What Is a Phase Conductor? Purpose, Definition & Meaning

Phase conductor: line conductor which is used in an AC electric circuit (defined in the IEC 60445:2021 [1]). In other words, it is a live conductor under normal conditions and is used to transmit electrical energy. In the United States and some other countries, the term “line conductor in AC system” is often used instead of the more correct term “phase conductor”.

Phase conductors together with neutral conductors are used in electrical installations of buildings to provide power for AC electrical equipment used in them.

Kharechko Y.V. in his book [2] supplements:

« Phase conductors are referred to as live parts. Under normal conditions, they are normally energized. The voltage of a phase conductor in relation to the neutral conductor or PEN conductor in single-phase and three-phase circuits is usually 230 V. The voltage between phase conductors in three-phase electrical circuits is usually 400 V. »

A phase conductor is a current-carrying conductor that is counted in the total number of electrical conductors used in an electrical circuit, network, or system.

Minimum cross-sectional areas of phase conductors are specified in IEC 60364-5-52, the same as those of line conductors (see table 52.2 in “Line Conductor (L)“). Phase conductors must be protected against overcurrent in the same way as line conductors.

Figure 1, for example, shows the phase conductors L1, L2, L3.

TN-C system with neutral and protective conductor functions combined in a single conductor throughout the system
Figure 31C [3] — TN-C system with neutral and protective conductor functions combined in a single conductor throughout the system

Designation and Marking

The alphanumeric identification of a phase conductor shall start with the letter “L” suffixed by [Clause 7.3.11, 1]:

  • a sequential number of phase conductors, starting with the digit one “1 “;

If no more than one phase conductor is used, the suffix may be omitted.

Phase conductors in AC systems shall be identified by the colours BLACK, BROWN or GREY. [Clause 6.2.3, 1].

Note 1. In the Russian Federation, the alphanumeric identification of the phase conductor of a single-phase electrical circuit shall be “L”. The alphanumeric identification of the phase conductors of a three-phase electrical circuit shall be “L1 “, “L2” and “L3”.

When the single-phase electrical circuit is branched from a three-phase electrical circuit, the alphanumeric identification of the phase conductor of the single-phase electrical circuit should coincide with the alphanumeric identification of that phase conductor of the three-phase electrical circuit to which it is connected electrically [Annex B, 1].

NOTE 2. In Australia, the colour BLACK shall not be used for identification of phase conductors of installation wiring. The colour BROWN is acceptable for a single-phase phase conductor and BROWN, BROWN and BROWN is acceptable for phase conductors L1, L2 and L3 [Annex B, 1].

NOTE 3. In Canada, where the colour GREY is used as a replacement for the colour identification BLUE for neutral or mid-point conductor, the colour GREY shall not be used for identification of phase conductors if confusion is likely [Annex B, 1].

NOTE 4. In the United States, where the colour GREY is used as a replacement for the colour identification BLUE for the neutral or mid-point conductor, the colour GREY shall not be used for identification of phase conductors if confusion is likely [Annex B, 1].

Color and alphanumeric marking of conductors for three-phase electrical installations of buildings

Note here that phasing is not implied by these colors (brown, black and gray). This means that you can, for example, mark the conductor L1 not only with brown insulation color, but also with gray or black.

Note 5. In the Russian Federation, the preferred colour of the phase conductor of a single-phase electrical circuit is BROWN.

When the single-phase electrical circuit is branched from a three-phase electrical circuit, the colour identification of the phase conductor of the single-phase electrical circuit should coincide with the colour identification of that phase conductor of the three-phase electrical circuit to which it is connected electrically [Annex B, 1].

color identification of conductors for single-phase electrical installations of buildings

References

  1. IEC 60445:2021
  2. Kharechko Y.V. Concise Terminological Dictionary of Low Voltage Electrical Installations. Part 1 // Appendix to the journal “Library of the safety engineer. – 2011. – № 3. – 160 c. Personal English translation by the author of this article.
  3. IEC 60364-1