By the end of this chapter, you will be able to:
Mastering these skills will help you understand and solve real electrical problems confidently and safely in your trade.
Electrical principles are fundamental to the refrigeration and air conditioning (RAC) industry, where understanding electrical quantities is crucial for system design, troubleshooting, and maintenance. Professionals in Kenya's RAC sector must be proficient in interpreting and applying these quantities to ensure safe and efficient operation of equipment. This chapter introduces the basic electrical quantities and their measurement units, focusing on the International System of Units (SI units), which standardizes electrical measurements globally and locally.
The International System of Units (SI) provides a universal standard for measuring electrical quantities. For RAC professionals in Kenya, SI units ensure consistency in calculations, equipment specifications, and communication with manufacturers and regulatory bodies. Understanding SI units is essential for accurate measurement of voltage, current, resistance, power, and energy in refrigeration and air conditioning systems.
The SI unit system is a globally accepted decimal-based system used for scientific and engineering measurements. It simplifies electrical calculations and ensures uniformity across different regions and industries, including Kenya's RAC sector.
Electrical quantities are measured using base and derived SI units. The base units serve as the foundation, while derived units combine base units to express complex electrical properties.
SI prefixes modify base units to express very large or very small quantities conveniently. RAC professionals often encounter these prefixes in equipment ratings and measurements.
In RAC systems, SI units are used to specify electrical parameters for design, maintenance, and safety checks. Understanding and applying these units correctly is essential for Kenyan technicians and engineers.
Convert the following electrical quantities into base SI units: 5 kW, 250 mA, 3 μF. (6 marks)
A compressor motor operates at 220 V and draws a current of 10 A. Express the voltage and current using appropriate SI prefixes. (4 marks)
Calculate the resistance of a coil if the voltage across it is 110 V and the current is 5 A. Express the resistance in ohms. (6 marks)
An air conditioning unit consumes 1.5 kW of power. Express this power in watts and megawatts. (4 marks)
A capacitor in an RAC circuit has a capacitance of 4 μF. Convert this capacitance into farads. (3 marks)
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Create a free accountThis chapter introduced the International System of Units (SI) as the standard framework for measuring electrical quantities, ensuring consistency and clarity in calculations. It detailed the SI units for various electrical parameters such as current, voltage, resistance, and power, establishing a clear understanding of their measurement. The chapter then explained Ohm's law, highlighting the fundamental relationship between voltage, current, and resistance in electrical circuits. Following this, it covered calculations involving these parameters, demonstrating how to determine power, current, voltage, and resistance in practical contexts. Lastly, the chapter described the instruments used to measure electrical quantities, including ammeters, voltmeters, and ohmmeters, emphasizing their roles in accurate electrical measurement and analysis. Together, these topics provide a comprehensive foundation for understanding and working with basic electrical principles.
Type: Individual
| Tools & Equipment | Materials |
|---|---|
| Multimeter | A3 size SI units reference charts |
| Calculator | Safety goggles |
| Pen and notebook | Dust coat overall |
| S/N | Item | Quantity |
|---|---|---|
| 1 | Multimeter | 1 Pc per Candidate |
| 2 | A3 size SI units reference charts | 1 Pc per Candidate |
| 3 | Calculator | 1 Pc per Candidate |
| 4 | Pen and notebook | 1 set per Candidate |
| 5 | Safety goggles | 1 Pair per Candidate |
| 6 | Dust coat overall | 1 Pc per Candidate |
| Items to be Evaluated | Marks Available | Marks Obtained | Comments |
|---|---|---|---|
| TASK 1: Preparation and Safety | |||
| Wore appropriate PPE including dust coat overall and safety goggles (Award 1 mark for correct PPE worn or zero) | 1 | ||
| Handled tools and equipment safely and correctly (Award 1 mark each for safe and correct use of multimeter and handling of charts) | 2 | ||
| Sub-Total | 3 | ||
| TASK 2: Identification of SI Units | |||
| Correctly identified and labeled SI unit for Voltage (Volt) (Award 2 marks for correct identification and labeling or zero) | 2 | ||
| Correctly identified and labeled SI unit for Current (Ampere) (Award 2 marks for correct identification and labeling or zero) | 2 | ||
| Correctly identified and labeled SI unit for Resistance (Ohm) (Award 2 marks for correct identification and labeling or zero) | 2 | ||
| Correctly identified and labeled SI unit for Power (Watt) (Award 2 marks for correct identification and labeling or zero) | 2 | ||
| Correctly identified and labeled SI unit for Capacitance (Farad) (Award 2 marks for correct identification and labeling or zero) | 2 | ||
