House Wiring and Its Components

Kathmandu ; Urja Khabar brings out an informative column, 'Urja Gyan', every Friday. This week, we provide information on household electrification, or house wiring, along with multiple-choice questions and answers. We dealt with magnets, their types, and properties last week.

(1) What is House Wiring ?
Answer: House wiring refers to the fitting of electrical wires in a house for providing electricity to lights and electrical appliances. The required materials for house wiring are given below:

Wires, Main Switch, Metal Clad Switch, MCB (Miniature Circuit Breaker), Socket, Plug, Switch, Switchboard.

Given below is the detail explanation of these materials:

1. Wires : Electrical wires are usually copper and are of different sizes such as 3/20, 3/22, 7/22, 7/20, etc. For high-power appliances like heaters, 7/20 or 7/22 wires are used. For lighting, 3/20 or 3/22 wires are used. The first figure (i.e., 3 or 7) refers to the number of strands of the wire, and the second figure (i.e., 20 or 22) refers to the thickness of each strand.

2. Main Switch : The main switch is single-phase and three-phase. Single-phase main switches are the ones that most homes use, and they are of two types:

• Metal (Iron) Main Switch
• MCB (Miniature Circuit Breaker)

3. Metal Clad Switch : Metal clad switches are available in different capacities such as 15A, 32A, and 60A. These switches consist of a kit-kat fuse, into which a thick or thin fuse is inserted according to need.

4. MCB (Miniature Circuit Breaker) : MCBs automatically switch off during a fault or overload. MCBs do not use fuse wire as in the case of traditional fuses. MCBs are now standard in home wiring and are available in ratings such as 3A, 6A, 16A, 20A, 32A, and 60A.

5. Socket : Sockets (or female connectors) are mounted on walls/surfaces and are 5A and 15A rated. Sockets are of two types:

• 2-pin socket
• 3-pin socket (where earthing is required)

6. Plug :Plugs (or male connectors or tops) are available in 5A and 15A ratings. 5A plugs are available in 2-pin and 3-pin varieties. 15A plugs are available in 3-pin varieties only.

7. Switch : A switch controls the flow of electricity to lights and appliances. Two switches are:

• 5A switches (used for lights)
• 15A switches (used for power points like heaters, rice cookers, etc.)

Today, 15A sockets include built-in switches.

8. Switchboard : Switchboards are constructed from wood or plastic and come in different sizes, i.e., 3.5" × 3.5", 4" × 7", and 8" × 12". Nowadays, plastic switchboards are more widely used.

Multiple-Choice Questions (MCQs)

1. What is the cross-sectional area of a rabbit conductor?
(A) 60 sq. mm
(B) 50 sq. mm
(C) 40 sq. mm
(D) 30 sq. mm
✔ Answer: (B) 50 sq. mm

2. What is the minimum insulation resistance in house wiring?
(A) 10Ω
(B) 5Ω
(C) 2Ω
(D) 15Ω
✔ Answer: (B) 5Ω

3. What should be checked in the preventive maintenance of a lead-acid battery?
(A) Battery voltage
(B) Electrolyte level
(C) Wires and terminals
(D) All of the above
✔ Answer: (D) All of the above

4. What was the kind of wiring used when electricity distribution began in houses?
(A) Cleat wiring
(B) Wood pattern wiring
(C) Surface conduit wiring
(D) Concealed conduit wiring
✔ Answer: (A) Cleat wiring

5. What does the power factor depend on?
(A) Load
(B) Frequency
(C) Supply voltage
(D) All of the above
✔ Answer: (A) Load

6. How many volt-amperes are there in one kilovolt-ampere (kVA)?
(A) 100 VA
(B) 1000 VA
(C) 1200 VA
(D) 1500 VA
✔ Answer: (B) 1000 VA

7. In house wiring, where should the switch be placed?
(A) Phase line
(B) Neutral line
(C) Either phase or neutral
(D) None of the above
✔ Answer: (A) Phase line