Power and control cables. Questions & Answers

Power and control cables.

1. Define conductor.

Conductor: A material of low resistance used to transmit electrical energy. Examle
wires, cables, bus bars etc.

2. Define unprotected insulated wire.

Unprotected insulated wire: Unprotected insulated wire is which the insulation of the
wire is not covered by a protective sheathing to prevent it from mechanical damage.

3. Define cable.

Cable: One or more insulated conductor enclosed in a protective mechanical
sheathing of either GI wire or GI strip or aluminium to protect the insulation from
mechanical damage.

4. Define insulated wire.

Insulated wire: A conductor or multi-stranded conductor which has a insulating
material on it is called a insulated wire.

5. Explain briefly about armouring for an under grounded cable.

Armouring is required to protect the cores from mechanical damage.

6. Explain briefly about grounding of cable trays.

Cable trays are grounded because to avoid any shocks to personnel incase of leakage.
A grounding wire runs at the side of tray through a parallel groove clamp through out
the length of the cable tray. If trays are one above another we can loop up the
grounding wire to the tray below. This saves extra ground wire.

7. What are the differences between the power and control cable?

Power cable: It is used for supplying current to load. It is of larger current carrying
capacity available in single core, 2 cores, 3 cores, 3 cores, and 4 cores. Single core
is available upto 1000 mm2. Usually power cables are of aluminium. These cables
are graded for higher voltages and possess more cross section area.
Control cable: Control cables are used for control purposes for logics, indication or
annunciation etc. These are of lower current carrying capacity and voltage grading is
also less. These are of less cross sectional area are available in pairs of 2,5,10,25,50
etc.

8. What is the purpose of using corrosion inhibiting compound?

It is used for aluminium conductors while crimping to a lug or ferrule. It prevents
corrosion of aluminium conductor due to oxidation and due to saline atmosphere.

9. Why aluminium armouring for single core 1000 mm2 is used?


Aluminium armouring for single core 1000 mm2 is used so that heating will not take
place due to the flux around the conductor, as the aluminium is a non-magnetic
material.


10. What is resistance of copper compare to the aluminium?

Copper is less resistive than aluminium.

11. What is applied over the steel tape armour of PILC cable as serving?

Bituminous covered jute.


12. What is used as insulation for PILC cable?

Impregnated paper.

13. A small quantity of impurity reduces how much of conductivity of copper?

35% of conductivity will be reduced due a small impurity in the conductor.

14. Why cast aluminium tri-foil clamp is used in single core cables laying?

When three conductors are clamped together the fluxes around the conductors are get
cancelled

15. What are the parts of a cable gland?

a. Check nut.
b. Nipple.
c. Metal washer.
d. Neoprene rubber.
e. Metal washer.
f. Compression nut.

16. What are the advantages of PVC insulated cable?

a. Plumbing is not required. Joints can be made easily.
b. As PVC is light the injury caused to it while laying is less.
c. It is corrosion resistant.
d. It has high fire retarding property.
e. It does not break down even if moisture enters.

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