CHAPTER PAGE
1. Circuit Measurement
2. Circuit Protection Devices
3. Circuit Control Devices
APPENDIX
I. Glossary
II. Laws of Exponents
III. Schematic Symbols
IV. Cross Reference of Military and Commercial Fuse Designations
LEARNING OBJECTIVES
Learning objectives are stated at the beginning of each chapter. These learning objectives serve as a
preview of the information you are expected to learn in the chapter. The comprehensive check questions
are based on the objectives. By successfully completing the NRTC, you indicate that you have met the
objectives and have learned the information. The learning objectives are listed below.
Upon completion of this chapter you will be able to:
1. State two ways circuit measurement is used, why in-circuit meters are used, and one advantage of out-of-circuit meters.
2. State the way in which a compass reacts to a conducting wire including the compass reaction to increasing and decreasing dc and ac high and low frequencies.
3. State how a d’Arsonval meter movement reacts to dc.
4. State the purpose of a rectifier as used in ac meters.
5. State the meaning of the term "damping" as it applies to meter movements and describe two methods by which damping is accomplished.
6. Identify average value as the value of ac measured and effective value (rms) as the ac value indicated on ac meter scales.
7. Identify three meter movements that measure dc or ac without the use of a rectifier.
8. State the electrical quantity measured by an ammeter, the way in which an ammeter is connected in a circuit, and the effect of an ammeter upon a circuit.
9. Define ammeter sensitivity.
10. State the method used to allow an ammeter to measure different ranges and the reason for using the highest range when connecting an ammeter to a circuit.
11. List the safety precautions for ammeter use.
12. State the electrical quantity measured by a voltmeter, the way in which a voltmeter is connected
in a circuit, the way in which a voltmeter affects the circuit being measured, and the way in which a voltmeter is made from a current reacting meter movement.
13. Define voltmeter sensitivity.
14. State the method used to allow a voltmeter to measure different ranges and the reason for using the highest range when connecting a voltmeter to a circuit.
15. Identify the type of meter movement that reacts to voltage and the most common use of this movement.
16. List the safety precautions for voltmeter use.
17. State the electrical quantity measured by an ohmmeter, the second use of an ohmmeter, and the way in which an ohmmeter is connected to a resistance being measured.
18. State the method used to allow an ohmmeter to measure different ranges and the area of an ohmmeter scale that should be used when measuring resistance.
19. State the two types of ohmmeters and the way in which each can be identified.
20. List the safety precautions for ohmmeter use.
21. State the primary reason for using a megger and the method of using it.
22. Identify normal and abnormal indications on a megger.
23. List the safety precautions for megger use.
24. State how a multimeter differs from other meters, the reason a multimeter is preferred over separate meters, and the way in which a multimeter is changed from a voltage measuring device to a current measuring device.
25. State the reason the ac and dc scales of a multimeter differ, the reason for having a mirror on the scale of a multimeter, and the proper way of reading a multimeter using the mirror.
26. List the safety precautions for multimeter use.
27. State the purpose of a hook-on type voltameter.
28. State the electrical quantity measured by a wattmeter and a watt-hour meter.
29. Identify the two types of frequency meters.
30. Identify the type of meter and interpret the meter reading from scale presentations of an ammeter;a voltmeter; an ohmmeter; a megger; a multimeter (current, voltage, and resistance examples); awattmeter; a watt-hour meter; and a frequency meter (vibrating reed and moving-disk types)
Introduction to Circuit Protection, Control, and Measurement
Circuit protection, control, and measurement are essential aspects of electrical engineering that ensure the safety, reliability, and efficiency of electrical systems. These components play critical roles in preventing damage, controlling electrical power, and monitoring system performance.
1. Circuit Protection
Circuit protection refers to the devices and methods used to safeguard electrical circuits from damage due to excessive current, voltage spikes, or short circuits. The main objective is to prevent overheating, fires, and damage to electrical components and equipment.
Key Circuit Protection Devices:
Fuses: A fuse is a simple protection device that consists of a metal wire or strip that melts when too much current flows through it, breaking the circuit. Fuses are inexpensive and are used in many household and automotive applications. However, they need to be replaced once they blow.
Circuit Breakers: Circuit breakers are automatic switches that interrupt the flow of current when an overload or short circuit is detected. Unlike fuses, circuit breakers can be reset manually after tripping, making them reusable and convenient for use in electrical panels.
Surge Protectors: These devices protect electrical equipment from voltage spikes, which can be caused by lightning strikes or power surges. Surge protectors divert excess voltage away from sensitive components, preventing damage.
