What Is a Live Parts (in Electrical Installations and Equipment)?

Live parts: a conductive part intended to be energized under normal operating conditions, including the neutral conductor and mid-point conductor, but excluding the PEN conductor, PEM conductor and PEL conductor [defined in the IEC 60050-195-2021]. This term does not necessarily imply a risk of electric shock.

The term under consideration defines those conductive parts of electrical equipment and electrical installations which are energized during their operation under normal conditions. A live part, as a special case of a conductive part, has one distinguishing feature – it can be live under normal conditions. Conductive parts which are not energized under normal conditions, but which may become energized under fault conditions, are not live parts.

Examples of Live Parts

The live parts include phase and neutral conductors of AC electrical circuits, pole and mid conductors of DC electrical circuits, and other conductive parts of a low-voltage electrical installation that have electrical connections to these electrical conductors and are under normal conditions at an electrical potential different from the earth potential.

In Figure 1, the phase (L1, L2, L3) and neutral conductor N are shown as examples of live parts.

TN-C-S system 3-phase 4-wire where the PEN conductor is separated into the protective conductor and the neutral conductor at the origin of the electrical installation
Figure 1. TN-C-S system 3-phase 4-wire where the PEN conductor is separated into the protective conductor and the neutral conductor at the origin of the electrical installation

Why are PE, PEN, PEM, and PEL conductors not classified as live parts?

Protective conductors, including protective earthing conductor and protective equipotential bonding conductor, are not considered to be live parts, because under normal conditions they are at an electrical potential almost equal to the earth potential.

The PEN conductor is not considered to be a live part, even though this conductor performs the function of a neutral conductor.

The PEM conductor is also not considered to be an live part, although this conductor performs the function of a mid-point conductor.

The PEL conductor is not considered a live part, even though the line conductor, of which it serves, is the most characteristic example of a live part.

Because the electrical potential of the electrically live parts of the electrical installation of a building is different from that of the earth, which is nearly zero, and the conductive parts connected to the earth, they must be reliably insulated.

Any human or animal contact with an live part that has a voltage greater than the extra-low voltage can result in an electric shock. Such live parts pose a particular hazard to humans. They are referred to in regulatory and legal documentation as hazardous-live-parts.

References

  1. IEC 60050-195-2021
  2. IEC 60364-1