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WorksheetsISC Chap 8 2020 - CET 1423
Total questions: 35
Worksheet time: 9hrs 45mins
The three basic parts
of a cable are conductor, insulation and
armouring.
double insulation.
steel-wire insulation.
mechanical protection.
An advantage of using
copper as a cable conductor is that it is
fairly flexible.
lighter than aluminium.
higher electrical resistance.
often used for overhead lines.
If copper is used as in cables and busbars, then brass is commonly used in
heating elements.
terminals and plug pins.
plating of switch contacts.
electrical machines brushes.
An advantage of aluminium being used as conductors in electric cables instead of copper is that it is
fairly flexible.
lighter than copper.
a better conductor for small cables.
ductile and hence easier to work with.
SS 638 states that the conductor of an electrical cable shall be of copper if its cross-sectional area is
4 mm2 or less.
6 mm2 or less.
10 mm2 or less.
16 mm2 or less.
hich type of cables is prohibited to be used by SS638 in domestic installations?
Gold.
Silver.
Copper.
Aluminium.
One
of the requirements for electric cables is that the cross-sectional area of
the aluminium conductors shall not
be less than
4 mm2.
6 mm2.
10 mm2.
16 mm2.
Cables are often stranded to provide better
flexibility.
termination.
resistance corrosion.
current carrying capacity.
In the construction of electric cables, hard-drawn conductors are used in busbars and
overhead lines.
residential homes.
underground cables.
commercial and industrial buildings.
Which one of the following cables is most commonly used for the domestic installation?
Mineral insulated cable.
Rubber insulated cable.
Polyvinyl chloride cable.
Steel armoured PVC insulated cable.
In considering the current carrying capacity, the maximum conductor operating temperature for a PVC insulated cable is
300 C.
700 C.
900 C.
1100 C.
In a corrosive area, it is recommended to use
paper-insulated cable.
rubber-insulated cable.
silicone rubber-insulated cable.
polyvinyl chloride-insulated cable.
A reason of using silicone rubber cables instead of PVC insulated cables is that
they are very flexible.
they allow a reduction in conductor size.
they are able to retain the insulation properties after being burned for sometimes.
they have the added mechanical strength to withstand handling during installation.
What is the main function of sheathing or armouring in the construction of an electric cable?
To protect the conductor against corrosion.
To protect the cable from mechanical damage.
To prevent the ingress of moisture in the cable.
To protect the conductor against electrolytic action.
All cables for fixed wiring must be
protected by an enclosure or be provided with a layer of insulating material. This is known as
shock protection.
overload protection.
electrical protection.
mechanical protection.
Which one of the following parts provides the highest degree of mechanical protection to an insulated cable buried directly under the ground?
PVC sheath.
Lead sheath.
Steel Armour.
PVC bedding.
Fig 10.1 shows an armoured cable. The part named (d) is the
pvc tape.
pvc sheath.
pvc bedding.
pvc insulation.
Cross-linked polyethylene (XLPE) cables are
increasing in use nowadays as compared to PVC armoured cables because it can
be operated at a higher temperature. This means that there is a reduction in
cost.
current flow.
conductor size.
insulation thickness.
The type of cable insulation suitable for the 22 kV underground distribution system is
rubber.
silicone rubber.
polyvinyl chloride.
cross-linked polyethylene (XLPE).
What is the maximum operating
temperature for the XLPE cables?
300 C.
700 C.
900 C.
1100 C.
hich one of the following cables is commonly used for fire alarm circuit?
Rubber insulated cable.
Silicone rubber insulated cable.
Cross-Linked Polyethylene cable.
Polyvinyl chloride insulated cable.
The new colour code changes in Singapore is means for
protective conductors only.
single-phase flexible cords.
d.c. fixed low voltage cables.
three-phase fixed low voltage cables.
Fig 10.2 shows a 3-phase distribution board installed with the new cable colours. What shall be the colours for the 3-phase final circuit?
Red, Red and Red.
Red, Yellow and Blue.
Brown, Black and Grey.
Brown, Brown and Brown.
What is the colour for neutral conductor in the new colour code for fixed low voltage cables?
Blue
Grey
Black
Brown
What is the basic identification number used to distinguish the neutral conductor from the phase conductors of a paper-insulated cable?
0.
1.
2.
3.
The colour combination of green and yellow is reserved exclusively for identification of the
phase conductor.
neutral conductor.
protective conductor.
earthed neutral conductor.
Tape.
Sheath.
Bedding.
Armouring.
A cable which consists of one or more cores, each containing a group of fine wires is meant to provide
greater flexibility.
higher current rating.
higher voltage rating.
better mechanical strength.
To be justified as a flexible cord, the cross-sectional area of each core of a flexible cable must not exceed
1.5mm2
2.5mm2
4.0mm2
6.0mm2
The colour code used to identify the phase, neutral and circuit protective conductor in a 3-core flexible cord are
red, blue and green/yellow respectively
red, black and green/yellow respectively
brown, blue and green/yellow respectively
brown, black and green/yellow respectively
A low voltage cable has the following voltage marking along its insulation: 600 V / 1000 V. This means that
600 V voltage to earth and 1000 V voltage between lines.
600 V voltage to earth and 1000 V voltage between line and earth.
600 V voltage to earth and 1000 V voltage between line and neutral.
600 V voltage to neutral and 1000 V voltage between line and earth.
The drop in voltage from the origin of the circuit to any point in the circuit should not exceed
1% of the nominal voltage.
2.5% of the nominal voltage.
4.0% of the nominal voltage.
6.0% of the nominal voltage.
What is the maximum permissible voltage drop in a single-phase, 230V electrical installation?
5.75V
9.20V
10.00V
16.00V
What kind of protection shall be provided to the cables passing through holes in metal work?
Against moisture.
Against abrasion.
Against corrosion.
Against damage by heat.
What would be the major safety problem in using the new colour code for fixed low voltage cables?
Supply voltages are different.
Difficult to follow the colours used in the flexible cords.
The change of the colour blue from phase L3 to neutral.
Many countries are not implementing the new colour code.
