API-SIEE Exam - Topic 5 Question 7 Discussion

The correct answer isCbecauseapparent powerin an AC electrical system is measured involt-amperes VA. Apparent power represents the total electrical power supplied to a circuit and is the combination ofreal powerandreactive power. Real power, which performs useful work such as turning a motor shaft or producing heat, is measured inwatts. Reactive power, which supports magnetic and electric fields in inductive or capacitive equipment, is measured invars. Apparent power is therefore the vector sum of these two and is expressed inVAor larger units such askVAandMVA.

The other options are incorrect for this reason.Mhosis a unit of conductance, not power.Varsmeasure reactive power only.Wattsmeasure true or active power only. In source inspection and quality surveillance of electrical equipment, understanding these distinctions is important when reviewing motor data sheets, transformer ratings, switchgear load data, and electrical test reports. Equipment such as transformers and generators are commonly rated inkVA or MVAbecause their thermal and current-carrying capability is tied toapparent power, makingvolt-amperesthe correct answer.