| Sub-Total | 10 | ||
| TASK 3: Practical Measurement and Application | |||
| Used multimeter to measure voltage and recorded value with correct SI unit (Award 2 marks for correct measurement and SI unit or zero) | 2 | ||
| Used multimeter to measure current and recorded value with correct SI unit (Award 2 marks for correct measurement and SI unit or zero) | 2 | ||
| Used multimeter to measure resistance and recorded value with correct SI unit (Award 2 marks for correct measurement and SI unit or zero) | 2 | ||
| Sub-Total | 6 | ||
| TASK 4: Housekeeping and Reporting | |||
| Cleaned and returned tools and equipment to designated places (Award 1 mark for proper housekeeping or zero) | 1 | ||
| Prepared a brief report listing electrical parameters and their SI units (Award up to 3 marks based on completeness and accuracy of report) | 3 | ||
| Sub-Total | 4 | ||
| PRODUCT CHECKLIST | |||
| All electrical parameters correctly labeled with appropriate SI units on the chart (Award 5 marks for full correct labeling or zero) | 5 | ||
| Measurement values recorded with correct SI units and consistent accuracy (Award 5 marks for accurate measurements and correct units or zero) | 5 | ||
| Sub-Total | 10 | ||
| GRAND TOTAL | 33 | ||
Type: Individual
| Tools & Equipment | Materials |
|---|---|
| Digital Multimeter | Resistor 100 Ω ±5% |
| Connecting Wires with Crocodile Clips | Safety Goggles |
| Breadboard | Dust Coat Overall |
| DC Power Supply 12V | Insulated Gloves |
| S/N | Item | Quantity |
|---|---|---|
| 1 | DC Power Supply 12V | 1 Pc per Candidate |
| 2 | Resistor 100 Ω ±5% | 1 Pc per Candidate |
| 3 | Connecting Wires with Crocodile Clips | 3 Pcs per Candidate |
| 4 | Digital Multimeter | 1 Pc per Candidate |
| 5 | Breadboard | 1 Pc per Candidate |
| 6 | Safety Goggles | 1 Pair per Candidate |
| 7 | Dust Coat Overall | 1 Pc per Candidate |
| 8 | Insulated Gloves | 1 Pair per Candidate |
| Items to be Evaluated | Marks Available | Marks Obtained | Comments |
|---|---|---|---|
| TASK 1: Safety and Preparation | |||
| Wore safety goggles, dust coat overall, and insulated gloves before starting work (Award 1 mark if all PPE worn correctly, else 0) | 1 | ||
| Handled tools and equipment according to safety procedures (Award 1 mark for correct and safe use, else 0) | 1 | ||
| Sub-Total | 2 | ||
| TASK 2: Circuit Construction | |||
| Identified and gathered all required components and tools (Award 1 mark for correct identification and gathering, else 0) | 1 | ||
| Connected the 100 Ω resistor correctly on the breadboard (Award 2 marks if resistor placed correctly with secure connections, else 0) | 2 | ||
| Connected the DC power supply (12V) and wiring properly without loose connections (Award 2 marks if connections are correct and secure, else 0) | 2 | ||
| Sub-Total | 5 | ||
| TASK 3: Measurement and Verification | |||
| Measured voltage across the resistor using digital multimeter correctly (Award 2 marks for correct measurement method and accurate reading, else 0) | 2 | ||
| Measured current through the circuit correctly using digital multimeter (Award 2 marks for correct ammeter connection and reading, else 0) | 2 | ||
| Measured resistance of the resistor directly using digital multimeter (Award 1 mark for correct resistance measurement, else 0) | 1 | ||
| Recorded all measurements accurately (Award 1 mark for proper recording of values, else 0) | 1 | ||
| Calculated and verified that voltage equals current multiplied by resistance (V=IR) within ±5% tolerance (Award 3 marks for correct calculation and verification, else 0) | 3 | ||
| Sub-Total | 9 | ||
| TASK 4: Housekeeping and Reporting | |||
| Switched off and disconnected all equipment safely after completion (Award 1 mark for safe shutdown and disconnection, else 0) | 1 | ||
| Returned tools and materials to designated places (Award 1 mark for proper storage, else 0) | 1 | ||
| Cleaned the work area and disposed of any waste according to OSH guidelines (Award 1 mark for good housekeeping, else 0) | 1 | ||
| Prepared and submitted a brief report on the experiment and results (Award 3 marks for clear, concise report including measurements and conclusion, else 0) | 3 | ||
| Sub-Total | 6 | ||
| PRODUCT CHECKLIST | |||
| Circuit constructed correctly with firm connections and proper layout on breadboard (Award 3 marks for correct and neat assembly, else 0) | 3 | ||
| Measured voltage is approximately 12V across the resistor ±5% (Award 2 marks if measurement within tolerance, else 0) | 2 | ||
| Measured current corresponds to Ohm's law given the resistor value and supply voltage ±5% (Award 3 marks if current measurement matches theory within tolerance, else 0) | 3 | ||
| Measured resistance is within the resistor tolerance (100 Ω ±5%) (Award 2 marks if resistance value is within tolerance, else 0) | 2 | ||
| Sub-Total | 10 | ||
| GRAND TOTAL | 32 | ||
At the start of this chapter we promised you would be able to:
Tick each one you can genuinely do.
So, are you there yet?
You're competent when you can confidently do 50% or more of what this chapter promised.
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