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Definition of voltage ranges

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As per IEC voltage standards and recommendations:

Three-phase four-wire or three-wire systems Nominal voltage (V)

Single-phase three-wire systems Nominal voltage (V)

50 Hz 60 Hz 60 Hz
- 120/208 120/240(d)
230 240(c) -
230/400(a) 230/400(c) -
  277/480(a)  
  480  
  347/600  
  600  
400/690(b)   -
1000 600 -

(a) The value of 230/400 V is the result of the evolution of 220/380 V and 240/415 V systems which has been completed in Europe and many other countries. However, 220/380 V and 240/415 V systems still exist.
(b) The value of 400/690 V is the result of the evolution of 380/660 V systems which has been completed in Europe and many other countries. However, 380/660 V systems still exist.
(c) The value of 200 V or 220 V is also used in some countries.
(d) The values of 100/200 V are also used in some countries on 50 Hz or 60 Hz systems.


Fig. A1: Standard voltages between 100 V and 1000 V (IEC 60038 Edition 7.0 2009-06)


Series I Series II
Highest voltage for equipment (kV) Nominal system voltage (kV) Highest voltage for equipment (kV) Nominal system voltage (kV)
3.6(b) 3.3(b) 3(b) 4.40(b) 4.16(b)
7.2(b) 6.6(b) 6(b) - -
12 11 10 - -
- - - 13.2(c) 12.47(c)
- - - 13.97(c) 13.2(c)
- - - 14.52(b) 13.8(b)
(17.5) - (15) - -
24 22 20 - -
- - - 26.4(c, e) 24.94(c, e)
36(d) 33(d) 30(d) - -
- - - 36.5(2) 34.5(c)
40.5(d) - 35(d) - -

Note 1: It is recommended that in any one country the ratio between two adjacent nominal voltages should be not less than two.

Note 2: In a normal system of Series I, the highest voltage and the lowest voltage do not differ by more than approximately ±10 % from the nominal voltage of the system. In a normal system of Series II, the highest voltage does not differ by more then +5 % and the lowest voltage by more than -10 % from the nominal voltage of the system.
(a) These systems are generally three-wire systems, unless otherwise indicated. The values indicated are voltages between phases.
The values indicated in parentheses should be considered as non-preferred values. It is recommended that these values should not be used for new systems to be constructed in future.
(b) These values should not be used for new public distribution systems.
(c) These systems are generally four-wire systems and the values indicated are voltages between phases. The voltage to neutral is equal to the indicated value divided by 1.73.
(d) The unification of these values is under consideration.
(e) The values of 22.9 kV for nominal voltage and 24.2 kV or 25.8 kV for highest voltage for equipment are also used in some countries.


Fig. A2: 'AC 3 phases Standard voltages above 1 kV and not exceeding 35 kV (IEC 60038 Edition 7.0 2009)(a)