What is the difference between watts and volt-amperes?

You’ll notice that specs for uninterruptible power systems seldom if ever mention watts (W), but instead speak in terms of volt-amperes (VA). Watts refer to “real power,” while volt-amperes refer to “apparent power.” Both are simply the product of voltage (V) multiplied by amperage (A). Thus, a device drawing 3 amps at 120 volts would be rated at 360 watts or 360 volt-amperes.

So what’s the difference, then?

The resistance in a DC circuit is pure resistance, which is limited to the impedance (measured in ohms) of the conductor(s). Thus, watts are a good measure of “real power,” and if you have three 120 VDC devices calculated to work at 200 watts, 400 watts, and 600 watts respectively, then you can just add them linearly to know how much power the circuit requires, which would be 1200 watts (1.2 KW).

In contrast, AC circuits also have inductive resistance, mostly caused by the build-up and collapse of the current with every 60 Hz excursion of the sinusoidal wave. This means that depending on their respective amperage requirements, three 120 VAC servers rated at 200 VA, 400 VA, and 600 VA respectively will not necessarily add up to 1200 VA (1.2 KVA). In sum, “volt amps” is a warning to proceed with caution.

So what to do?

Calculating the required current capacities for datacenters and other power-dense applications is both an art and a science that depends mightily on professional knowledge and experience. Depend on N1 Critical Technologies to make sure you have enough capacity not only for today—but also to meet your future growth requirements.

We leverage our practical experience designing high-quality power backup systems and other emergency uninterruptible power supply systems with our intimate knowledge of the specifications, capabilities, and service histories of the entire range of UPS products and systems available to you.

We can show you how to meet or exceed the technical parameters desired by your IT professionals in the most cost-effective manner, using the UPS products and systems that will provide the most robust uninterruptible power supply solution at the optimal price point.

Email today to arrange a no-cost assessment of your needs, or phone 877-226-3311.

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