Protective Conductor (PE): What Is it? (Designation, Cross-section, Requirements)

Protective conductor (identification: PE): conductor provided for purposes of electrical safety (source IEC 60050-195:2021 [1]). In the United States of America, instead of the more correct term “protective conductor” they mostly use the terms “equipment grounding conductor” and “grounding electrode conductor”. It is not a current-carrying conductor and should never be energized under normal conditions.

The terms “equipment grounding conductor” and “grounding electrode conductor” are used in the US depending on their application.

Application

On the application of protective conductors, most capaciously, in my opinion, wrote Kharechko Y.V. in his book [3]:

« Protective conductors are used in low-voltage electrical systems both AC and DC, as well as in electrical installations of buildings that are part of these systems. »

The following are specific examples of the use of protective conductors in various systems.

In TN-S AC and DC systems, such as shown in Figures 31A1 and 31H, respectively, the protective conductors “start” from the earthed live parts of the power supplies.

TN-S system 3-phase, 4-wire with separate the neutral conductor and the protective conductor throughout the distribution system
Figure 31A1 [2] – TN-S system 3-phase, 4-wire with separate the neutral conductor and the protective conductor throughout the distribution system
TN-S DC 3-wire system
Figure 31H [2] – TN-S DC 3-wire system

In TN-C-S AC systems, as for example shown in Figure 31B1, the protective conductors “start” at the points of separation of the PEN conductors into protective and neutral conductors. In TN-C-S AC systems the protective conductors may also “start” from the points at which the PEL conductors are separated into protective and phase conductors (see Figure 1).

In TN-C-S DC systems, as shown in Figure 31K, the protective conductors “start” at the points of separation of the PEL conductor into protective and pole conductors and the PEL conductor into protective and mid conductors.

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 [2] – 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 single-phase two-wire system with separation of PEL conductor into an earthed line conductor and protective conductor for part of the installation
Figure 1 [3] – TN-C-S single-phase 2-wire system with separation of PEL conductor into an earthed line conductor and protective conductor for part of the installation
TN-C-S DC three-wire system
Figure 31K [2] – TN-C-S DC 3-wire system

In TT systems (Figures 31F1 and 31L) and AC and DC IT systems (Figure 31M), protective conductors “start” from the grounding devices of low-voltage electrical installations.

TT system 3-phase, 4-wire with the neutral conductor throughout the distribution system
Figure 31F1 [2] – TT system 3-phase, 4-wire with the neutral conductor throughout the distribution system
TT DC three-wire system
Figure 31L [2] – TT DC 3-wire system
DC IT system three-wire
Figure 31M [2] – DC IT system 3-wire

1) The system may be connected to earth via a sufficiently high impedance. This connection may be made, for example, at the mid conductor or the pole conductor.

NOTE. Additional earthing of the protective conductor in the electrical installation may be provided.

Examples of Protective Conductors and their Purpose

Examples of a protective conductor include a protective bonding conductor, a protective earthing conductor and an earthing conductor when used for protection against electric shock [4].

The protective conductors are also PEN-, PEM– and PEL-conductors, which, firstly, serve as protective earthing conductors and, secondly, as neutral, mid and line conductors.

Let’s refer to the book [3], the author of which Y.V. Harechko describes the purpose of various protective conductors in more detail:

« The protective conductors, PEN-, PEM- and PEL-conductors in the TN-C, TN-S and TN-C-S systems connect the exposed conductive parts of class I equipment used in electrical installations of buildings to the earthed live parts of the power supplies. As any of these electrical conductors must be grounded at the point of entry into a building installation, protective conductors, PEN-, PEM- and PEL-conductors are used to connect exposed conductive parts of class I equipment to the grounding devices of building installations. By means of protective conductors in electrical installations of buildings corresponding to the TT and IT system earthing types, the exposed conductive parts of class I equipment are connected to the earthing devices of electrical installations of buildings. »

The protective bonding conductors in buildings are used to electrically connect external conductive parts to each other and to connect them to the earthing devices of the electrical installations of buildings. When carrying out additional equipotential bonding, protective bonding conductors connect exposed conductive parts of class I equipment with external conductive parts in rooms of the building which are characterized by increased danger, e.g. have conductive floors.

