nuclear energy1 Why UPS systems are rated in VAs and PSUs in Watts; Explaining Watts, VAr and VA

When shopping for an uninterruptible power supply (UPS), almost everyone would have noticed that they are either rated in VA's only or in both VA's and Watt's. This is not so with the vast majority of household equipment, including the very power supply unit (PSU) of the computer itself which comes rated in Watts only. As a result, this usually leads to confusion as most people either lack the technical knowledge to understand the difference between VA and Watt units or, even worse, do not even realize that there is a difference.

When shopping for a UPS, almost everyone would have noticed that they are either rated in VA's only or in both VA's and Watt's. This is not so with the vast majority of household equipment, including the very power supply of the computer itself which comes rated in Watts only. As a result, this usually leads to confusion as most people either lack the technical knowledge to understand the difference between VA and Watt units or, even worse, do not even realize that there is a difference.

Of course, this is something natural because such knowledge is usually limited to electricians and electrical engineers, people who are educated and work on the AC power grid. To make matters worse, not only VAs (Volt-Amperes) and Watts are different but there is even a third "form of electrical power", Volt-Ampere reactive or VArs.

In this article, we will try and explain in terms comprehensible from the majority of users, who possess only basic skills and little to no knowledge on the matter, the difference between the three types of power.