Bus Bar Chamber: This is used for distribution of supply to different branches for industrial and large domestic and commercial installations. The busbar chamber is an encloser of sheet metal inside which busbars, copper or aluminium, are mounted on insulators. For 3-Phase, 4-wire ac. supply 4 bars (T.P. &N.) and for 3-wire d.c. supply 3 bars (D. P. & N) are used. The rating of the busbar chamber depends on the load, the standard sizes are 32A, 63A, 100A etc. The width of the busbar chamber depends on the number of outgoing circuits.
3.What is stranded conductor? Why stranded conductor is more popular now a day’s? Mentioned the formula of number of strands and diameter of strands of stranding conductor?
Ans:
Stranding conductor conductor is now very popularly used in transmission, distribution of electrical energy. Generally aluminum is used for it.
But in building electrification , annealed coppler is also used as stranding conductor.
Annealing and stranding make the cable more flexible.
The number of strands are- 3,7,19,37 etc.
Function:
Stranded conductors have a number of advantages over solid (unstranded) conductors.
The stranded conductor is more flexible, voltage drop in conductor is reduced (due to elimination of skin effect) and also the chance of breaking of conductor is reduced.
4. What is cable ? Classify the cable. Describe it.
Ans:: A cable is a conductor, single or stranded, covered with suitable insulation. The insulation prevents leakage of current and thus minimises the risk of shock.
Classification:
Types of Cables for Electrical Wiring: The following types of cables are generally used for electrical wiring purposes.
(i) V.I.R. cable,
(ii) P.V.C. cable,
(iii) T.R.S. or C.T.S. cable,
(iv) M.S. cable,
(V)Weather-proof cable &
(vi) Flexible cable.
V.I.R. Cable: It consists of tinned-copper or aluminium conductors with a layer of vulcanized India-rubber insulation. The rubber is applied in three layers. A lapping of cotton tape is placed directly over the rubber and is vulcanized to it. A further protection is given by cotton braiding over the tapped and vulcanized rubber. The cotton is impregnated with wax compound. These cables are rarely used now-a-days.
P.V.C. Cable: It consists of copper (not tinned) or aluminium conductors covered with a layer of P.V.C. insulation. Single-core P.V.C. cable has no other protection. For two or three-core cables, the cores are laid side by side and is covered with a protective covering of P.V.C. This is called PVC cable.
** Single core cables are manufactured in 250-volt and 650-volt grades while two-core and three-core cables are manufactured in 250-volt grade only.
These cables are now-a-days extensively used both for domestic and industrial wiring.
** These are particularly suitable in the circumstances where acids, alkalies or other fumes are present.
** P.V.C. is affected by high temperature, when it may melt. These cables. Therefore, must not be used for connections to heating appliances, pendant lighting etc.
T.R.S. Cable: This cable consists of one, two or three VIR insulated conductors (tinned copper or aluminium) laid up flat with a closed cover of Vulcanized Tough Rubber Sheath. This cable is also known as Cab Tyre Sheathed (C.T.S.) cable.
** This cable does not deteriorate even after long exposure to moisture. So it can be used in wet conditions. These cables are very rarely used now.
. M.S. Cable: In this cable vulcanized rubber insulated cables are covered with a protective cover of closely fitted sheath of lead alloy.
These are available in single-core as also in two-core or three-core laid flat, and also with earth continuity conductor.
** These cables are completely waterproof. Therefore these are suitable for very damp conditions.
*** These can not, however, be used in places having acid and alkali fumes.
The cost is very high; not used now.
Flexible Cords: These are made of very fine gauge wires of large numbers so as to make it specially flexible.
These are used as connecting wires between the ceiling rose and lamp-holders, fans etc, or connecting portable appliances such as lamps, irons etc.
Twin twisted flexible cables are of common use and consist of several strands of copper conductors insulated with P.V.C
T’wo such cores are twisted together.
The sections of the cord ranges from 0.5 mm² (16/0.200 mm.) to 4.0 mm² (128/0.200 mm).
For connecting portable appliances which are to be earthed, three-core twisted flexible cords are used.
Flexible conductors with large cross-sections are termed as flexible cables
Weather-proof Cable: The weather-proof cable is used for outdoor purposes.
Such types of cables consist of three braids of fibrous yarn provided over the copper conductors.
The coper conductor are not generally tinned.
The braids are thoroughly saturated with a water-proof compound.
** The insulation is cheap, very durable, and does not deteriorate unless exposed to such high temperatures as will melt the compound.
These are used for external wiring where moisture is present and where fire-proof quality is not necessary.
FRLS Cable: PVC compounds are the most widely used sheathing material for low and medium voltage cables for electrical wiring installations.
PVC has inherent resistance to flame propagation,
but it emits large amount of thick, dense black smoke which blocks exit routes and creates suffocation making it difficult to extinguish the fire.
Burning PVC also emits halogen gas and HCL acid gas which is corrosive and can damage the equipments and instruments.
The properties of the sheathing material have, therefore, been modified so as to make it able to
(i) restrict flame propagation.
(ii) to reduce smoke emission which increases visibility,
(iii) emission of corrosive HCL acid gas. Cable with the sheathing of this modified material is called Flame Retardant Low Smoke (FRLS) cable.
This cable should be used for house and industrial wiring particularly in public buildings, school buildings, cinema halls, office buildings, hotels, hospitals, high-rise buildings, chemical plants etc., where fire may cause a havoc.
The cost of the cable is, however, much higher than PVC cables.
Note on anser::
A.Which material is used within cotton for VIR cable?
Ans: the cotton is impregnated with wax compound.
B Where and why PVC cable is suitably used?
Ans: These are particularly suitable in the circumstances where acids, alkalies or other fumes are present.
C. Where and why PVC cable is not suitable?
Ans: P.V.C. is affected by high temperature, when it may melt. These cables. Therefore, must not be used for connections to heating appliances, pendant lighting etc.
D. Where and why TRS or CTS cable is suitable?
Ans::This cable does not deteriorate even after long exposure to moisture. So it can be used in wet conditions. These cables are very rarely used now.
E. Where and why MS cable is suitable?
Ans::MS cables are completely waterproof. Therefore these are suitable for very damp conditions.
F. Where and why MS cable is not suitable?
ANS: These can not, however, be used in places having acid and alkali fumes. Because metal sheath reacts with acid and alkali and detoriates.
G. What are the disadvantages of PVC cables over FRLS cable ?
Ans::
H. What are the properties of FRLS – Flame Retardant Low Smoke cable?
Ans::
Able to
(i) restrict flame propagation.
(ii) To reduce smoke emission which increases visibility,
(iii) Emission of corrosive HCL acid gas. Cable with the sheathing of this modified material is called Flame Retardant Low Smoke (FRLS) cable.
I. What is the voltage grade of single core PVC cable?
Ans: 250 volt and 650 volt
J. What is the voltage grade of two core and three PVC cable?
Ans: 250 volt.
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