Figure 2 is a schematic illustration of the types of protective conductors used in a building installation and the main types of conductive parts to which protective conductors are connected.

Grounding and protective conductors
Figure 2 – Grounding and protective conductors

Figure 2 shows:

  • 1 – protective conductor (circuit protective conductor in United Kingdom);
  • 2 – main protective bonding conductor;
  • 3 – grounding conductor;
  • 4 – supplementary protective bonding conductor;
  • B – main earthing clamp;
  • M – exposed conductive part;
  • C – third-party conductive part;
  • P – metal plumbing pipe;
  • T – earth electrode.

Figure B.54.1 shows the protective conductor arrangement in more detail [4]:

Example of earthing arrangements and protective conductors
Figure B.54.1 – Examples of earthing arrangements for foundation earth electrode, protective conductors and protective bonding conductors

Figure 3 shows:

  • C – Extraneous-conductive-part;
  • C1 – Water pipe, metal from outside (or district heating pipe);
  • C2 – Waste water pipe, metal from outside;
  • C3 – Gas pipe with insulating insert, metal from outside;
  • C4 – Air-conditioning;
  • C5 – Heating system;
  • C6 – Water pipe, metal e.g. in a bathroom (see IEC 60364-7-701 701.415.2:2006);
  • C7 – Waste water pipe, metal e.g. in a bathroom (see IEC 60364-7-701 701.415.2 dated 2006);
  • D – Insulating insert;
  • MDB – Main distribution board;
  • DB – Distribution board;
  • MET – Main earthing terminal;
  • SEBT – Supplementary equipotential bonding terminal;
  • T1 – Concrete-embedded foundation earth electrode or soilembedded foundation earth electrode;
  • T2 – Earth electrode for LPS if necessary;
  • LPS – Lightning protection system (if any);
  • PE – PE terminal(s) in the distribution board;
  • PE/PEN – PE/PEN terminal(s) in the main distribution board;
  • M – Exposed-conductive-part;
  • 1 – Protective earthing conductor (PE);
  • 1a – Protective conductor, or PEN conductor, if any, from supplying network;
  • 2 – Protective bonding conductor for connection to the main earthing terminal;
  • 3 – Protective bonding conductor for supplementary bonding;
  • 4 – Down conductor of a lightning protection system (LPS) if any;
  • 5 – Earthing conductor.

NOTE. Functional earthing conductors are not shown in Figure B.54.1

Requirements

Since protective conductors are used as part of measures to protect against electric shock, special requirements are imposed on their characteristics, performance and technical condition by regulatory and legal documents.

About the basic requirements for protective conductors writes Kharechko Y.V. in his book [3]:

« One of the main requirements for protective conductors is to ensure continuity of their electrical circuits. IEC 60364-5-54-2011 (Clause 543.3.3) prohibits the inclusion of switching devices in the electrical circuits of protective conductors. The exception – plug sockets and plugs, through which carry out the connection of portable, mobile and other electrical equipment of class I with a detachable connection to fixed electrical wiring. Electrical circuits of protective conductors in plug and socket connections shall be severed together with the electrical circuits of phase conductors and neutral conductor, pole conductors and mid conductor. »

However, the requirements of [4] allow the protective conductor circuits to have detachable connections that can be disassembled with a tool to perform the necessary tests. Connections of protective conductors must be accessible for inspection and testing, except for connections filled with compound or sealed.

Protective conductors shall be suitably protected against mechanical damage, chemical or electrochemical deterioration, electrodynamic forces and thermodynamic forces.

[543.3.1, 4]

Particular attention should be paid to the correct wiring of plug sockets, as this can connect their protective contacts in series in the circuit of the protective conductor.

