The magnitude of the household voltage or frequency is not the same in the US (United States) and Europe. This is mostly because of three reasons:
1- Due to the competition between the United States and Europe in the late 1800s and early 1900s, manufacturing companies in both continents independently developed their power system equipment without coordinating their efforts.
2- Different safety concerns in Europe and the United States have led to various voltage standards.
3- Wiring and equipment costs have led nations to select the most economical voltage standards.
In the United States, 120 V is used everywhere inside the house, except for heaters, dryers, and ovens where the receptacles are double-pole at 240 V. On the other hand, Europe uses 230 V inside the house but 400 V in high-power appliances.
The table below shows the voltage and frequency standards in select countries:
The various voltage and frequency standards in Europe and US have created confusion among consumers who wish to use equipment manufactured based on one standard in a country with a different standard. For example, the compressors of the refrigerators designed for 60 Hz standard can slow down by 17% when used in a 50 Hz system. Also, electrical equipment designed for 120 V standards will be damaged if it is used in 230 V systems. For small appliances, modern power electronics circuits have addressed this problem very effectively. Almost all power supplies for travel equipment (electric razors, portable computers, digital cameras, audio equipment, etc) are designed to operate at all voltage and frequency standards.
It appears that the 120 V was chosen somewhat arbitrarily in the United States. Thomas Edison came up with a high-resistance lamp filament that operated well at 120 V. Since then, the 120 V was selected in the United States. The standard for voltage in Europe is 230 V. Generally, a wire is less expensive when the voltage is high; the cross-section of the copper wires is smaller for higher voltages. However, from the safety point of view, lower voltage circuits are safer than higher voltage ones; 120 V is perceived to be less harmful than 230 V.
Only two frequencies are used worldwide: 60 and 50 Hz. The standard frequency in North America, Central America, most of South America, and some Asian countries is 60 Hz. Almost everywhere else, the frequency is 50 Hz. In Europe, major manufacturing firms such as Siemens and AEG have established 50 Hz as a standard frequency for their power grids. In the United States, Westinghouse adopted the 60 Hz standard. Nikola Tesla actually wanted to adopt a higher frequency to reduce the size of the rotating machines, but 60 Hz was eventually selected for the following reasons:
- It is a high enough frequency to eliminate light flickers in certain types of incandescent lamps.
- It is conveniently synchronized with time.
Machines designed for 60 Hz can have less iron and smaller magnetic circuits than the ones designed for 50 Hz. It is interesting to know that for stand-alone systems, such as aircraft power systems, the frequency is 400 Hz. This is selected to reduce the size and weight of the rotating machines and transformers aboard the aircraft.