Editing Mains electricity (section)

== Power systems ==
{{For|a list of voltages, frequencies, and wall plugs by country|Mains electricity by country}}

Worldwide, many different mains power systems are found for the operation of household and light commercial electrical appliances and lighting. The different systems are primarily characterized by:
* [[Voltage]]
* [[Utility frequency|Frequency]]
* [[AC power plugs and sockets|Plugs and sockets]] (receptacles or outlets)
* [[Earthing system]] (grounding)
* Protection against [[overcurrent]] damage (e.g., due to short circuit), [[Electrical injury|electric shock]], and fire hazards
* Parameter tolerances.

All these parameters vary among regions. The voltages are generally in the range 100–240&nbsp;[[Volt|V]] (always expressed as [[root-mean-square]] voltage). The two commonly used frequencies are 50&nbsp;[[Hertz|Hz]] and 60&nbsp;Hz. [[Single-phase electric power|Single-phase]] or [[Three-phase electric power|three-phase]] power is most commonly used today, although two-phase systems were used early in the 20th century. Foreign enclaves, such as large industrial plants or overseas military bases, may have a different standard voltage or frequency from the surrounding areas. Some city areas may use standards different from that of the surrounding countryside (e.g. in [[Libya]]). Regions in an effective state of [[anarchy]] may have no central electrical authority, with electric power provided by incompatible private sources.

Many other combinations of voltage and utility frequency were formerly used, with frequencies between 25&nbsp;Hz and 133&nbsp;Hz and voltages from 100&nbsp;V to 250&nbsp;V. [[Direct current]] (DC) has been displaced by alternating current (AC) in public power systems, but DC was used especially in some city areas to the end of the 20th century. The modern combinations of 230&nbsp;V/50&nbsp;Hz and 120&nbsp;V/60&nbsp;Hz, listed in [[IEC 60038]], did not apply in the first few decades of the 20th century and are still not universal. Industrial plants with three-phase power will have different, higher voltages installed for large equipment (and different sockets and plugs), but the common voltages listed here would still be found for lighting and portable equipment.