Key to Terms Used in This Publication

Type of Current - a.c. indicated alternating current and d.c., direct current

Frequency - Shown in number of hertz (cycles per second). Even if voltages are similar, a 60-hertz U.S. clock or tape recorder will not function properly on 50 hertz current.

Number of phases - 1 and 3 are the conventional phases which may be available.

Nominal voltages - Direct current nominal voltages, for example are: 110/220 and 120/240. The lower voltage is always 1/2 of the higher voltage. On a direct current installation, the lower voltage requires two wires while the higher voltage requires three wires.

Alternating current nominal voltage: Alternating current is normally distributed either through 3 phase wye ("star") or delta ("triangle"), 4-wire secondary distribution systems. In the wye or star distribution system the nominal voltage examples are: 120/208, 127/220, 220/380, and 230/400. The higher voltage is 1.732 (the square root of 3) times the lower voltage. In a delta or triangle system, 110/220 and 230/460 are examples of nominal voltages. The higher voltage is always double the lower voltage.

The higher voltage is obtained by using 2 or 3 phase wires and the neutral wire while the lower voltage is the voltage between the neutral wire and one phase wire. The higher voltage may be single or 3 phase while the lower voltage is always single phase and used primarily for lighting and for small appliances.

In this report the term nominal voltage is used to denote the reported voltage in use in the majority of residential and commercial establishments in the city or area named.

Type of attachment plug in use - Attachment plugs used throughout the world come in various forms, dimensions and configurations too numerous to describe in this report. This report does, however, attempt to point out the basic and most commonly used types of plugs by the country. Adapters may be purchased to change from the American type to other types.

Number of wires to the consumer - The number of wires which may be used by the consumer is shown. Normally, a single phase, 220/380 volt system or 127/220 system will have two wires if only the lower voltage is available (one phase wire and the neutral). It will have three wires if both the higher and lower voltages are available (two phase wires and the neutral) and where three phase motors will be used, four wires will be available for the higher voltage (three phase wires and the neutral wire).

Frequency stability - A "yes" in the column indicated that the frequency stability is stable and that service interruptions are rare.

Footnotes: Footnotes denote specific country published variances.