Podcast
Questions and Answers
What is the primary purpose of derating factor calculations?
What is the primary purpose of derating factor calculations?
- To select the appropriate cable size for a specific application
- To determine the maximum voltage drop in a cable
- To calculate the short circuit current capacity of a cable
- To evaluate the thermal endurance of a cable (correct)
Which of the following is NOT a type of calculation that involves derating factors?
Which of the following is NOT a type of calculation that involves derating factors?
- Voltage drop calculations
- Thermal endurance calculations
- Short circuit current calculations
- Cable sizing calculations (correct)
What is the relationship between derating factors and cable catalogue data?
What is the relationship between derating factors and cable catalogue data?
- Derating factors are independent of cable catalogue data
- Derating factors are used to interpolate cable catalogue data
- Derating factors are used to extrapolate cable catalogue data
- Derating factors are obtained from cable catalogue data (correct)
In which type of calculation is the derating factor used to adjust the maximum permissible current?
In which type of calculation is the derating factor used to adjust the maximum permissible current?
What is the term for the test that evaluates the thermal endurance of a cable?
What is the term for the test that evaluates the thermal endurance of a cable?
What happens when the cable length increases?
What happens when the cable length increases?
What is the result of exceeding the maximum allowed voltage drop?
What is the result of exceeding the maximum allowed voltage drop?
What is the purpose of calculating voltage drop in a circuit?
What is the purpose of calculating voltage drop in a circuit?
What is the effect of increased current on the voltage drop?
What is the effect of increased current on the voltage drop?
What is the significance of the voltage drop limit in a circuit?
What is the significance of the voltage drop limit in a circuit?
What happens when the voltage drop is within the specified limits?
What happens when the voltage drop is within the specified limits?
What percentage of the voltage drop is typically allocated to the main transformer or main power supply?
What percentage of the voltage drop is typically allocated to the main transformer or main power supply?
How is the length of a cable typically calculated?
How is the length of a cable typically calculated?
What is the purpose of adding 5 meters to the measured length of a cable?
What is the purpose of adding 5 meters to the measured length of a cable?
What are the two methods used to calculate voltage drop from the source to the load?
What are the two methods used to calculate voltage drop from the source to the load?
What percentage of the voltage drop is typically allocated to the distribution board?
What percentage of the voltage drop is typically allocated to the distribution board?
What is the main reason for calculating voltage drop in electrical systems?
What is the main reason for calculating voltage drop in electrical systems?
What is the unit of measurement for the voltage drop calculation parameter mv/a/m?
What is the unit of measurement for the voltage drop calculation parameter mv/a/m?
In a voltage drop calculation, what is the purpose of dividing the calculated value by the operating voltage?
In a voltage drop calculation, what is the purpose of dividing the calculated value by the operating voltage?
What is the formula for calculating the voltage drop in parallel cables?
What is the formula for calculating the voltage drop in parallel cables?
What is the value by which the calculated voltage drop is multiplied to obtain a percentage value?
What is the value by which the calculated voltage drop is multiplied to obtain a percentage value?
What is the operating voltage used in the calculation of the voltage drop percentage?
What is the operating voltage used in the calculation of the voltage drop percentage?
Study Notes
Derating Factor
- Derating factors are obtained from cable catalogues
- Derating factor calculations involve:
- Voltage drop calculations
- Short circuit current calculations
- Thermal endurance tests for cables
Voltage Drop Calculations
- Voltage drop increases with cable length and resistance
- High voltage drop can cause load problems, reduced lighting levels, and motor starting difficulties
- Voltage drop limits are specified in a table
- In design, voltage drop is allocated as:
- 2% from the transformer or main supply to the distribution board
- 3% from the distribution board to the farthest point in the circuit
- Cable length is calculated by measuring horizontal cable runs, adding 5m as a safety margin, and considering vertical heights in the building
- Voltage drop can be calculated using:
- Direct calculation method
- Spreadsheet method (Sheets)
- Formula for voltage drop calculation:
- (mv/a/m) x L x I / 380 (or 400) x 100
- For parallel cables, the calculation is divided by the number of cables
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Description
This quiz assesses your understanding of derating factor calculations, including voltage drop and short circuit current calculations, as per cable catalogues.
