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State four IEE regulations requirements regarding P.M.E systems. (4 marks)craft1 electrical June/July 2020
PME systems must be designed, installed, and maintained in accordance with BS 7671:2018 (IET Wiring Regulations). PME systems must be able to safely conduct the maximum prospective fault current that could occur in the system. PME systems must have an earth fault loop impedance that is low enough toRead more
- PME systems must be designed, installed, and maintained in accordance with BS 7671:2018 (IET Wiring Regulations).
- PME systems must be able to safely conduct the maximum prospective fault current that could occur in the system.
- PME systems must have an earth fault loop impedance that is low enough to ensure that the disconnection time for a fault does not exceed the maximum values specified in BS 7671.
- PME systems must have a fault current indicator to indicate when a fault has occurred.
- PME systems must have a means of testing to ensure that the system is functioning correctly.
- PME systems must be regularly inspected and tested to ensure that they are in good working order.
See lessState three advantages of MCBs over fuses .craft1 electrical June/July 2020
Resettable: MCBs can be reset after tripping, while fuses must be replaced. This makes MCBs more convenient and cost-effective to use. More sensitive: MCBs are more sensitive to abnormal current conditions, and can trip at lower levels of overcurrent than fuses. This makes them more effective at proRead more
- Resettable: MCBs can be reset after tripping, while fuses must be replaced. This makes MCBs more convenient and cost-effective to use.
- More sensitive: MCBs are more sensitive to abnormal current conditions, and can trip at lower levels of overcurrent than fuses. This makes them more effective at protecting electrical circuits from damage.
- Higher interrupting capacity: MCBs can interrupt higher levels of current than fuses, making them suitable for use in larger electrical systems.
- More precise: MCBs can be rated for specific levels of current, allowing for more precise protection of electrical circuits.
- Longer lifespan: MCBs have a longer lifespan than fuses, as they can be reset and do not need to be replaced as frequently.
See lessExplain the effects of each of the following faults in electrical installations: (i) sustained overloading of wiring and equipment, (ii) faulty contacts and connections. (4 marks) craft1 electrical June/July 2020
(i) Sustained overloading of wiring and equipment: When wiring and equipment are subjected to sustained overloading, they can become damaged due to the excess heat generated by the increased current flow. This can cause insulation to break down and potentially lead to electrical fires. The electricaRead more
(i) Sustained overloading of wiring and equipment: When wiring and equipment are subjected to sustained overloading, they can become damaged due to the excess heat generated by the increased current flow. This can cause insulation to break down and potentially lead to electrical fires. The electrical system may also become less efficient and may not function correctly.
(ii) Faulty contacts and connections: Faulty contacts and connections can cause a number of problems in an electrical installation. They can result in high resistance, which can cause heat generation and potentially lead to electrical fires. They can also cause voltage drops, leading to poor performance of electrical equipment and possibly damaging it. In addition, faulty contacts and connections can lead to intermittent power supply and equipment failure.
See lessOutline three tests carried out in electrical machines. (3 marks)craft1 electrical June/July 2020
No-load test: This test is used to measure the no-load current, no-load power, and no-load loss of an electrical machine. It is performed by running the machine without any load, and measuring the current and power consumption at rated voltage and frequency. Load test: This test is used to measure tRead more
- No-load test: This test is used to measure the no-load current, no-load power, and no-load loss of an electrical machine. It is performed by running the machine without any load, and measuring the current and power consumption at rated voltage and frequency.
- Load test: This test is used to measure the performance of an electrical machine under load. It is performed by applying a load to the machine and measuring the current, voltage, power, and efficiency at various load points.
- Short-circuit test: This test is used to determine the short-circuit current and impedance of an electrical machine. It is performed by short-circuiting the machine and measuring the resulting current.
- Insulation resistance test: This test is used to measure the resistance of the insulation in an electrical machine. It is performed by applying a voltage to the machine and measuring the resulting current.
- Temperature rise test: This test is used to measure the temperature rise of an electrical machine under load. It is performed by applying a load to the machine and measuring the temperature at various points on the machine.
See lessList four types of D.C motors. (4 marks)craft1 electrical June/July 2020
Series DC motor: A series DC motor has a high starting torque and is able to operate at high speeds. However, it is less efficient than other types of DC motors and is not commonly used. Shunt DC motor: A shunt DC motor has a relatively low starting torque and is able to operate at a wide range of sRead more
- Series DC motor: A series DC motor has a high starting torque and is able to operate at high speeds. However, it is less efficient than other types of DC motors and is not commonly used.
- Shunt DC motor: A shunt DC motor has a relatively low starting torque and is able to operate at a wide range of speeds. It is more efficient than a series DC motor and is commonly used in applications that require precise speed control.
- Compound DC motor: A compound DC motor has a combination of series and shunt winding on the stator, which allows it to have a higher starting torque and better speed control than a pure series or shunt motor.
- Permanent magnet DC motor: A permanent magnet DC motor has permanent magnets on the stator, which provides the magnetic field required for operation. This type of motor has a high starting torque and is able to operate at high speeds, but is less efficient than other types of DC motors.
- Brushed DC motor: A brushed DC motor has a set of brushes that make contact with the rotor and supply the electrical current required for operation. This type of motor is simple and inexpensive, but has a lower efficiency and a shorter lifespan than other types of DC motors.
- Brushless DC motor: A brushless DC motor has no brushes and relies on electronic commutation to supply the electrical current to the rotor. This type of motor is more efficient and has a longer lifespan than a brushed DC motor, but is more expensive and requires more complex electronics to control.
