Line Conductor Definition and Meaning
Line conductor (identification: L): conductor which is energized under normal conditions and used for the transmission of electric energy but which is not a neutral conductor or mid conductor (defined in the IEC 60445:2021 ). The line conductor in AC electrical circuits is the phase conductor, and in DC electrical circuits is the pole conductor.
Separately distinguished is the earthed line conductor (LE), which is a line conductor that has an electrical connection to the local earth.
Line conductors together with neutral conductors and PEN conductors are used in AC electrical circuits of low-voltage electrical installations, and together with mid-point conductors and PEM conductors – in their DC electrical circuits to provide electrical power to AC and DC electrical equipment.
In my opinion, the important features that relate to linear conductors are most fully described by Kharechko Y.V. in his book :
« A line conductor is considered a live part because it is normally energized under normal conditions and can pose a serious hazard to humans and animals. If a person accidentally touches a line conductor, he or she may be electrocuted or fatally injured. Linear conductors must therefore be insulated to prevent direct contact and thus protect humans and animals from electric shocks. A line conductor is a conductor that is counted in the total number of conductors used in an electrical circuit, network or system. »
Also Kharechko, based on the requirements of IEC 60038:2009, describes the values of voltages under which a linear conductor can be :
« According to the requirements of IEC 60038:2009 the voltage under which a line conductor is relative to ground, neutral conductor or PEN conductor, in three-phase electrical installations of buildings is usually 230 V. The voltage between the line conductors of the different phases is 400 V. In some low-voltage installations, higher voltages may be used: 400 V between the line conductor and ground and 690 V between the line conductors of different phases, and 1000 V between the line conductors. In three-wire circuits in single-phase installations, the voltage between a phase conductor and earth, neutral conductor or PEN conductor is 220 V, and between line conductors 440 V (such low-voltage installations are common, for example, in North America). »
In three-wire DC electrical circuits, the nominal voltage of the line conductor relative to ground, the mid-point conductor, or the PEM conductor is usually 220 V, and between the line conductors of different poles is 440 V. In two-wire electrical circuits, the voltage between the line conductors is 220 V, respectively.
The voltages that line conductors can carry are a serious hazard to humans and animals. If a person accidentally touches a line conductor, he or she may be electrocuted or fatally injured. Linear conductors must therefore be insulated to prevent direct contact and thus protect humans and animals from electric shocks.
Line conductors are also used in ultra-low voltage electrical circuits where the voltage between them does not exceed 50 VAC and 120 VDC. Under these conditions, line conductors are generally not hazardous to humans or animals.
IEC 60364-5-52-2009  specifies requirements for line conductors. Table 52.2 of this standard sets the minimum cross-sections of phase conductors in AC circuits and pole conductors in DC circuits:
|Type of wiring system||Use of the circuit||Conductor|
|Material||Cross-sectional area, mm2|
|Fixed Installations||Cables and insulated conductors||Power and lighting circuits||Copper||1,5|
|Aluminium||To align with cable standard IEC 60228 (10 mm2) (see note 1)|
|Signalling and control circuits||Copper||0,5 (see note 2)|
|Bare conductors||Power circuits||Copper||10|
|Signalling and control circuits||Copper||4|
|Connections with flexible insulated conductors and cables||For a specific appliance||Copper||As specified in the relevant IEC standard|
|For any other application||0,75a|
|Extra-low voltage circuits for special applications||0,75|
NOTE 1. Connectors used to terminate aluminium conductors should be tested and approved for this specific use.
NOTE 2. In signalling and control circuits intended for electronic equipment a minimum cross-sectional area of 0,1 mm2 is permitted.
NOTE 3. For special requirements for ELV lighting see IEC 60364-7-715.
NOTE 4. In the UK, 1,0 mm2 cable is allowed for use in lighting circuits.
NOTE 5. In the UK 1,0 mm2 copper cable is allowed for fixed installations utilizing cables and insulated conductors for power and lighting circuits.
a In multi-core flexible cables containing 7 or more cores, NOTE 2 applies.
Overcurrent Protection Requirements
IEC 60364-4-43:2008  contains requirements for protection of line conductors from overcurrent.
Kharechko Y.V. conducted research work and updated these requirements in his book :
« In  it is prescribed to protect line conductors in electrical installations of buildings with overcurrent protection devices (fuses, circuit breakers, their combinations, etc.), ensuring timely disconnection of overload currents and short-circuit currents to eliminate or significantly reduce their negative impact on conductors. »
« Overload and short-circuit protection devices are usually installed at points in electrical circuits where, due to changes in the cross-section, construction or material of conductors, or the method of laying them, the values of permissible continuous currents of conductors are reduced. »
Clause 433.3.3  does not recommend installing overcurrent protection devices in electrical circuits supplying electrical equipment whose tripping could result in a safety hazard. Such electrical circuits include, for example, excitation circuits of electric machines, electrical circuits supplying hoisting electromagnets, secondary circuits of current transformers. In these cases, the national standard prescribes the installation of alarm devices.
431.1.1  states that for each line conductor, overcurrent detection and disconnection must be provided. However, it is not required to disconnect the other current-carrying conductors of this electrical circuit. However, if disconnection of one phase could cause a hazard, e.g. in the case of a three-phase electric motor, appropriate precautions must be taken.
The regulatory requirements considered are formulated in relation to the use of fuses, which are single-pole overcurrent protection devices that reliably protect line conductors from overloads and short-circuits. However, the protection of the line conductors of three-phase electrical circuits by fuses inevitably leads to incomplete operation of the three-phase electrical consumers included in these circuits.
Incomplete-phase operation of some types of three-phase electrical consumers, such as electric motors, can be accompanied by a reduction in safety, economic losses and other negative consequences. Therefore, in three-phase electrical circuits protected by fuses, special devices are used to monitor the integrity of the fuse links and to signal when they are blown. Having received a signal, maintenance personnel replace the blown fuse with a new one, thus eliminating the three-phase electrical equipment partial-phase operation.
The partial-phase operation is not possible with three- or four-pole circuit breakers protecting three-phase electrical circuits. In the event of a short-circuit or overload in one of the phases, these circuit breakers will open the circuits of all current-carrying conductors. For this reason, the use of multi-pole circuit breakers to protect multi-phase electrical circuits is preferable to the use of fuses.
According to IEC 60445:2021 , alphanumeric identification of a line conductor shall start with the letter “L” suffixed by:
- in AC systems, a sequential number of line conductors, starting with the digit one “1 “;
- in DC systems, with the sign “+” (PLUS SIGN) for the positive line conductor and with the sign “−” (MINUS SIGN) for the negative line conductor.
If no more than one line conductor is used, the suffix may be omitted.
The diagram below shows the line conductors L1, L2, L3 as an example:
- IEC 60364-1
- 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.
- IEC 60364-5-52-2009
- IEC 60364-4-43:2008
- IEC 60445:2021