NABTEB GCE 2023 ELECTRICAL INSTALLATION ( O’ LEVEL) ANSWERS

PART I

(1ai)
Draw the diagram

(1aii)
Draw the diagram

(1aiii)
Draw the diagram

(1aiv)
Draw the diagram

(1av)
Draw the diagram

(1bi)
Capacitor:
– Stores and releases electrical energy.
– Filters signals in electronic circuits.
– Blocks direct current (DC) while allowing alternating current (AC) to pass.

(1bii)
Transformer:
– Transfers electrical energy between two or more coils through electromagnetic induction.
– Steps up or steps down voltage in AC circuits.
– Isolates different parts of an electrical system.

(1biii)
Inductor:
– Stores energy in a magnetic field when current flows through it.
– Opposes changes in current.
– Used in filters, transformers, and other electronic circuits.

(1biv)
Wall bracket:
– It is used for mounting or supporting electrical equipment such as switches, outlets, or fixtures.

(1bv) Resistor:
– Limits or controls the flow of electric current.
– Converts electrical energy into heat.
– Used to set the bias point in electronic circuits and control current flow.
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(2a)
(i) Cable Selection: The regulations outline the types and sizes of cables suitable for surface installations. It considers factors such as current rating, voltage drop, and environmental conditions.

(ii) Mechanical Protection: Surface wiring must be adequately protected against mechanical damage. This can include using conduit, trunking, or appropriate cable clips to ensure the cables are secure and shielded from impact or wear.

(iii) Fixing Methods: The regulations specify the acceptable methods for fixing surface cables, including appropriate distances between fixings and guidelines for routing the cable.

(iv) Cable Supports: Surface cables should be appropriately supported, taking into account factors such as cable size, weight, and the expected load. This ensures that cables are not suspended or stretched unsupported, reducing potential damage or strain.

(v) Clearances and Routes: Adequate clearance must be provided between surface-mounted cables and other services or building features to maintain safety and prevent any risk of mechanical damage or overheating.

(vi) Switches and Electrical Accessories: The regulations provide guidance on positioning switches, sockets, and other electrical accessories in surface installations, ensuring their accessibility and compliance with safety standards.

(vii) Earthing and Bonding: Surface installations require appropriate earthing and bonding to ensure electrical safety and minimize the risk of electric shocks or fire hazards.

(2b)
A switch is a device that is used to open or close an electrical circuit. The primary function of a switch is to control the flow of electric current in a circuit. When the switch is in the “on” position, it allows current to flow through the circuit, completing the electrical path and allowing devices (such as lights or appliances) to operate. When the switch is in the “off” position, it interrupts the flow of current, effectively disconnecting the circuit and stopping the operation of connected devices.
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PART II

(4a)
(i) Joint: A joint in electrical installation refers to the connection between two or more conductors. It is essential for creating a secure and reliable electrical connection.

(ii) Soldering: Soldering is a technique used to join two or more metal parts together using a filler metal called solder. The solder is melted and applied to the joint, creating a strong and permanent connection.

(iii) Brazing: Brazing is a similar technique to soldering, but it involves using a higher temperature and a different filler metal. Brazing is typically used for joining metal parts that require a stronger connection, such as pipes or heavy-duty electrical components.

(4b)
(i) Temperature: Joint connections can be made at room temperature, while brazing requires higher temperatures to melt the filler metal and create the connection.
(ii) Strength: Joint connections may not be as strong as brazed connections. Brazing provides a stronger bond due to the higher temperatures and the use of a stronger filler metal.
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(5a)
(i) Cable Cutters: Used for cutting the MICC cable to the desired length.

(ii) Stripping Tools: Used to strip the outer sheath and insulation from the cable ends.

(iii) Crimping Tools: Used to crimp connectors onto the exposed copper conductors for a secure connection.

(iv) Heat Shrink Tubing: Applied over connections and terminations, heat shrink tubing provides insulation and protection against environmental factors.

(v) Wrenches: Used for tightening the glands and fittings that secure the MICC cables.

(5b)
(i) Fire Resistance
(ii) High Temperature Rating
(iii) Mechanical Strength
(iv) Chemical Resistance
(v) Long lifespan
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(6a)
(i) Lightweight: Aluminium is lighter than copper, making it easier to handle and install in overhead applications. This can reduce the strain on support structures and make installation more efficient.

(ii) Cost-effective: Aluminium is generally more cost-effective than copper, making it a preferred choice for overhead installations where large quantities of conductor are required. It offers a good balance between performance and cost.

(iii) Good conductivity: While copper has higher electrical conductivity than aluminium, aluminium conductors are still capable of carrying electrical current effectively. Properly designed aluminium conductors can meet the electrical demands of overhead installations.

(iv) Corrosion resistance: Aluminium conductors have inherent corrosion resistance, making them suitable for outdoor overhead installations. They can withstand exposure to environmental elements without significant degradation.

(v) Expansion and contraction: Aluminium has a higher coefficient of thermal expansion compared to copper. This property allows aluminium conductors to accommodate temperature variations in overhead installations without the risk of damage.

(vi) Ease of Installation: Due to its lighter weight, aluminum conductors are generally easier to transport, handle, and install. This can lead to more efficient installation processes, especially in challenging terrains or remote locations.

(6b)
(i) Cross arm: A cross arm is a horizontal support structure made of wood or metal that is mounted on a utility pole. It provides a stable platform for attaching electrical conductors, insulators, and other equipment in overhead power distribution systems.

(ii) Stay wire: Stay wire, also known as guy wire, is a tensioned cable or wire that provides additional support and stability to utility poles or towers. It helps to prevent the pole from leaning or swaying due to external forces such as wind or tension from overhead conductors.