Y.V. Harechko in his book [2] explains this “case” in more detail:

« Modern two-pole receptacles used in single-phase electrical circuits usually have two spring clips each for connecting a phase conductor, a neutral conductor and a protective conductor. When connecting the protective conductor of the wiring harness to the first terminal of the protective contact of the first plug socket, connecting the conductor of the first terminal of the protective contact of the second plug socket to the second terminal of the protective contact of the first, the first terminal of the protective contact of the third plug socket to the second terminal of the protective contact of the second, etc. the protective contacts of the plug sockets will be connected in series with the protective conductor.

If the sockets are connected by a loop, the connection of their protective contacts must be made to the branches from the protective conductor of the fixed wiring, which are usually made in junction boxes. »

Important facts [3, 4]:

  1. The use of a protective conductor of an electrical instal lation for signal l ing is not al lowed (IEC 61140-2016).
  2. It is not intended to connect every individual protective conductor directly to the main earthing terminal where they are connected to this terminal by other protective conductors.
  3. The exposed conductive parts of the electrical equipment must be connected to the terminal designed for the protective conductor.
  4. If overcurrent protection devices are used to protect against electric shock as part of an automatic power failure, protective conductors made with solid wires should be laid in common sheath with the line conductors or in close proximity to them.

Protective conductors may consist of one or more of the following: [4]:

  • conductors in multicore cables;
  • insulated or bare conductors in a common enclosure with live conductors;
  • fixed installed bare or insulated conductors;
  • metallic cable sheath, cable screen, cable armour, wirebraid, concentric conductor, metallic conduit, subject to the conditions stated in 543.2.2. a) and b).

The following metal parts are not permitted for use as protective conductors or as protective bonding conductors [4]:

  • metallic water pipes;
  • metallic pipes containing potentially flammable materials such as gases, liquids, powder;
  • constructional parts subject to mechanical stress in normal service;
  • flexible or pliable metal conduits, unless designed for that purpose;
  • flexible metal parts;
  • support wires; cable trays and cable ladders.

As established by [4], exposed conductive parts of one electrical equipment, except for switchgear and bus ducts, may not be used as protective conductors for other electrical equipment. It is prohibited to connect exposed conductive parts of class I equipment in series to a protective conductor. Each exposed conductive part of class I equipment must be connected by a separate protective conductor which is formed, for example, as a branch from the protective conductor of the fixed wiring in a pullout, junction or junction box.

Color and alphanumeric identification

The following requirements are in accordance with [5].

The protective conductor shall be identified by the bi-colour combination GREEN-AND-YELLOW.

GREEN-AND-YELLOW is the only colour combination recognized for identifying the protective conductor.

The colour combination GREEN-AND-YELLOW shall be such that, on any 1 5 mm length of the conductor where colour coding is applied, one of these colours covers at least 30 % and not more than 70 % of the surface of the conductor, the other colour covering the remainder of that surface.

If bare conductors used as protective conductors are provided with colouring they shall be coloured GREEN-AND YELLOW, either throughout the whole length of each conductor or in each compartment or unit or at each accessible position. If adhesive tape is used, only bi-coloured GREEN-AND-YELLOW tape shall be applied.

Where the protective conductor can be easily identified by its shape, construction or position, for example a concentric conductor, colour coding throughout its length is not necessary but the ends or accessible positions should be clearly identified by the graphical symbol IEC 60417-5019 (2006-08) “Protective earth; protective ground”,

Identification of the protective conductor

or the bi-colour combination GREEN-AND-YELLOW or the alphanumeric notation PE.

If extraneous-conductive-parts are used as a protective conductor, identification by colours is not necessary.

NOTE 1. In Canada, the colour identification GREEN for the protective conductor is used as a replacement for the colour combination GREEN-AND-YELLOW.

NOTE 2. In Japan, GREEN or GREEN-AND-YELLOW can be used as the colour identification for the protective conductor.

