Mains electricity is the general-purpose alternating-current (AC) electric power supply. In the US, electric power is referred to by several names including household power, household electricity, house current, powerline, domestic power, wall power, line power, AC power, city power, street power, and grid power. In many parts of Canada, it is called hydro, because much of the Canadian electrical generating capacity is hydroelectric.
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 their
Plugs and sockets (receptacles or outlets)
Earthing system (grounding)
Protection against overcurrent damage (e.g., due to short circuit), electric shock, and fire hazards
Single-phase or Three-phase electric power
All these parameters vary among regions. The voltages are generally in the range 100–240 V (always expressed as root-mean-square voltage). The two commonly used frequencies are 50 Hz and 60 Hz.
Foreign enclaves, such as large industrial plants or overseas military bases, may have a different standard voltage and frequency from the surrounding areas. Some city areas may use standards different from that of the surrounding countryside
Many other combinations of voltage and utility frequency, including direct current, were formerly used, with frequencies between 25 Hz and 133 Hz and voltages from 100 to 250 V. The modern standard combinations of 230 V/50 Hz and 120 V/60 Hz 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.
TABLE OF MAINS VOLTAGES AND OPERATING FREQUENCIES