There are approximately 40 countries that use 60 Hz while the rest typically run on 50 Hz current. Single-phase power is primarily for residential use (such as homeowners and what you would find in a hotel) while 3-phase electric power provides more stable, heavy-duty power for most industrial applications like manufacturing plants, commercial facilities, data centers, telecom towers, hospitals, food processing, and utility power plants.

Some applications use specialized higher voltages (such as 4160 V or 13,400 V) but these are on a more unique basis and typically involve transformers so those are not included. When considering a backup power generator, keep in mind that the frequency can often be changed by an accomplished power generation technician or electrical contractor but you do typically see a performance loss on most generator sets when you convert from 60 hertz to 50 hertz. This is mainly because you have to slow the engine RPM down and make adjustments so the overall kW or kVA output will be lower. The opposite is also true – you can sometimes gain kW when you convert from 50 Hz to 60 Hz because you speed the engine RPM up. The number of wires and plugs used varies greatly by region since each country is evolving their electrical grids at a different rate and over time so these are only provided as a good starting point and general guide.