CSLB C-10 Electrical ContractorElectrical Theory and CalculationsMedium
A 208V, 3-phase pure resistive load draws 40 amps. What is the approximate total real power consumed by the load?
- A14.4 kW
- B20.8 kW
- C28.8 kW
- D8.3 kW
Show answer & explanationAnswer & explanation
Correct answer: A. 14.4 kW
For a pure resistive three-phase load, the power factor is 1. The real power (P) is calculated using the formula P = √3 * V * I. Multiply the square root of 3 by the voltage and current.
Why the other options are wrong
- B. This is a calculation error, possibly using a single-phase formula or incorrect constant.
- C. This value is too high, indicating a misapplication of the formula or incorrect units.
- D. This is a calculation error, possibly dividing by √3 or miscalculating.
Three-Phase Real Power (Resistive)
Real power in a three-phase purely resistive circuit is the actual power converted into useful work or heat. It is measured in Watts (W).
- Calculated as P = √3 * V * I (when PF=1).
- For resistive loads, power factor is always 1.
- Represents the average power over a cycle.
Memory trick: Real Power for Three-Phase is Root 3 times V I, if it's purely resistive!