Electrical ACcessories MCQ Quiz - Objective Question with Answer for Electrical ACcessories - Download Free PDF

Explanation:

Service Connections Cable Conductor Material in Electrical Installations

Context: In electrical installations, particularly in Low Tension (LT) distribution systems, the choice of conductor material for service connections is crucial. The conductor material impacts the performance, durability, and safety of the electrical system.

Correct Option Analysis:

The correct option is:

Option 1: Aluminium

This option is correct because aluminium is a common material used for service connection cables in LT distribution lines. There are several reasons why aluminium is preferred in these applications:

1. Conductivity: Aluminium has good electrical conductivity, which makes it suitable for carrying current efficiently in electrical distribution systems. Although copper has higher conductivity, aluminium’s conductivity is adequate for LT distribution applications.

2. Cost-Effectiveness: Aluminium is more cost-effective compared to copper. The lower cost of aluminium makes it an economical choice for large-scale electrical installations, as the material costs significantly impact the overall budget.

3. Weight: Aluminium is lighter than copper, which reduces the weight load on poles and other supporting structures in the distribution system. This lighter weight makes installation easier and reduces mechanical stress on the infrastructure.

4. Corrosion Resistance: Aluminium naturally forms a protective oxide layer that resists corrosion. This characteristic enhances the durability and longevity of aluminium conductors, making them suitable for outdoor and exposed environments.

5. Compatibility with ACSR: Aluminium Conductor Steel Reinforced (ACSR) cables are commonly used in distribution lines due to their strength and conductivity. Using aluminium for service connections ensures compatibility with the ACSR lines, reducing potential issues related to different materials' thermal expansion or electrochemical reactions.

Additional Information

To further understand the analysis, let’s evaluate the other options:

Option 2: Galvanised Iron

Galvanised iron is not commonly used for service connection cables due to its poor electrical conductivity compared to aluminium and copper. Galvanised iron might be used for structural components or protective enclosures but not for conductors carrying electrical current.

Option 3: Copper

Copper is an excellent conductor of electricity and is often used in electrical installations. However, due to its higher cost compared to aluminium, copper is less frequently used for large-scale distribution lines where cost considerations are significant. Copper is more common in smaller-scale or high-value applications where its superior conductivity and reliability justify the expense.

Option 4: Silver

Silver has the highest electrical conductivity of all metals, but it is prohibitively expensive for use in standard electrical distribution systems. Silver is typically reserved for specialized applications where its exceptional conductivity is necessary, such as in high-frequency or high-reliability circuits.

Conclusion:

In electrical installations, using aluminium for service connection cables in LT distribution lines is a practical and economical choice. Aluminium offers a good balance of conductivity, cost-effectiveness, weight, and corrosion resistance, making it well-suited for this application. While other materials like copper and silver have their advantages, their higher costs limit their use in large-scale distribution systems. Understanding the properties and benefits of different conductor materials is essential for designing efficient and reliable electrical installations.

• Nichrome: This is a common choice for electric heating elements due to its several desirable properties:
  • High resistivity: Offers significant resistance to current flow, resulting in efficient heat generation.
  • High melting point: Can withstand the high temperatures involved in heating applications without melting.
• Good oxidation resistance: Resists corrosion at elevated temperatures, ensuring long element life.
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• Copper: While a good conductor of electricity, copper doesn't have a high enough resistance to efficiently convert electrical energy into heat.
  It would lose most of the energy as heat itself.
• Tungsten: While having a very high melting point, tungsten is also very expensive and oxidizes readily at high temperatures.
  This limits its practicality for most heating element applications.
• Aluminum: Similar to copper, aluminum is a good conductor and wouldn't be suitable for efficient heat generation due to its low resistance.

Concept:

Two-way switch is used for staircase wiring. In this lighting circuit, two switches control one lamp from two different positions. These two switches can be operated from separate positions such as above or below the staircase, from inside or outside of a room, or as a two-way bed switch, etc.

One-way switch can operate at only one location. It has two terminals i.e. ON and OFF.

The bad switch is the switch which is defective. We have to replace it when we find the switch goes bad.

A push switch is a switch which having a push button. If the button is pressed, the circuit will break. If is not pressed, the electricity will flow. The push switch is also known as a normally closed switch.

Different protection devices

1.) Moulded Case Circuit Breaker (MCCB)

• It is an electrical protection device that is used when the load current exceeds the limit. 
• MCCB is mainly used for both low and high-breaking capacity
• Their interrupting current ranges from around 10KA -85KA.
• Its trip current may be fixed as well as adjustable for overload and magnetic settings.

2.) Miniature Circuit Breaker (MCB)

• The MCB is an electromechanical device that guards the electric wires &electrical load against overcurrent so as to avoid any kind of fire or electrical hazards.
• MCB is mainly used for low-breaking capacity requirements mainly domestic.
• Its interrupting current rating is under 10KA.

3.) Residual Current Circuit Breaker (RCCB)

• This residual current device is basically an electrical wiring device that disconnects the circuit whenever there is leakage of current flow through the Human body or the current is not balanced between the phase conductor.
• It is the safest device to detect and trip against electrical leakage currents, thus ensuring protection against electric shock caused by direct contact.
• RCCB is generally used in series with an MCB which protects them from over current and short circuit current.
• Both phase and neutral wires are connected through an RCCB device. 

4.) Earth Leakage Circuit Breaker (ELCB)

• ELCB stands for Earth Leakage Circuit Breaker.
• They have the same function as RCCB but are voltage sensor device. 

The correct answer is Parallel.

Key Points

• If lamps are connected in parallel, we can have different switches for different lamps. 
• Also, if one lamp fails, the current will still flow in another lamp. 
• This is not possible in series, as all lamps will be connected by single path in that case. 

