What Is an Earthed Line Conductor (LE)? Definition, Examples, Requirements

Earthed line conductor (identification: LE): line conductor which has an electrical connection with a local earth (defined in the IEC TS 62257-5-2015).

The earthed line conductors are used in single-phase 2-wire AC electrical systems, in three-phase 3-wire AC electrical systems without the neutral and in 2-wire DC electrical systems.

Examples.

In single-phase TN-S (see Figure 31A4), TN-C-S (Figure 31B4) and TT (Figure 31F3) electrical systems without neutrals, there may be earthed line (phase) conductors.

TN-S system single-phase, 2-wire with separate the earthed line conductor and the protective conductor throughout the distribution system
Figure 31A4 [1] – TN-S system single-phase, 2-wire with separate the earthed line conductor and the protective conductor throughout the distribution system
TN-C-S system single-phase, 2-wire where the PEL conductor is separated into the protective conductor and the earthed phase conductor at the origin of the electrical installation
Figure 31B4 [1] – TN-C-S system single-phase, 2-wire where the PEL conductor is separated into the protective conductor and the earthed phase conductor at the origin of the electrical installation
TT system single-phase, 2-wire with the earthed phase conductor throughout the distribution system
Figure 31F3 [1] – TT system single-phase, 2-wire with the earthed phase conductor throughout the distribution system

Earthed phase conductors can also be in TN-S, TN-C-S and TT three-phase electrical systems whose power supplies have no neutrals. For example, Figure 31A2 shows a TN-S system in which the phase conductor LE3 is earthed. The three-phase TN-C-S and TT systems with earthed phase conductors LE3 are shown in figures 1 и 2.

TN-S system 3-phase, 3-wire with separate the earthed phase conductor and the protective conductor throughout the distribution system
Figure 31A2 [1] – TN-S system 3-phase, 3-wire with separate the earthed phase conductor and the protective conductor throughout the distribution system
TN-C-S three-phase three-wire system with separation of PEL conductor into an earthed line conductor and protective conductor at the input of the installation
Figure 1 – TN-C-S three-phase three-wire system with separation of PEL conductor into an earthed line conductor and protective conductor at the input of the installation (based on figure 6 from the book [2] by Y.V. Kharechko)
TT three-phase three-wire system
Figure 2 – TT three-phase three-wire system (based on figure 7 from the book [2] by Y.V. Kharechko)

Two-wire TN-S, TN-C-S, and TT DC electrical systems use earthed pole conductors that are connected to the earthed poles of the power supplies. Figures 31K, 31L, and 31H show examples of electrical systems in which the negative pole conductor L- is earthed.

TN-C-S DC 2-wire system
Figure 31K [1] – TN-C-S DC 2-wire system
TT DC two-wire system
Figure 31L [1] – TT DC 2-wire system
TN-S DC 2-wire system
Figure 31H [1] – TN-S DC 2-wire system

Color and alphanumeric identification requirements.

In the Russian Federation, the preferred colour of the earthed phase conductor is BLUE. If confusion with the neutral conductor, the mid conductor or the earthed pole conductor is likely, the alphanumeric designation shall be indicated at the terminations of the earthed phase conductors and in points of their connections. The alphanumeric identification of the earthed phase conductor of a single-phase electrical circuit shall be “LE”, and of a three-phase electrical circuit shall be “LE1 “, “LE2” or “LE3” [Annex B, 3].

In the Russian Federation, the preferred colour of the earthed pole conductor is BLUE. If confusion with the neutral conductor, the mid conductor or the earthed phase conductor is likely, the alphanumeric designation shall be indicated at the terminations of the earthed pole conductors and in points of their connections. The alphanumeric identification of the earthed positive pole conductor shall be “LE+”, the earthed negative pole conductor shall be “LE–” [Annex B, 3].

NOTE. Terms “phase conductor” and “pole conductor” are used for the identification of line conductors in AC systems and DC systems, respectively.

References

  1. IEC 60364-1
  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 60445-2021