What Is a PEN Conductor?

PEN conductor: conductor combining the functions of both a protective earthing conductor and a neutral conductor (defined in the IEC 60050-195).

A PEN conductor, like other protective conductors, is not classified as a live part. However, a PEN conductor is a current-carrying conductor that is included in the total number of conductors used in an electrical circuit, network or system.

The requirements in IEC 60364-4-41:2005 clause 411.4.2 for TN systems require that the neutral point be earthed. The PEN conductor can be connected to the earthed neutral point of a multi-phase power supply or to the midpoint of a single-phase power supply.

That is, in low-voltage AC electrical installations or parts thereof, the functions of a protective earth conductor and a neutral conductor can be combined in one conductor. This conductor is referred to as a combined protective earth conductor and neutral conductor. However, it is better known by its short name “PEN conductor” or simply “PEN”.

Examples of Systems with PEN Conductors

In TN-C and TN-C-S single-phase electrical systems, which have power supplies with midpoints (neutrals), PEN conductors may be present. Figure 1 shows a single-phase two-wire TN-C system in which PEN conductors are used in both the electrical distribution network and the low-voltage electrical installation connected to it.

TN-C single-phase two-wire system
Figure 1. TN-C single-phase two-wire system

While in the TN-C-S system the PEN conductors are separated into protective and neutral conductors at the origin of the low-voltage electrical installation, as shown in Figure 2, the PEN conductors can only be in the electrical distribution network.

Figure 31B3 – TN-C-S system single-phase, 2-wire where the PEN conductor is separated
Figure 2. TN-C-S system single-phase, 2-wire where the PEN conductor is separated into the protective conductor and the neutral conductor at the origin of the electrical installation (based on figure 31B3 from IEC 60364-1)

NOTE 1. Neutral and protective conductor functions combined in a single conductor in a part of the distribution system.
NOTE 2. Additional earthing of the PEN conductor in the distribution line and of the protective conductor in the electrical installation may be provided.

If PEN conductors are separated elsewhere in the electrical installation, PEN conductors are used in the head part of the installation, and protective and neutral conductors are used in other parts of the electrical installation (see Figure 3).

TN-C-S single-phase two-wire system
Figure 3. TN-C-S system single-phase, 2-wire where the PEN conductor is separated into the protective conductor PE and the neutral conductor N elsewhere in the electrical installation

PEN conductors are also common in TN-C (Figure 4) and TN-C-S (Figures 5 and 6) three-phase electrical systems whose power supplies have neutrals.

TN-C system 3-phase, 4-wire with neutral and protective conductor functions combined in a single conductor throughout the distribution system
Figure 4. TN-C system 3-phase, 4-wire with neutral and protective conductor functions combined in a single conductor throughout the distribution system (based on Figure 31C of IEC 60364-1)
TN-C-S system 3-phase, 4-wire where the PEN conductor is separated into the protective conductor and the neutral conductor elsewhere in the electrical installation
Figure 31B1 – TN-C-S system 3-phase, 4-wire where the PEN conductor is separated into the protective conductor and the neutral conductor elsewhere in the electrical installation
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 6. 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 (based on figure 31B2 of IEC 60364-1)

PEN Conductor Requirements

  • The requirements of some IEC 60364 standards prohibit the use of PEN conductors in certain low-voltage electrical installations or parts thereof. For example, in order to reduce electrical and electromagnetic effects on electrical equipment, clause 444.4.3 of IEC 60364-4-44:2007 prohibits the use of PEN conductors in newly created electrical installations of buildings in which information equipment will be installed. The PEN conductor of an electrical distribution network must be separated into a protective conductor and a neutral conductor at the origin of of the electrical installation of building.
  • In existing electrical installations of buildings, it is recommended to replace PEN conductors with protective and neutral conductors. That is, electrical installations of buildings with information equipment must comply with the TN-S type of system earthing. If the TN-C-S system is used, the PEN conductor must be separated into a protective conductor and a neutral conductor at the origin the electrical installation of the building.
  • For a TN-system, the final circuit for the supply to a leisure accommodation vehicle, tent or residential park home shall not include a PEN conductor [clause 708.312.2.1 of IEC 60364-7-708-2017].
  • For a TN-system, the final circuits for the supply of pleasure craft or houseboats shall not include a PEN conductor [clause 709.312.2.1 of IEC 60364-7-709-2012].
  • The requirements of clause 710.312.2 of IEC 60364-7-710, poorly worded, do not permit the use of the TN-C system in the electrical installations of medical facilities after the main switchboard. That is, they also prohibit the use of PEN conductors in these electrical installations.

