Which terms are AC voltages normally specified in?

AC voltages are normally specified in RMS (Root Mean Square) values because RMS provides a useful way to express the effective value of an alternating current (AC) waveform. The RMS value is equivalent to a direct current (DC) value that would deliver the same amount of power to a load.

In practical applications, such as household power, appliances, and electronic devices, the RMS voltage gives a clear indication of the voltage level that will be experienced or utilized by the devices. For example, when an AC voltage is listed as 120 volts, this refers to the RMS value. It allows for easier power calculations and comparisons between different types of electrical systems.

While peak values, average values, and instantaneous values provide different information about the AC waveform, they do not represent the effective voltage as accurately as the RMS value does in the context of power delivery and usage. Peak values, for instance, might indicate the maximum voltage but do not relate to the consistent power realized by most devices. Average values are often less than RMS values for AC signals, and instantaneous values fluctuate continuously at any given point in time, which does not provide a standard measure for practical use.