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Transformer converters are designed to power household and industrial appliances with 220VAC or 110VAC. They are specially designed for electronic equipment whose nominal AC voltage is different from the local electrical network. Converters are extremely useful for appliances which are bought in the US, but consumers want to use them in Bulgaria or other European countries. Vice versa is also possible, because each converter is bi-directional, i.e. devices with 230VAC standard voltage will have to be connected after a converter in order to be used in countries with rated voltage of 110 VAC. Some areas use standards other than those of the country to which they belong (e.g. Hong Kong in China).

Areas, such as large industrial zones or military bases, may have different standard voltage and frequency compared to their surroundings. Even some urban areas could use electrical network with standard parameters other than those, which are typical for the country in which they are located. Regions with anarchic government may not have united power distribution unit but separate networks with incompatible parameters. Countries with more than one standard voltage for household consumers are (in alphabetical order):

Algeria (220 / 127V), Antigua and Barbuda (240 / 120V), Azerbaijan (208 / 120V, but also 240 / 120V), Barbados (230 / 115V), Belarus (220 / 127V), Brazil (220 / 127V), Canada (127 / 240V), Colombia (120 / 240V), Kazakhstan (220 / 127V), Kyrgyzstan (220 / 127V), Libya (230 / 127V), Madagascar (220 / 110V), Mali (220 / 110V), Mexico (127 / 220V), Moldova (220 / 127V), Saudi Arabia (220 / 110V), Senegal (220 / 110V), Syria (220 / 115V), USA: Charlotte (North Carolina); Detroit (Michigan); Miami (Florida) (120 / 208V), New York, Pittsburgh, Los Angeles, Portland, San Francisco, Toledo (120 / 240V) Tajikistan (220 / 127V), Philippines (110/220), Jamaica (220 / 110V), Japan East (200 / 100V). The first figure shows the more common voltage. Very often the second common voltage is used in separate semi-autonomous areas, individual cities or in closed military areas or islands.

All European and most Asian countries use power that is within 220-230 V, while Japan, South Korea, Martinique, North America and parts of South America usе voltage between 100 and 127 V. In Yemen the used voltage is 250V, which goes beyond the standard allowance. Based on the harmonization of voltage in all countries of the European Union, the network has nominal voltage of 230 V ± 10% at a frequency of 50 Hz. During the transitional period 1995 – 2008 countries that had previously used 220 V began to use asymmetric narrow tolerance range of 230 V +6% -10% and those (such as Britain) which previously used 240 V started using 230 V +10% -6%.

It should be noted that it is not necessary to change the voltage in systems with a rated voltage of 220 V and 240 V, as they fall within the acceptable range 230 V ± 6%. In practice, this means that countries such as Britain, which previously used 240 V, continue to work with this voltage, as well as those which used 220 V. However, appliances must be designed to operate at voltages within the whole specified range. Historically, in the late 19th century, Westinghouse decided to use a frequency of 60 Hz for the USA, and AEG in Germany – 50 Hz, so in the end, the world was divided into two camps with different frequency. Most systems operating at 60 Hz have voltage of 120 V, and most networks at 50 Hz have 230 V.

In the United States and Canada national standards indicated that the nominal voltage of the source must be 120 V, this allows tolerance in the range of 114 to 126 V (± 5%). Historically, 110, 115 and 117 V were used at different times and different places in North America. Sometimes the network is said to be “110” although its nominal voltage is 120 V.
In 2000 Australia moved to standard voltage 230 V with a tolerance + 10% – 6%, replacing the old standard of 240 V, AS2926-1987. In the UK, 240 V remains within the limits of the new standard and networks continue to be called “two hundred and forty.”
In Japan, power supply to households is at 100 V. Eastern and northern parts of Honshu (including Tokyo) and Hokkaido have a frequency of 50 Hz, while western Honshu (including Nagoya, Osaka and Hiroshima), Shikoku, and Okinawa and Kyushu work at 60 Hz. To bridge the gap, most of the appliances can be switched into operation of the respective frequency.

The use of converters is necessary because of the different standards in the different countries. In the US, the frequency is 60 Hz, and the voltage is 110 VAC, but there are cities where the voltage is 120V. As for the main portable electronic devices – laptops or tablets, modern adapters usually have all-purpose inputs which indicate the unit can be supplied with voltage in the range of 100-230V. However, if the adapter is not of this type, a converter is required.

From everything listed above, it is clear that a significant part of the world has operating voltage and frequencies other than the standard ones in Bulgaria. In today’s world traveling to distant and exotic destinations is becoming more easy and frequent, so a converter in the luggage is imperative, even if you need it only for a coffee maker or a curling iron.

Converters, the main part of which is the transformer, are chosen according to their power, which applies to the transformer as well. We will also note that many countries have different standards for contact systems, other than Schuko, as is the standard in Bulgaria. For example, the grounding in France happens through a pin, which is placed in the socket outlet symmetrically to the sockets for phase and neutral, with which it forms an equilateral triangle. In Italy there are three round pins arranged in a row in the plug and accordingly three holes in the socket outlet. In England the pins are flat plates, etc.

1.Izrael 2. South Africa 3.Italia, Ethiopia, Chile

For this purpose converters have openings, allowing different standards to be connected, and when this is not possible, it is better to buy the right adapter. But let’s look at the power. It is written on the converter and indicates the maximum active power. When consumers with inductive or capacitive power are connected, it is necessary to provide a reserve of 3 to 5 times in relation to the active power. In other words, if you connect a drill or air conditioning after the converter and they have load of 300W, 300×5 = 1500W, and you need to select a converter with 1,5kW power.


Other essential condition for the proper and safe operation of the converter is to plug both terminals correctly. You have to be careful not to plug the terminal which has indication 110V to the 220V socket, because it will burn. I know it sounds simple, but this is one of the most common accidents with converters.


Usually there is also a power cable in the kit, at one end of which there is a bipolar plug with round pins and at the other end – the same plug but with flat pins.
Depending on the low-voltage electrical network to which you will connect the converter, you need to use the corresponding terminal of the power cable because, as mentioned above, a converter is a bidirectional device. In some cases the cable is connected to the device and then the converter looks like an adapter.

Another advantage of each transformer converter is that it separates galvanically the electrical circuit and thus it protects the devices, which are plugged-in after it, from short circuits in the network. However, if the consumer that is plugged-in after the converter needs grounding, this should be done additionally, because there is a bipolar connection.
DC converters, which convert 24V direct voltage to 12V direct voltage, or vice versa, are also quite common. But let’s make this a topic of another article.


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