NOTE 3. In the United States, the colour identification GREEN for the protective conductor is used as a replacement for the colour combination GREEN-AND-YELLOW.

NOTE 4. In the United States, the use of the single colour GREEN is permitted for identification of protective earth conductors.

NOTE 5. In the United States, identification of the equipment grounding conductor is only by coloration of green or green with yellow stripes. In the US, identification of the equipment grounding conductor is made by GREEN or GREEN with one or more YELLOW stripes for the insulation, other means of coloration, coloured tape or adhesive labels, or stripping the insulation or covering from the entire exposed length of the conductor.

The alphanumeric identification of a protective conductor shall be “PE”. This identification also applies for a protective earthing conductor.

Cross-section of the protective conductor

Cross-section of the protective conductor is selected according to Table 54.2 [4]:

Minimum cross-sectional area of protective conductors (where not calculated in accordance with 543.1.2 [4])
Cross-section of copper line conductors S, mm2 Minimum cross-section of the corresponding protective conductor made, mm2
of copper other metals
S ≤ 16 S (k1/k2)*S
16 < S ≤ 35 16a) (k1/k2)*16
S > 35 S/2a) (k1/k2)*(S/2)

k1 – is the value of k for the line conductor derived from the formula in Annex A or selected from tables in IEC 60364-4-43, according to the materials of the conductor and insulation;

k2 – is the value of k for the protective conductor, selected from Tables A.54.2 to A.54.6 [4] as applicable.

a) For a PEN conductor, the reduction of the cross-sectional area is permitted only in accordance with the rules for sizing of the neutral conductor (see IEC 60364-5-52)

Or calculate in accordance with clause 543.1.2 of [4]. The cross-sectional areas of protective conductors shall be not less than the value determined either:

  • in accordance with IEC 60949; or
  • by the following formula applicable only for disconnection times not exceeding 5 s:
Protective conductor cross-section formula

where

  • S – is the cross-sectional area in mm2;
  • I – is the r.m.s value expressed in amperes of prospective fault current, for a fault of negligible impedance, which can flow through the protective device (see IEC 60909-0);
  • t – is the operating time in seconds of the protective device for automatic disconnection;
  • k – is the factor dependent on the material of the protective conductor, the insulation and other parts and the initial and final temperatures (for calculation of k, see Annex A).

Where the application of the formula produces a non-standard size, a conductor having at least the nearest larger standard cross-sectional area shall be used.

NOTE 1. Account should be taken of the current-limiting effect of the circuit impedances and the limitation of I²t of the protective device.
NOTE 2. For limitations of temperatures for installations in potentially explosive atmospheres, see IEC 60079-0.
NOTE 3. As the metallic sheaths of mineral-insulated cables according to IEC 60702-1 have an earth fault capacity greater than that of the line conductors, it is not necessary to calculate the cross-sectional area of the metallic sheaths when used as protective conductors.

Important! In accordance with clause 543.1.3 of [4] the cross-sectional area of every protective conductor which does not form part of a cable or which is not in a common enclosure with the line conductor shall be not less than

  • 2,5 mm2 Cu or 16 mm2 Al if protection against mechanical damage is provided,
  • 4 mm2 Cu or 16 mm2 Al if protection against mechanical damage is not provided.

NOTE. The use of steel for a protective conductor is not excluded (see 543.1.2).

A protective conductor not forming part of a cable is considered to be mechanically protected if it is installed in a conduit, trunking or protected in a similar way.

In accordance with clause 543.1.4 of [4] where a protective conductor is common to two or more circuits, its cross-sectional area shall be:

  • calculated in accordance with 543.1.2 for the most onerous prospective fault current and operating time encountered in these circuits; or
  • selected in accordance with Table 54.2 so as to correspond to the cross-sectional area of the largest line conductor of the circuits.

References

  1. IEC 60050-195:2021
  2. IEC 60364-1
  3. 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.
  4. IEC 60364-5-54-2011
  5. IEC 60445-2021