If you see two different values on an appliance's label — one in watts (W) and another in volt-amperes (VA) — you're not looking at a printing error. This is a real and important difference, especially for appliances containing motors or transformers.
Real power: what is actually converted into useful work
Real power, in watts (W), is the energy that the appliance actually converts into useful work — heat, motion, light. This is the number that determines your actual consumption in kilowatt-hours, which you're billed for.
Apparent power: what the power source "sees"
Apparent power, in volt-amperes (VA), is the product of the voltage and the total current the appliance draws from the network — regardless of how much of it is actually converted into useful work. In "simple," purely resistive loads (such as a heater or an incandescent bulb), real and apparent power are very close. But in loads containing coils and motors (air conditioner, refrigerator, washing machine, fan), the appliance draws more current from the network than what's actually converted into useful work — and the difference between them is expressed by what's called the "power factor."
Why does this matter to you in practice?
The supply wire and breaker handle the total current drawn by the appliance (related to apparent power), while your meter usually bills you based on actual energy consumed. For this reason, when calculating breaker or wire capacity for a circuit feeding motor-driven appliances (such as multiple air conditioners), it's not enough to simply add up the printed wattage values — the actual current drawn may be higher than what dividing the watts by the voltage directly would suggest.
The power factor is a value between zero and one. Purely resistive loads (heaters, incandescent bulbs) have a power factor close to 1 (the two values are close). Loads with motors and coils have a power factor less than 1, so their apparent power is higher than their real power for the same level of useful consumption.
Sample answer: Real power (watts) is the energy the appliance actually converts into useful work (heat, motion, light), and it's what you're billed for on your electricity bill. Apparent power (volt-amperes) is the product of the voltage and the total current drawn from the network, regardless of how much converts into useful work. In purely resistive loads the two values are close, but in appliances with motors and coils (air conditioners, refrigerators), the appliance draws more current from the network compared to its actual useful energy, so its apparent power is higher than its real power — and the ratio between them is called the power factor.
Calculating the expected total current on a circuit feeding motor-driven appliances (such as several air conditioners) by simply dividing the printed wattage value by the voltage. This ignores the power factor, and may lead to underestimating the actual current drawn, which affects the accuracy of selecting the wire size and breaker rating for this circuit.
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