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Why companies rate UPS in VAs and PSUs in Watts

Almost everyone who has went to buy power equipment such as a power supply and UPS has assuredly noticed that while power supply units are rated in Watts, UPS systems are rated in VA or in both VA and Watts. This usually leads to confusion as most people not only lack the technical knowledge to understand the difference between VA and Watt units but few might even realize that there is a difference.

Even less realize that not only VAs and Watts are different but there is even a third “type” of power, VA reactive or VArs. In this article we will try and explain in layman's terms the difference between the three types of power so people with basic skills and knowledge can understand.

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5 comments

  1. Great read, I found this easier to understand when compared with the first one last week.

  2. that helps clear up some things for me, thanks!

  3. Got lost a few times, but for the most parts, thumbs up !

  4. When you say that reactive power does not move any energy, you are wrong. In reality, the reactive power is generated by any coil or capacity and is “send” back to the power plant, adding extra current to the power line. This is the correct way to explain reactive power.

  5. Definition of Energy : The capacity of a system to *perform work*. Reactive power moves no energy because, like you said yourself, it is being returned to the power plant. 99% of the equipment does not make any use of it. You’re confusing current and/or power with energy, energy has an entirely different meaning.