Watts vs. VA: What’s the difference anyway?

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Between the increasingly fragile power grid, the escalating power consumption of IT equipment and the constantly increasing importance of our network, it isn’t difficult to see the value a UPS (uninterruptible power supply) has to not only a business but a home. So have you ever decided to research some UPSs to see which is the right fit for you, only to be left asking yourself, “Watts? VA? Huh?”

Most of us have heard of watts before – and have some understanding that each piece of equipment has a certain amount of watts it draws to operate, but how exactly does that relate to a UPS? And what does VA stand for anyway?

What are watts?

Watts is the standard unit for measuring power, which defines how quickly energy is used or transferred. In electrical systems, watts tell us how much energy an appliance or device consumes per second. For example, a 100-watt light bulb uses more energy per second than a 60-watt bulb, meaning it’s brighter. Watts is also used to measure the output of other energy-consuming devices.

What does VA stand for?

Electronics have both maximum watt ratings and maximum VA (volt-ampere) ratings; and neither the watt nor the VA rating of a UPS may be exceeded by the attached equipment (load). Watts is the real power drawn by the equipment, while volt-amps are called the “apparent power” and are the product of the voltage applied to the equipment times the current drawn by the equipment. The watt rating determines the actual power purchased from the utility company and the heat loading generated by the equipment; and the VA rating is used for sizing wiring and circuit breakers.

Any clearer? Probably not much.

Working principle of watts and VA (volt-ampere)

The distinction between VA vs watts is essential for sizing electrical equipment like UPSs, ensuring they can handle the full power demand and not just the ‘real power’ used by devices.

What you really need to know is that for electronics such as computers and UPSs, watt and VA ratings can differ significantly; with the VA rating always being equal to or larger than the watt rating. The ratio of the watts to VA is called the “Power Factor” and is expressed either as a number (i.e. – 0.8) or a percentage (i.e. 80%). This power factor is what really matters when sizing a UPS for your specific requirements.

APC™ by Schneider Electric’s™ latest generation of Smart-UPS™ On-Line now delivers innovative features to help you make the most of your energy™. Models 6kVA (6000 VA) and higher have a unity power factor – which means VA translates to an equal amount of watts (i.e. 6000 VA = 6000 Watts). Smaller models of the next generation of Smart-UPS On-Line have a 0.9 power factor or higher, and all are Energy Star™ qualified regardless of VA.

The difference between 0.8 or 0.9 power factors and a unity power factor (1.0) may not sound like much – but when you take into account the fact that the extra available wattage can be used to support additional loads and extend runtimes; it is easy to see how the next generation of Smart-UPS On-Line will increase your availability while saving you money.

Please refer to our UPS Selector for help properly sizing a UPS. Alternatively, if you are looking to upgrade your current UPS, refer to our UPS Upgrade Selector; and don’t forget to utilize our Trade-UPS Program which allows you to receive up to a 25% discount on the purchase of a new APC by Schneider Electric UPS when you trade in your old model, regardless of the manufacturer.

For further discussion regarding the differences between watts and VA please refer to White Paper 15, Watts and Volt Amps: Powerful Confusion.

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