Why are different household AC electrical service voltages and frequencies used in the various countries around the world?

Answer 1

Single-phase voltage and frequency

Countries in Europe and in many other areas of the world use a standard mains supply voltage for households and businesses of between 220 and 240 volts for lighting as well as for high-powered appliances. This is twice that of the voltage used for ordinary lighting and low-power appliances in US, Canada and most of the Americas, and also Japan. In those countries, and others using the same power distribution system, the standard mains supply voltage for low-power appliances is between 115 and 127 volts.

Note that currently all new American buildings in fact get 240 volts split into two 120 volts "hot" wires (often called "legs") with a common neutral wire. Major appliances, such as virtually all drying machines and ovens, are now connected to 240 volts.

The mains frequency in Europe and other 230 Volt areas is 50 Hz (Cycles per second) compared to 60 Hz in US, Canada and other 120/240 Volt areas. Some 60 Hz appliances will work fine but others with simple motors will run too slow on the lower frequency of 50 Hz. Similarly, some 50 Hz appliances will work fine but others with simple motors will run too fast on the higher frequency of 60 Hz.

However the most important difference is how the Neutral wire is connected:

240 volt 50 Hz service

A 240 volt 50 Hz appliance can have up to 3 wires altogether:

• one single 240 volt "live" or "hot" wire;
• a neutral wire;
• a safety "earth" or "ground" wire but this is not required if the appliance is of the type known as "double insulated".

The hot wire feeds alternating voltage from the power station to the load and, because the voltage is alternating, the load draws an alternating current. Then the neutral wire returns the current to the power station to complete the circuit.

240 volts 60 Hz service

An appliance that is designed to be connected to strictly 240 volts 60 Hz is connected with only a two wire cable plus a safety ground wire. (For example 240 volt 60 Hz base board heaters use that.)

The only time a cable with three wires plus safety ground is used is if 120/240 volts is needed in the equipment. (For example kitchen ranges or washing machines which have time clocks or programmers that require only a 120 volt feed.)

Thus an appliance designed to run on a 240/120 volt 60 Hz supply can have up to 4 wires altogether:

• two 120 volt 60 Hz live "hot legs" which run in opposing phase to one another: when one hot leg goes "+" (120 volts positive) the other leg goes "-" (120 volts negative);
• a neutral wired as a "central" common current return conductor:
• a safety "ground" wire but this is not required if the appliance is of the type known as "double insulated".

One of the two hot wires feeds a 120 volt alternating voltage from the power station to the 120 volt load - the clock or programmer - and, because the voltage is alternating, that load draws an alternating current. Then the neutral wire returns the current to the power station to complete the circuit.

Important conclusion

There is a 240 volt voltage difference between the neutral and the hot conductor in the 50 Hz system and only a 120 volt voltage difference between the neutral and each of the hot conductors in the 60 Hz system.

That is why an appliance designed to be connected onto the 50 Hz system cannot be used safely on the 60 Hz system without first having a proper technical inspection done, followed by any necessary modification work done to ensure that the appliance can be operated safely because, in the main breaker box, at the point where the 60 Hz "neutral" gets connected to the ground, this difference will cause serious problems!

A licensed electrician or electrical engineer would be able to consider whether or not a particular large appliance, that was manufactured to work on 50 Hz-only, could be modified to run safely at the higher 60 Hz frequency. However it won't usually be worth the expense of doing the work because it would be more cost-effective to buy (new or secondhand) an equivalent large appliance designed to work on 60 Hz.

The system of three-phase alternating current electrical generation and distribution was invented by a nineteenth century creative genius named Nicola Tesla. He made many careful calculations and measurements and found out that 60 Hz (Hertz, cycles per second) was the best frequency for alternating current (AC) power generating. He preferred 240 volts, which put him at odds with Thomas Edison, whose direct current (DC) systems were 110 volts. Perhaps Edison had a useful point in the safety factor of the lower voltage, but DC couldn't provide the power to a distance that AC could.

When the German company AEG built the first European generating facility, its engineers decided to fix the frequency at 50 Hz, because the number 60 didn't fit the metric standard unit sequence (1,2,5). At that time, AEG had a virtual monopoly and their standard spread to the rest of the continent. In Britain, differing frequencies proliferated, and only after World War II was the 50-cycle standard established.

However that might have been a mistake! Not only is 50 Hz 20% less effective in generation, it is 10 - 15% less efficient in transmission and requires up to 30% larger windings and magnetic core materials in transformer construction. Electric motors are much less efficient at the lower frequency, and must also be made more robust to handle the electrical losses and the extra heat generated. Today, only a handful of countries (Antigua, Guyana, Peru, the Philippines, South Korea and the Leeward Islands) follow Tesla's advice and use the 60 Hz frequency together with a voltage of 220 - 240 V.

Originally Europe was 120 V too, just like Japan and the US today. It has been deemed necessary to increase voltage to get more power with less losses and voltage drop from the same copper wire diameter. At the time the US also wanted to change but because of the cost involved to replace all electric appliances, they decided not to. At the time (1950s-1960s) the average US household already had a fridge, a washing-machine, etc., but not in Europe.

The end result is that now it may seem, to some people, that the US has not evolved from the 1950s and 1960s, and still copes with problems as light bulbs that burn out rather quickly when they are close to the transformer (too high a voltage), or just the other way round: not enough voltage at the end of the line. (115 to 127 volt spread!).

For more information see the answers to the Related Questions shown below.

If you are interested to know what what the different standard mains voltages and frequencies are around the world - and what the various plugs look like - the Related Link shown below has all the details.