Part of the Smart grid glossary:

Volt-ampere (VA) is a measurement of power in a direct current ( DC ) electrical circuit. The VA specification is also used in alternating current ( AC ) circuits, but it is less precise in this application, because it represents apparent power , which often differs from true power .

In a DC circuit, 1 VA is the equivalent of one watt (1 W). The power, P (in watts) in a DC circuit is equal to the product of the voltage V (in volt s) and the current I (in ampere s):

P = VI

In an AC circuit, power and VA mean the same thing only when there is no reactance . Reactance is introduced when a circuit contains an inductor or capacitor . Because most AC circuits contain reactance, the VA figure is greater than the actual dissipated or delivered power in watts. This can cause confusion in specifications for power supplies. For example, a supply might be rated at 600 VA. This does not mean it can deliver 600 watts, unless the equipment is reactance-free. In real life, the true wattage rating of a power supply is 1/2 to 2/3 of the VA rating.

When purchasing a power source such as an uninterruptible power supply ( UPS ) for use with electronic equipment (including computers, monitors, and other peripherals), be sure the VA specifications for the equipment are used when determining the minimum ratings for the power supply. The VA figure is nominally 1.67 times (167 percent of) the power consumption in watts. Alternatively, you can multiply the VA rating of the power supply by 0.6 (60 percent) to get a good idea of its power-delivering capability in watts.

Also see current , voltage , power , reactance , and watt .

This was last updated in March 2011
Contributor(s): Guillermo Cardenas
Posted by: Margaret Rouse

Related Terms

Definitions

  • thing (in the Internet of Things)

    - A thing, in the context of the Internet of things (IoT), is an entity or physical object that has a unique identifier, an embedded system and the ability to transfer data over a network. Given the ... (WhatIs.com)

  • full HDTV (ultra-HD, true HDTV, 1080p)

    - Full HDTV, also referred to as ultra-HD, true HDTV, and 1080p, is a television (TV) display technology that surpasses the video quality and sharpness of the original high-definition television (HDT... (WhatIs.com)

  • Internet of Things (IoT)

    - The Internet of Things (IoT) is a scenario in which objects, animals or people are assigned unique identifiers and given the ability to automatically transfer data over a network without requiring ... (WhatIs.com)

Glossaries

  • Smart grid

    - Terms related to smart grids, including definitions about utility electricity delivery systems and words and phrases about smart meters and distributing, monitoring and billing electrical power.

  • Internet applications

    - This WhatIs.com glossary contains terms related to Internet applications, including definitions about Software as a Service (SaaS) delivery models and words and phrases about web sites, e-commerce ...

Ask a Question. Find an Answer.Powered by ITKnowledgeExchange.com

Ask An IT Question

Get answers from your peers on your most technical challenges

Ask Question

Tech TalkComment

Share
Comments

    Results

    Contribute to the conversation

    All fields are required. Comments will appear at the bottom of the article.