See lessState three merits of mineral insulated metal sheathed cables.craft1 electrical June/July 2020
Durability: MIMS cables are extremely durable and resistant to physical damage, due to the metal sheath that protects the inner conductor. This makes them well-suited for use in harsh environments or in applications where the cables are subject to physical abuse. Fire resistance: MIMS cables are higRead more
- Durability: MIMS cables are extremely durable and resistant to physical damage, due to the metal sheath that protects the inner conductor. This makes them well-suited for use in harsh environments or in applications where the cables are subject to physical abuse.
- Fire resistance: MIMS cables are highly resistant to fire and are able to maintain their structural integrity even in the presence of high temperatures. This makes them ideal for use in fire-critical applications, such as in buildings or in electrical systems that are required to have a high level of fire resistance.
- High temperature resistance: MIMS cables are able to operate at high temperatures and have a high temperature rating, making them suitable for use in high temperature environments or for carrying high-temperature electrical circuits.
See lessState three methods of soldering cable joints.craft1 electrical June/July 2020
Soldering iron: This method involves using a soldering iron to heat the joint and apply a soldering wire or rod to create a strong, electrical connection. Soldering gun: This method is similar to using a soldering iron, but uses a soldering gun instead. Soldering guns are typically more powerful thaRead more
- Soldering iron: This method involves using a soldering iron to heat the joint and apply a soldering wire or rod to create a strong, electrical connection.
- Soldering gun: This method is similar to using a soldering iron, but uses a soldering gun instead. Soldering guns are typically more powerful than soldering irons and are better suited for soldering large, thick cables.
- Induction soldering: This method involves using an induction coil to generate heat in the joint, which is then used to melt the solder and create a connection.
- Resistance soldering: This method involves using an electrical current to generate heat in the joint, which is then used to melt the solder and create a connection.
- Ultrasonic soldering: This method involves using high-frequency vibrations to generate heat in the joint, which is then used to melt the solder and create a connection.
- Laser soldering: This method involves using a focused laser beam to generate heat in the joint, which is then used to melt the solder and create a connection.
See lessState any three types of cable joints.craft1 electrical June/July 2020
Crimp joints: Crimp joints are made by inserting the cable into a connector and then using a crimping tool to apply pressure to the connector, which secures the cable in place and creates an electrical connection. Solder joints: Solder joints are made by heating a solder wire or rod and applying itRead more
- Crimp joints: Crimp joints are made by inserting the cable into a connector and then using a crimping tool to apply pressure to the connector, which secures the cable in place and creates an electrical connection.
- Solder joints: Solder joints are made by heating a solder wire or rod and applying it to the joint, which creates a strong, electrical connection.
- Compression joints: Compression joints are made by inserting the cable into a connector and then using a compression tool to apply pressure to the connector, which secures the cable in place and creates an electrical connection.
- Twist-on joints: Twist-on joints are made by inserting the cable into a connector and then using a twisting motion to secure the cable in place and create an electrical connection.
- Screw joints: Screw joints are made by inserting the cable into a connector and then tightening a screw to secure the cable in place and create an electrical connection.
- Splice joints: Splice joints are made by physically splicing two or more cables together and securing them with tape, insulation, or a splice connector.
See lessExplain each of the following terms as used in cable size calculations: (i) ambient temperature; (ii) voltage drop
(i) Ambient temperature: Ambient temperature refers to the temperature of the surrounding environment in which a cable is installed. This is an important factor to consider when selecting a cable, as the temperature rating of the cable should be equal to or higher than the ambient temperature to ensRead more
(i) Ambient temperature: Ambient temperature refers to the temperature of the surrounding environment in which a cable is installed. This is an important factor to consider when selecting a cable, as the temperature rating of the cable should be equal to or higher than the ambient temperature to ensure that the cable can operate safely.
(ii) Voltage drop: Voltage drop refers to the decrease in voltage that occurs along the length of a cable as a result of resistance in the conductor. Voltage drop can be a concern in long-distance or high-power applications, as it can reduce the efficiency of the system and cause the voltage at the load to be lower than the voltage at the source. To minimize voltage drop, it is important to choose a cable with a low resistance and to use a sufficiently large cross-sectional area to carry the required current.
See lessOutline three LEE regulations regarding cable runs. (3 marks)craft1 electrical June/July 2020
The IEE (Institution of Electrical Engineers) is a professional organization that sets standards and guidelines for electrical engineering practice in the UK. Here are three IEE regulations regarding cable runs: Maximum voltage drop: The IEE Wiring Regulations (BS 7671) specify a maximum allowable vRead more
The IEE (Institution of Electrical Engineers) is a professional organization that sets standards and guidelines for electrical engineering practice in the UK. Here are three IEE regulations regarding cable runs:
- Maximum voltage drop: The IEE Wiring Regulations (BS 7671) specify a maximum allowable voltage drop for different types of cables and applications. This is to ensure that the voltage at the load is sufficient to operate the equipment and to prevent losses in efficiency due to excessive voltage drop.
- Cable tray fill: The IEE Wiring Regulations specify a maximum fill ratio for cable trays, which is the ratio of the total cross-sectional area of the cables in the tray to the cross-sectional area of the tray itself. This is to ensure that the cables have sufficient space to dissipate heat and to prevent overheating and damage to the cables.
- Cable bending radius: The IEE Wiring Regulations specify minimum bending radii for different types of cables, which is the minimum radius that a cable can be bent without damaging the insulation or causing undue stress on the conductor. This is to ensure that the cables are installed safely and will not fail due to improper bending.
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