Ground Fault Circuit Interrupters (GFCIs): GFCIs are designed to protect against electrical shock by detecting ground faults (leakage currents) and interrupting the circuit. They are commonly used in wet or damp environments, such as bathrooms and kitchens.
Arc Fault Circuit Interrupters (AFCIs): AFCIs detect hazardous electrical arcs (which can lead to fires) and interrupt the circuit to prevent potential fire hazards. They are typically used in residential wiring to enhance safety.
Importance of Circuit Protection:
- Prevents Damage: Protects electrical components and devices from damage due to excessive current or voltage.
- Enhances Safety: Reduces the risk of electrical fires, equipment failure, and electrical shock.
- Increases System Reliability: Ensures the stable operation of electrical systems by minimizing the impact of faults.
2. Circuit Control
Circuit control involves devices and methods used to manage the flow of electrical power within a circuit. Control components are essential for starting, stopping, adjusting, and directing electrical currents in various applications.
Key Circuit Control Devices:
Switches: Switches are the most basic control devices, used to manually open or close a circuit. They come in various types, including toggle switches, push-button switches, and rotary switches.
Relays: Relays are electrically operated switches that use an electromagnetic coil to open or close a circuit. They are commonly used for remote control and automation purposes, such as in automotive systems and industrial machinery.
Contactors: Contactors are heavy-duty relays designed to handle high-power loads. They are used to control large electric motors, heating systems, and lighting in industrial applications.
Dimmer Switches and Variable Resistors: These devices control the amount of current flowing through a circuit, allowing for the adjustment of brightness in lighting or the speed of a motor.
Programmable Logic Controllers (PLCs): PLCs are specialized computers used to control complex industrial processes. They receive inputs from sensors, process the data, and send outputs to control devices, automating tasks and increasing efficiency.
Importance of Circuit Control:
- Precision and Flexibility: Enables precise control over electrical devices, enhancing performance and efficiency.
- Automation: Facilitates automated processes in industries, reducing the need for manual intervention and increasing productivity.
- Safety: Provides control over electrical systems, allowing for emergency shutdowns and the prevention of dangerous conditions.
3. Circuit Measurement
Circuit measurement involves the use of instruments to monitor and evaluate the electrical parameters of a circuit. Accurate measurements are crucial for diagnosing issues, ensuring proper operation, and maintaining system performance.
Key Circuit Measurement Instruments:
Multimeters: Multimeters are versatile tools used to measure voltage (AC and DC), current, and resistance in electrical circuits. They can also test continuity, capacitance, and diode functionality, making them essential for troubleshooting.
Oscilloscopes: Oscilloscopes are devices used to visualize electrical signals over time. They display waveforms of voltage and current, helping to analyze the frequency, amplitude, and shape of signals in complex circuits.
Clamp Meters: Clamp meters are used to measure current without making direct contact with the conductor. The clamp mechanism allows for quick and safe current measurement, especially in high-voltage applications.
Ammeters and Voltmeters: Ammeters measure the current flowing through a circuit, while voltmeters measure the voltage across two points. Both are commonly used in electrical panels and testing equipment.
Wattmeters: Wattmeters measure the power consumption of electrical devices, helping to monitor energy usage and efficiency. They are used in power management systems and energy audits.
Importance of Circuit Measurement:
- Diagnostics: Helps identify faults, such as open circuits, short circuits, or component failures, enabling quick repairs.
- Performance Monitoring: Ensures that electrical systems are operating within specified parameters, preventing damage and downtime.
- Optimization: Assists in optimizing the performance of electrical systems by providing accurate data for adjustments and improvements.
4. Integration of Circuit Protection, Control, and Measurement
In modern electrical systems, circuit protection, control, and measurement work together to ensure safety, efficiency, and reliability:
- Control systems use switches, relays, and PLCs to manage the flow of electricity and automate processes.
- Protection devices such as fuses, circuit breakers, and surge protectors safeguard these systems from faults and hazards.
- Measurement tools provide feedback and data, allowing operators to monitor system performance and make necessary adjustments.
For example, in an industrial setting, a PLC may control the operation of a motor. Circuit breakers protect the motor from overloads, and sensors measure the current and voltage to ensure everything is functioning correctly. This integration is essential for the smooth and safe operation of electrical systems.
Conclusion
Circuit protection, control, and measurement are integral components of any electrical system, from simple household circuits to complex industrial networks. By ensuring that circuits are protected from faults, effectively controlled, and accurately measured, these elements contribute to the overall safety, efficiency, and reliability of electrical systems. Understanding these concepts is fundamental for anyone involved in the design, maintenance, and operation of electrical systems, as they help prevent equipment damage, enhance performance, and reduce risks.