(iii) Stay installation: Stay installation refers to the process of installing stay wires or guy wires to reinforce the stability of utility poles or towers. This involves securely anchoring the wires to the ground or other stable structures to provide lateral support and prevent the pole from leaning or toppling over.

(iv) Disc installation: Disc installation refers to the mounting of insulator discs on cross arms or other support structures in overhead power distribution systems. Insulator discs are used to electrically isolate the conductors from the supporting structure and provide insulation to prevent electrical leakage.

(v) Cross arm bolt: A cross arm bolt is a type of fastener used to secure the cross arm to the utility pole. It is typically a threaded metal rod that passes through the cross arm and is tightened with nuts to ensure a secure attachment.
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PART III

(7)
(i) ASSEMBLE AN ELECTRIC GENERATOR:
(a) Start by gathering all the necessary components and tools required for assembly.

(b) Begin by placing the generator base or frame on a stable and level surface.

(c) Attach the engine to the base or frame according to the manufacturer’s instructions, ensuring proper alignment and secure fastening.

(d) Connect the fuel tank to the engine and make sure it is securely attached.

(e) Install the generator’s alternator or generator head, ensuring proper alignment and connection to the engine.

(f) Connect the electrical wiring, including the output terminals, control panel, and any necessary switches or circuit breakers.

(g) Install the air filter, oil filter, and any other required components according to the manufacturer’s instructions.

(h) Fill the engine with the recommended oil and fuel, following the manufacturer’s guidelines.

(i) Check all connections, tighten any loose bolts or fasteners, and ensure everything is properly secured.

(j) Finally, test the generator to ensure it is functioning correctly before putting it into regular use.

(ii) DISMANTLE AN ELECTRIC GENERATOR:
(a) Begin by disconnecting the generator from any power sources and turning it off.

(b) Allow the generator to cool down if it has been running.

(c) Disconnect any electrical connections, switches, or circuit breakers.

(d) Shut off the fuel supply and drain the fuel tank if necessary.

(e) Remove any air filters, oil filters, or other detachable components.

(f) Disconnect the generator head or alternator from the engine, following the manufacturer’s instructions.

(g) Detach the engine from the base or frame, ensuring proper handling and support.

(h) Clean and store all components in a safe and appropriate manner.

(i) If needed, consult the manufacturer’s guidelines for any additional steps or precautions specific to your generator model.
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(8a)
Lubricant is a substance, often in the form of a liquid or a semi-fluid, that is used to reduce friction between moving surfaces. It is applied to surfaces in contact to minimize wear and heat generation, thereby improving the efficiency and lifespan of machinery.

(8b)
(i) Bearings: Proper lubrication of bearings reduces friction and wear, enhancing the motor’s efficiency and extending its life.

(ii) Gears: If the motor has gears, they should be lubricated to reduce friction and ensure smooth meshing, preventing wear and noise.

(iii) Seals and O-rings: Lubrication helps maintain the integrity of seals and O-rings, preventing leaks and ensuring a proper seal.

(iv) Shafts and Bushings: Lubricating the motor shaft and bushings reduces friction and wear, allowing for smooth rotation.

(8c)
(i) Friction Reduction: Lubrication minimizes friction between moving parts, such as bearings and gears, reducing wear and heat generation.

(ii) Wear Prevention: Proper lubrication helps prevent wear on components, prolonging the lifespan of the motor.

(iii) Heat Dissipation: Lubricants aid in dissipating heat generated during motor operation, preventing overheating and maintaining optimal operating temperatures.

(iv) Efficiency Improvement: Reduced friction and wear contribute to improved motor efficiency, ensuring that the motor operates at its best performance.

(v) Noise Reduction: Lubrication helps in maintaining smooth and quiet motor operation by minimizing the noise associated with friction.

(vi) Seal Integrity: Lubrication helps in preserving the integrity of seals and O-rings, preventing the ingress of contaminants and maintaining a clean internal environment.
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(9)
(i) Motor Inspection:
Begin by inspecting the motor thoroughly. Check for any physical damage, contamination, or signs of overheating. Ensure that the motor housing is clean and free from debris.

(ii) Record Motor Data:
Record essential motor data such as the motor type, power rating, voltage, current, and speed. This information is crucial for selecting the appropriate wire gauge and insulation materials during the winding process.

(iii) Disconnect Power:
Disconnect the motor from the power source to ensure safety during the winding process. This may involve locking out and tagging out the power source.

(iv) Document Existing Winding Configuration:
Document the existing winding configuration, noting the number of turns, wire gauge, and the way the coils are connected. This information is essential for replicating the original winding pattern.

(v) Remove Old Winding:
Carefully remove the old winding from the motor. Take note of any specific winding techniques used in the original winding, such as layering or winding patterns.

(vi) Clean the Motor:
Thoroughly clean the motor to remove any dust, dirt, or contaminants that could affect the performance of the new winding. Cleaning is particularly important in preventing insulation issues.

(vii) Inspect Core and Stator:
Inspect the core and stator for any damage or wear. If there are issues, they should be addressed before proceeding with the winding process.

(viii) Prepare Insulation:
Prepare insulation materials, such as tapes and varnishes, to ensure proper insulation between windings and layers. Insulation is crucial for preventing short circuits.

(ix) Select Winding Method:
Choose the appropriate winding method based on the motor type and application. Common methods include random winding, lap winding, and wave winding.

(x) Prepare Winding Machine:
Set up the winding machine with the correct wire gauge and tension settings. Ensure that the machine is calibrated for the specific motor being wound.

(xi) Wind Coils:
Begin winding the coils according to the documented winding configuration. Pay close attention to the layering and connections between coils.

(xii) Insulate and Finish:
Insulate the coils as needed, using appropriate insulating materials. Ensure that the winding is secure and properly positioned within the motor. Finish the winding process by securing the end turns and making any necessary connections.