Electrical Wiring MCQ | Electrical Wiring Questions and Answers

Answer.2. 0.6 m

Rules for cleat wiring (as per BIS No 732 1963)

The following points should be kept in mind

(i) Cleat wiring should not be installed in moist places.

(ii) The height of wiring not be installed in moist places.

(iii) One wire should be 3 meters from the ground.

(iv) The distance between two-cleat should not be more than 60 cm (0.6m).

(v) All wires should be straight.

(vi) To open the wires from the ceiling or walls, PVC conduct pipe should be used.

(vii) For more than three wires, used more than one cleat.

Answer.1. 1 m

Every switchboard shall comply with the following provisions, namely: –

(i) A clear space of not less than 1 meter in width shall be provided in front of the switchboard.

(ii) If there are any attachments or bare connections at the back of the switchboard, the space (if any) behind the switchboard shall be either less than 20 centimeters or more than 75 centimeters in width, measured from the farthest outstanding part of any attachment or conductor.

(iii) If the space behind the switchboard exceeds 75 centimeters in width, there shall be a passage way from either end of the switchboard clear to a height of 1.8 meters.

Answer.2. Indian electricity rules, 1956

Explanation:-

According to the Indian electricity rule 1956

• The supplier shall ensure that all electric supply lines, wires, fittings, and apparatus belonging to him or under his control, which are on a consumer’s premises, are in a safe condition and in all respects fit for supplying energy the supplier shall take due precautions to avoid danger arising on-premises from such supply lines, wires, fittings, and apparatus.
• Service lines placed by the supplier on the premises of a consumer which are underground or which are accessible shall be so insulated and protected by the supplier as to be secured under all ordinary conditions mechanical, chemical, or other injuries to the insulate.
• The consumer shall, as far as circumstances permit, take precautions for the safe custody of the equipment on his premises belonging to the supplier.
• The consumer shall also ensure that the installation under his control is maintained in a safe condition.

Answer.1. Only i

A wide range of busbar systems is available and can be used for single or three-phase distribution to many types of applications ranging from lighting to heavy-duty machines in factories. This consists of copper or aluminum busbars mounted on insulators and enclosed in standard lengths of steel trunking, which are arranged to be fitted together thus forming a continuous busbar along the entire length of the distribution route. It is sometimes more economical to use busbars in place of long runs of sub-main cables.

In the case of an isolated phase bus system of continuous type, the enclosures are electrically continuous throughout the length.  Aluminum is used for wiring continuous bus bars because its cost is lesser than copper.

Answer.3. Both metal-sheathed wiring and TRS 

Explanation:-

(i) Cable Tyre Sheathed or Tough Rubber Sheathed or Batten

Wiring Material Used: The various materials used in batten wiring are CTS or TRS and PVC cable, and metal-sheathed wiring, straight teak wooden batten (at 10 mm thick), tinned brass link clip (buckle clip), and brass pins

TRS wire means that it has insulation covering of tough rubber sheath. TRS wires arc is sometimes also referred to as CTS (cab tyre sheathed) wires. PVC wire is one that has insulation covering polyvinyl chloride.

Answer.4. 2

The safety factor used for the current rating in a power installation is 2. For an AC motor with known output power, in addition to its efficiency, it is also necessary to know its power factor. Only then can its input current be known on the basis of its input power, hence its safety factor is 2.

Answer.1. Less than 1.25 m

Explanation

A flexible conduit is used for the final connection to motors so that the vibrations of the motor are not transmitted throughout the electrical installation and to allow for modifications to be made to the final motor position and drive belt adjustments.

The maximum length of flexible conduit in a motor installation is 1.25 m. The motor should be fitted with a flexible conveyor tube between the starter and the motor and its length should not exceed 1.25 meters. A conductor measuring less than 3/0.915 mm copper conductor cable or 1/1.80 mm aluminum conductor cable should not be used for power cord installation.

Answer.2. All equipment used in power wiring shall be of ironclad

The purpose of this switch is to control all the sub-circuits provided in the building. It is enclosed in an iron box and is called Iron Clad Switch.

All equipment used for power wiring in connection with motor installation shall be iron clad because of safety purposes and easily switch on and off the motor in case of emergency.

All metal parts of the electrical installation such as metal conduits, light fittings, iron-clad main switches, iron-clad distribution, cable sheaths, etc., should be earthed.

Answer.4. i, ii, & iii

Method of connecting Electrical equipment to supply

Electrical equipment can be connected by following two methods-

1. Tee or Joint Box method
2. Looping method

i) Tee or Joint Box method- In this method joints lamps, fans, etc. are connected in the joint box, cutout, three plate ceiling rose, connecter, etc. In this method first of all phase wire is connected and joined with the switch and then upto the lamp from the switch, whereas neutral is directly joined with the lamp, as shown in the figure. More wires need more joint boxes. This may also cause more faults. Therefore the method is used for Temporary wiring.

The advantage of this system is cables can be laid and connected during the first fix stage of the installation. This method is quicker and easier to connect accessories, as there are only one or two cables present the majority are within the joint box at an earlier stage of the installation.

The disadvantages will show up after the installation is finished. It can be difficult to trace faults or carry out cable tests when, for example, a chipboard floor has been laid. Another weakness is the practical ease of access to all the joint boxes. Ideally, marked traps cut and fitted directly over the joint box during the construction stage would provide a way out of this problem.

ii) Looping Method – In this method no joint box or ceiling rose is used. All the joints are completed on a switch or holder. One phase wire is brought to the second switch which makes a loop. This is shown in fig. Nowadays this method is mostly used. This neutral wire goes from one lamp to another.

Advantages of looping system

i) Number of joint boxes or ceiling roses is needed.

ii) Faults can early be heated.

iii) No tapping is required as there is no joint.

Disadvantages

i) More wire is needed in this system.

ii) More copper loss.

iii) More expenditure is needed.

Answer.1. 8

According to the Indian electricity rule, the number of points in light circuits should not exceed 10 or the total load on the circuit should not exceed 800 watts.

If 1 lamp is 100 watt

Total lamp can be installed in single circuit = 800/100 = 8