Requirements for PEN conductors are also published in IEC 60364-5-54. Since a PEN conductor has the functions of protection against electric shock performed by a protective earthing conductor, it must first comply with the requirements for a protective conductor.

Above all, the continuity of the electrical circuit of the PEN conductor must be ensured. Switching devices such as fuses, circuit breakers, residual current devices, etc. must therefore not be included in its circuit. Separate terminals or busbars for connecting protective and neutral conductors must be installed at the point of separation of the PEN conductor. The PEN conductor should be connected to the terminal (busbar) which is used to connect the protective conductors. Behind the PEN conductor separation point, protective and neutral conductors must not be connected together.

Secondly, the PEN conductor has the function of transmitting electrical energy. Therefore, it must comply with the requirements for a neutral conductor.

The dual function of the PEN conductor imposes the following limitations:

  • The cross-section of the PEN conductor must be at least 10 mm2 for copper and 16 mm2 for aluminum;
  • The PEN conductor may only be used in fixed wiring;
  • The PEN conductor must be insulated. Its insulation must correspond to the highest voltage for which the electrical circuit containing the PEN conductor is designed;
  • The use of extraneous conductive parts as a PEN conductor is prohibited.

In the electrical installations of buildings, portable and mobile current-using equipments are almost always used, which are connected to fixed wiring by means of flexible connection cables. Since the PEN conductor can only be in fixed wiring, the flexible connection cable of any Class I current-using equipment must have a protective conductor which is connected to its exposed-conductive part and to the protective contacts of the plug. The plug must also have protective contacts which are connected to a protective conductor originating from the PEN conductor of the fixed wiring.

The Electricity Safety, Quality and Continuity Regulations 2002 came into force in the UK on 31.01.2003, paragraph 8 (4) of which declares:

A consumer shall not combine the neutral and protective functions in a single conductor in his consumer’s installation.

The Electricity Safety, Quality and Continuity Regulations 2002

That is, the requirements of the Safety Regulations prohibited the use of PEN conductors in consumer installations (in the electrical installations of buildings). Similar requirements were introduced in the previous standard BS 7671:2001 as part of Amendment 2 to this standard and came into force on 31.03.2004.

Colour, Alphanumeric Notation and Graphical Symbol Used for Identification of PEN Conductors

A PEN conductor, when insulated , shall be identified by one of the following methods [clause 6.3.3 IEC 60445-2021]:

  • GREEN-AND-YELLOW coloured insulation throughout its length and with BLUE colour markings at the terminations and points of connection ; or
  • BLUE coloured insulation throughout its length and with GREEN-AND-YELLOW coloured markings at the terminations and points of connection.

The method to be applied within a country should be decided by the National Committee and not on an individual basis.
The BLUE coloured markings at the termination and points of connection may be omitted provided one of the following two conditions is met:

  • in electrical equipment, if relevant requirements are included in specific product standards or within a country;
  • in the case of wiring systems, for example those used in industry, if decided by the relevant committee.

According to clause 7.3.4 IEC 60445-2021 the alphanumeric identification of a PEN conductor shall be “PEN”.

PEM, PEN conductor identification
PEN conductor identification

References

  1. IEC 60050-195:2021
  2. IEC 60364-4-41:2005
  3. IEC 60364-4-44:2007
  4. IEC 60364-1:2005
  5. IEC 60364-5-54:2011
  6. IEC 60364-7-708:2017
  7. IEC 60364-7-709:2012
  8. IEC 60364-7-710:2021
  9. IEC 60445:2021