Translations:Electricity types/7/en
In alternating current (AC) circuits the voltage goes through a cycle as positive and negative change many times each second, which causes the current to change its direction of flow. The voltage of an AC circuit can be represented as a wave on a graph (the graphic at right depicts on full AC cycle). It is important to note that when measuring the voltage of AC circuits with a multimeter the reading will always appear positive because it is calculated using a method called root mean square that results in negative values being treated as positive values in order to be able to create a comparison to DC. The brief negative cycles are included into this calculation. The voltage during one of these cycles can be graphically depicted as a sine wave for off-grid PVs systems that have a pure sine wave inverter.
The grid is almost entirely built to function with alternating current, although the voltage, frequency and number of wires in a supply circuit varies around the world. Nearly all electronic devices - cell phones, radios, computers and televisions - run on DC internally, but they incorporate electronics to convert from AC to DC in order to function with the grid. Appliances with motors or compressors - refrigerators, fans, and tools - have motors that can run directly on alternating current. Most countries use different voltages for different service types (residential, commercial, industrial). Some countries also have voltages and frequencies that vary based upon location as the grid has not been standardized. The wiring configuration - two-wire single phase (L1, N), three-wire single phase (L1, L2, N), three phase (L1, L2, L3) - can vary for the same voltage from country-to-country as well. Three phase services are typically used for commercial and industrial applications as they run motors more smoothly and can supply more current at the same voltage compared to non-three phase services. See Special:MyLanguage/Voltage and frequency by country for the voltage and frequency for specific countries.
