CSLB C-10 Electrical ContractorElectrical Theory and CalculationsMedium
A client is planning to install a new induction motor that will operate at 208V, three-phase, drawing 45 amps with a power factor of 0.8 lagging. What is the approximate apparent power for this motor?
- A10.4 kVA
- B8.1 kVA
- C16.2 kVA
- D20.8 kVA
Show answer & explanationAnswer & explanation
Correct answer: C. 16.2 kVA
Apparent power (S) in a three-phase system is calculated using the formula S = √3 * V * I. The power factor is not needed for calculating apparent power directly from voltage and current.
Why the other options are wrong
- A. This is likely a calculation error, possibly using an incorrect constant.
- B. This might be a calculation for real power or a single-phase calculation.
- D. This value is too high, indicating a misapplication of the formula or incorrect units.
Three-Phase Apparent Power
Apparent power in a three-phase system is the total power that appears to be supplied to the circuit, including both real and reactive power. It is measured in Volt-Amperes (VA).
- Calculated as S = √3 * V * I.
- It is the hypotenuse of the power triangle.
- Represents the total power the source must supply.
Memory trick: Apparent Power is Always the Biggest, like an 'S'uperhero.