So, the correct option is 2: Fans and lamps in the domestic installation are connected in parallel.

Additional Information

Series and Parallel Connection:

Pig Tail:

This joint is also called as Pig-tail/Rat-tail/Twisted joint.

This joint is suitable for pieces where there is no mechanical stress on the conductors, as found in the junction box or conduit accessories box

Married joint:

A married joint is used in places where appreciable electrical conductivity is required, along with compactness.

As the mechanical strength is less, this joint could be used at places where the tensile stress is not too great.

Britannia joint:

This joint is used in overhead lines where considerable tensile strength is required. It is also used both for inside and outside wiring where single conductors of diameter 4 mm or more are used.

Both brazing and soldering are the metal joining processes in which parent metal does not melt but only filler metal melts filling the joint with capillary action.

Joint Design

a) Lap joint is the recommended form for these assemblies. Generally, the area of overlap in the joint is kept large in order to make it stronger than the weakest member of the assembly.

It is the recommended configuration for soldering. 

A common thumb rule: Allow an overlap of at least three times the thickness of the thinnest member.

b) Butt joints are avoided as they are weak due to small joint areas. They are not recommended unless strength requirements are very low and there is no need for a pressure seal at the joint.

c) Scarf Joint: To provide a greater joint area, scarf joints are recommended.

Explanation:

The given symbol represents buzzer. A buzzer or beeper is an audio signalling device, which may be mechanical, electromechanical (or) piezoelectric.

Important Points

• Bimetallic Lugs are mostly useful where an aluminum cable has to be terminated by a copper bus bar or copper contact.
• If Cable Lugs of only copper or aluminum are used, a galvanic action occurs due to dissimilar contact. The use of bimetallic lugs thus ensures a technically sound and durable joint.
• The Aluminium barrel is friction welded to the copper palm thereby achieving the best possible transition between barrel & palm.
• Copper lugs (cable lugs) are devices used for connecting cables to electrical appliances, other cables, surfaces, or mechanisms.
• The clamps that connect wires to an automotive battery are a common example of copper lugs, as are the ends of battery jumper cables

The married joint is an electrical joint used for jointing multi strand cables. If the wires are un-stranded, then interlaced with the wires of the other cable and married (twisted) together before finally being soldered.

This type of joint is used in places where appreciable electrical conductivity is required along with compactness. The mechanical strength for this joint is less. This joint is used at places where tensile stress is not so more

Tee joint is an electrical connection used for joining a branch conductor to a main conductor where the main conductor continues beyond the branch.

This type of joint is used in overhead distribution lines where the electrical energy is to be tapped for service connection.

A Britannia straight joint is used to connect two wires where there is a need to maintain high tensile strength. Example: Overhead lines

Britannia tee joint is used for overhead lines for tapping the electrical energy permanently to the service lines.

The western union joint is used when the connection must be strong enough to support long lengths of heavy wire. This splice was used to repair telegraph wires.

• A switch shall be installed at any height of 1.3 m above the floor level. As from the given option ideal height of a single-pole switch is 1.5 m.
• Socket-outlets shall be installed either 0.25 or 1.3 m above the floor as desired.
• The clearance between the bottom point of the ceiling fan and the floor shall be not less than 2.4 m.

The correct answer is option 3): Timer 

Concept:

A Timer Relay is a combination of an electromechanical output relay and a control circuit. The contacts will open or close before or after a pre-selected, timed interval.

 Additional Information

• Rectifier converts Alternating Current to Direct current
• A control transformer is a transformer that is used to step down the voltage to power the control devices of a circuit or machine.
• A limit switch is a switch operated by the motion of a machine part or the presence of an object. A limit switch can be used for controlling machinery as part of a control system

• A Single Pole Double Throw (SPDT) switch is a switch that has only a single input and can connect to and switch between 2 outputs.
• This means it has one input terminal and two output terminals.

IMPORTANT:

• In a half lap joint or halving joint, the material is removed from both of the members so that the resulting joint is the thickness of the thickest member.
•  Most commonly in half-lap joints, the members are of the same thickness and half the thickness of each is removed.
• Dovetail half-lap joint is a joint in which the housing has been cut at an angle which resists withdrawal of the stem from the cross-piece.
• The half-lap dovetail is a remarkably strongest and versatile joint.
• Its most common application is joining top rails to the sides of a carcass or the legs of a table.
• Due to its wedge shape, the dovetail is extremely effective at locking parts together.
• Because of its great mechanical integrity, a well-fitted, unglued half-lap dovetail can be an ideal joint for knockdown furniture.
• In cross half-lap joint, the joint occurs in the middle of one or both members, rather than at the end. The two members are at right angles to each other and one member may terminate at the joint, or it may carry on beyond it.
•  When one of the members terminates at the shin, it is often referred to as a tee lap or middle lap. In a cross lap where both members continue beyond the joint, each member has two shoulders and one cheek.
• Cross half-lap joint used for internal cabinet frames, simple framing and bracing.
• The mitered half lap is the weakest version of the joint because of the reduced gluing surface.
• It is used for visible framing applications where a mitered corner is desired.

The correct answer is option 2):(electromagnets)

Concept:

Electromagnets

•  Materials with low retentiveness lose magnetic flux density once the external magnetizing force is removed hence are useful in creating electromagnets.
• An electromagnet is a temporary magnet that should ideally have the property to behave as a magnet when current passes through it and lose magnetism as soon as current is stopped.
• Soft iron is generally used for making electromagnets because it has high magnetic permeability, i.e. it can easily gain magnetic properties when current is passed around the core and quickly lose when current is stopped.
• The soft iron inside the coil makes the magnetic field stronger because it becomes a magnet itself when the current is flowing
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