What do voltmeters read when measuring voltage?

Voltmeters are designed to measure the effective voltage of an AC (alternating current) waveform, which is often referred to as root mean square (RMS) voltage. This value is crucial because it represents the equivalent direct current (DC) voltage that would produce the same amount of heat in a resistor as the AC voltage does.

When measuring voltage, especially in residential and commercial power systems, the effective voltage gives a more practical understanding of the energy delivered by the AC signal. It allows linemen and electricians to determine the actual working voltage available for appliances and devices, ensuring safe and efficient operation.

The other forms of voltage measurements, such as peak voltage, average voltage, and instantaneous voltage, do not provide the same practical and reliable measurement for the purposes of electrical installation and maintenance. For example, peak voltage represents the highest value of voltage in a waveform but does not account for the overall power delivery capability. Average voltage can be misleading since it is affected by the waveform shape and may not convey meaningful information in systems with sinusoidal waveforms. Instantaneous voltage measures the voltage at a specific moment in time, which is not practical for assessing overall system performance.