, 20A, 25A, 32A, 40A, 60A,
80A, 100A, 125A, 160A, 200A, 250A, 300A, 450A)
[5 ]
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