<P> A volt - ampere (VA) is the unit used for the apparent power in an electrical circuit, equal to the product of root - mean - square (RMS) voltage and RMS current . In direct current (DC) circuits, this product is equal to the real power (active power) in watts . Volt - amperes are useful only in the context of alternating current (AC) circuits (sinusoidal voltages and currents of the same frequency). </P> <P> Some devices, including uninterruptible power supplies (UPSs), have ratings both for maximum volt - amperes and maximum watts . The VA rating is limited by the maximum permissible current, and the watt rating by the power - handling capacity of the device . When a UPS powers equipment which presents a reactive load with a low power factor, neither limit may safely be exceeded . For example, a (large) UPS system rated to deliver 400,000 volt - amperes at 220 volts can deliver a current of 1818 amperes . </P> <P> VA ratings are also often used for transformers; maximum output current is then VA rating divided by nominal output voltage . Transformers with the same sized core usually have the same VA rating . </P> <P> The convention of using the volt - ampere to distinguish apparent power from real power is allowed by the SI standard . SI allows one to specify units to indicate common - sense physical considerations . </P>

What is the difference between amps and volt amps