CSLB C-10 Electrical ContractorElectrical Theory and CalculationsMedium
A three-phase motor operates on a 208V supply and draws 25 amps. If the motor has a power factor of 0.85, what is the approximate real power consumed by the motor?
- A9.1 kW
- B7.6 kW
- C8.5 kW
- D6.4 kW
Show answer & explanationAnswer & explanation
Correct answer: B. 7.6 kW
The real power (P) in a three-phase circuit is calculated using the formula P = √3 × V × I × PF. Substituting the given values: P = √3 × 208V × 25A × 0.85 = 7646.6 W, which is approximately 7.6 kW.
Why the other options are wrong
- A. This could be a calculation error or a misapplication of the formula.
- C. This is likely a result of omitting the power factor or square root of 3.
- D. This might result from incorrect use of the power factor or voltage in the calculation.
Three-Phase Real Power
The actual power consumed by a three-phase load, measured in watts (W) or kilowatts (kW), considering voltage, current, and power factor.
- Calculated as P = √3 × V × I × PF.
- Power factor (PF) accounts for reactive power.
- Represents the useful work done by the circuit.
Memory trick: Real Power is Root-3 times Voltage, Current, and Power Factor.