Wiring Accessories Interview Question - Day 1

[Q:-01] What are the names of electrical accessories used in house wiring ?

Ans :

(i) Wiles & Cables,

(ii) Switches,

(iii) Plugs & Sockets,

(iv) Lamp holders,

(v)ceiling roses,

(vi) Fuses,

(vii) Cut-out,

(viii) Adopters,

(ix) Battens or conduit pipes,

(x)Distribution boards, and

(xi) Switch Boards ,and

(xii) Junction boxes.

[Q:-02] What do you mean by controlling accessories ?

Ans :

      One-way switch, two-way switch, intermediate switch, iron clad main switches and isolators, which are used to control the flow of current, are called controlling accessories.

[Q:-03] What is cable ?

Ans :

Conductor covered with insulation is termed as cable.

[Q:-04] What is the difference between wire and cable ?

Ans :

A bare conductor is termed as wire whereas insulated conductor is termed as cable.

[Q:-05] How are the wires or cables classified ?

Ans :

The wires or cables are classified according to

(i) the conductor,

(ii) voltage grading,

(iii) number of cores &

(iv) type of insulation.

[Q:-06] How Is the specification of a cable given ? Give an example.

Ans :

      The specification of a cable is given by the voltage grade, the size of the cable, type of conductor (copper or aluminium), number of cores (single or twin etc.), type of insulation and protection (V.I.R, P.V.C. etc.)

      Example-250 volt grade, 2.5 sq. mm, 1/1.80 mm, Aluminium conductor, Twin core, P.V.C. insulated cable.

[Q:-07] Name the different types of cables.

Ans :

V.I.R, C.T.S or T.R.S, P.V.C. Weather proof, Lead sheath, Flexible cord, Mineral insulated cables etc.

[Q:-08] What are the sizes of conductors (both aluminium and copper) commonly used in house wiring ?

Ans :

      Aluminium conductor-1.5 mm² (1/1.40 mm), 2.5 mm² (1/1.80 mm), 4 mm² (1/2.24 mm or 7/0.85 mm), 6 mm² (1/2.80 mm or 7/1.06 mm), 10 mm² (1/3.55 mm or 7/1.40 mm) etc.

      Copper conductor :-0.96 mm² (1/1.12 mm), 1.29 mm² (3/0.736 mm), 1.93 mm² (3/0.915 mm), 2.90 mm² (7/0.736 mm), 4.52 mm² (7/0.915 mm), 6.45 mm² (7/1.12 mm) etc.

[Q:-09] What are the advantages of using stranded conductors than single solid conductor ?

Ans :

      Stranded conductors become more flexible. It can carry more current due to elimination of the skin effect to a great extent. The chance of breaking is reduced so much.

[Q:-10] What tools are generally used for measuring the size of a conductor ?

Ans :

      The micrometer and standard wire gauge are used for measuring the proper diameter and the gauge of the conductor respectively.

[Q:-11] What insulation is used in C.T.S. or T.R.S, P.V.C, V.I.R1 M.S. and M.I.C.C. cables ?

Ans :

      C.T.S. or T.R.S. cable—Vulcanized Tough Rubber Sheath.

P.V.C. cable—Poly Vinyl Chloride insulation.

V.I.R. cable— Vulcanized India Rubber insulation.

M.S. cable—Vulcanized Rubber insulation covered with lead sheath.

M.I.C.C. cable—Magnesium oxide insulation covered with copper sheath.

[Q:-12] What is the purpose of providing insulation on current carrying conductor ?

Ans :

      The insulation is provided to prevent leakage of current and electric shock.

[Q:-13] On what factors does the thickness of the insulation depend ?

Ans :

The magnitude of the voltage on the conductor.

[Q:-14] What do you understand by voltage grading of cable ?

Ans :

Voltage grading of cable means that the insulation of the cable can withstand the specified voltage safely.

[Q:-15] What difference will you find for high voltage and low voltage cables ?

Ans :

      The thickness of the insulation is comparatively greater in high voltage cable rather than low voltage cable of same size.

[Q:-16] What is insulation resistance ?

Ans :

      The resistance offered by an insulating material to the flow of leakage current through it, is known as insulation resistance.

[Q:-17] On what factors does the insulation resistance depend ?

Ans :

      Insulation resistance depends upon

(i) length of the cable,

(ii) thickness of the insulation and

(iii) volume resistivity of the insulating material.

[Q:-18] What is the relation between insulation resistance and length of a particular cable ?

Ans :

      For a particular cable, insulation resistance is inversely proportional to its length. When the length of the cable increases the insulation resistance decreases and vice-versa.

[Q:-19] What are the factors responsible for affecting the resistance of an insulation ?

Ans :

(i) Insulation resistance decreases with the rise in temperature.

(ii) It decreases with the increase in humidity.

(iii) In decreases with the increase in applied voltage.

[Q:-20] What are the common causes of Insulation failure of an electrical apparatus ?

Ans :

The causes are as follows :—

(i) Accumulation of oils and dirts.

(ii) Absorption of moisture.

(iii) Mechanical injury.

[Q:-21] What is the effect of moisture in the insulating materials ?

Ans :

      Insulation resistance is decreased due to increase in dielectric loss caused by the absorption of moisture.

[Q:-22] Why are C.T.S. cables not used in places exposed to direct sun light ?

Ans :

Because the insulation of C.T.S. cable does not withstand so much heat.

[Q:-23] Why is the current rating higher for mineral insulated cable than that of V.I.R. cable ?

Ans :

      The current carrying capacity of a cable is limited by the permissible temperature rise of its insulation. Since the permissible temperature rise of the mineral insulated cable is 72°F being higher as compared to 57°F for the V.I.R. cable, the current rating is higher for mineral insulated cable than that of V.I.R cable.

[Q:-24] What are the factors to be considered while determining the size of conductor ?

Ans :

The following three factors are to be considered :—

(i) Mechanical strength,

(ii) Current carrying capacity,

(iii) Voltage drop.

[Q:-25] Why are switches used in electrical circuit ?

Ans :

      The switches are used to make and break the electric circuits.