Protective conductor

Color coding of protective conductors

Symbol for the protective conductor

A protective conductor is an electrical conductor for the purpose of safety, for example to protect against electric shock . The abbreviation for the protective conductor is PE ( English protective earth ). The task of the protective conductor in electrical systems is to protect living beings in the event of a fault.

Basics

The protective measure protective earthing of electrical engineering systems serves to keep this at earth potential in the event of a short between an active (live) conductor and a conductive, touchable part (e.g. the housing) and thus a current flow through the (human) body to earth to prevent or at least reduce it. For this purpose, all accessible metal parts of protection class I devices are connected to earth using the protective conductor. The basic protection (protection against direct contact with an active part) is the isolation between touchable conductive part and the dangerous voltage. If this fails, the fault protection takes effect (protection against indirect contact in the event of failure of the basic insulation). The protective conductor is therefore a prerequisite for the two sub-measures "Protective earthing and protective equipotential bonding" (previously " Zeroing ") and "Automatic shutdown in the event of a fault". The protective conductor forms a circuit in the event of a fault and causes the overcurrent protective device to respond.

For final circuits with a nominal current of up to 32 A, maximum switch-off times of 0.4 seconds are specified for the conventional 230/400 V TN AC network .

Is decisive for the protective device that meet the circuit impedances following requirements: . It is ${\ displaystyle Z_ {S} \ leq {\ frac {U_ {0}} {I_ {a}}}}$

${\ displaystyle Z_ {S}}$ the sum of all impedances in the fault loop (power source, external conductor, protective conductor circuit),
${\ displaystyle I_ {a}}$ the current required for automatic shutdown,
${\ displaystyle U_ {0}}$ the nominal voltage for the circuit, outer conductor to earth.

The shutdown is carried out by overcurrent protective devices ( circuit breakers , fuses , miniature circuit breakers ) and can be supplemented by residual current circuit breakers (RCDs).

Standardization in Germany

The current DIN VDE 0100-410 “Setting up low-voltage systems - protective measures; Protection against electric shock ”prescribes a series of measures to protect against electric shock. In principle, DIN VDE requires that a protective measure consists of a suitable combination of two independent protective measures. This is usually a basic security precaution and an error protection precaution.

The prerequisites for the "automatic shutdown in the event of a fault" are made up of precautions that must be met by the distribution network operator and the installation regulations for the customer system, which are specified in DIN VDE 0100-540 "Installation of low-voltage systems - selection and installation of electrical equipment - earthing systems "Protective conductor and protective equipotential bonding conductor " are specified.

In addition to defining terms, the technical design of earthing systems and the criteria for earth electrodes, earthing conductors and protective equipotential bonding conductors, this standard specifies essential design features for the protective conductor such as minimum cross-sections, types of protective conductors, arrangement of protective conductors and measures to maintain the electrical properties of protective conductors.

Historical development

The protective conductor in the form and application as we know it today is preceded by a long development in terms of methods for earthing and zeroing, and finally the introduction of the “ special conductor as protective conductor” and a long decision-making process with regard to color.

The protective measure “zeroing” goes back to a proposal by AEG in November 1913, and in 1924 zeroing is mentioned in the forerunners of VDE 0100. At the same time, the term “ neutral conductor ” (spelling at the time: neutral conductor ) was introduced, but without describing it in more detail. In 1930 the neutral conductor was defined and the term “special zeroing line” (the forerunner of today's protective conductor) was used. VDE 0488/1930 requires "a special plug device with protective contact " for the connection of portable equipment . This requirement was valid until 1958 as VDE 0140: 1932.

In VDE 0100: 1936, Section 2 h), the neutral conductor is described as a conductor that is connected to the neutral point. According to VDE 0100: 1936, Section 2 g), zeros define the establishment of a conductive connection to the earthed neutral conductor. The neutral conductor at that time corresponds to the PEN conductor in what is now known as the TN-C system . With VDE 0100 / 11.58, § 10 b.9 (with pictures), the “special protective conductor” for the “permanently installed part of the system” is treated as a possible installation in the VDE for the first time .

A completely different topic is the color of the cables, which was very individual nationally until 1965 and, according to various sources, provided for a red color coding for the protective conductor in Germany, Austria, Switzerland (and other countries). It should be noted that the red color coding was not reserved for the protective conductor alone. A red marked conductor could also be a switched outer conductor or L2 in the three-wire AC network , but not the PEN.

Until 1964, the protective conductor was red-yellow in Switzerland, since then it has been yellow-green.

As far as the protective conductor is concerned, there was only a major change in the standard in 1965. Up until this point there was no green / yellow insulated wire. The initial specifications for this can be found in VDE 0100 / 12.65, § 10N, b 9.1 for the protective conductor and in VDE 0100 / 12.65, § 10N, b 8.1 for the neutral conductor (today PEN conductor).

Starting in 1958, there were first talks between the EC countries on the subject of harmonizing the "electrotechnical regulations" . As a result, with CENELCOM, founded in 1959 (the predecessor of CENELEC , the European Committee for Electrotechnical Standardization), the harmonization of wire colors between the member countries began. The introduction of the green-yellow protective conductor and the harmonization of the wire colors for flexible cables were partial successes.

The suggestion of a green-yellow marking for the protective conductor goes back to Obering. Karl Kling (AEG central assembly in Berlin and Frankfurt am Main), chairman of the committee for safety regulations 1962–1978, as a letter dated September 8, 1956 from Dr. Hans Walther (at that time AEG factory management) can be found. The documents for the creation of the protective conductor in green and yellow are collected in the VDE archive in folder 1022. Further evidence of the beginnings of the green-yellow marking of the protective conductor can be found in the article "The new green-yellow protective conductor marking " by Theodor Wasserburger in ETZ-B - Elektrotechnische Zeitung, Edition B, Volume 13 (1961) H. 6 (VDE -Archive).

The green and yellow marking is used to make the protective conductor clearly recognizable even in poor lighting conditions.

Since December 1, 1965, a green-yellow wire may only be used as a protective conductor (or as a PEN) and for nothing else.

In the current DIN VDE 0100-200: 2006-06, the protective conductor (designation: PE) is defined under item 826-13-22 as follows: "Conductor for the purpose of safety, for example to protect against electric shock [IEV 1 95- 02-09] ".

Execution and marking

Symbol for the protective conductor connection in accordance with DIN EN 60617-2

Transition from old to new color coding in Germany:
outer conductor from black to brown;
Neutral conductor from light gray to blue;
Protective conductor from red to green / yellow.

The essential provisions regarding the design and marking of the protective conductor can be found in the relevant standards; in Germany this is DIN VDE 0100-540. There, as in Switzerland, a protective conductor must be marked with the color combination green / yellow over the entire length. This color combination may only be used for conductors with a protective conductor function (i.e. also for PEN conductors ) and for no other purpose . Any unused green / yellow insulated conductors in multi-core lines or cables must not be used for purposes other than those intended and may not be used. According to EN 60204-1, single conductors in the colors GREEN or YELLOW are not generally prohibited, but the following stipulation from point 13.2.4 must be observed:

"For safety reasons, the colors GREEN or YELLOW should not be used where there is a possibility of confusion with the two-color combination GREEN-YELLOW."

For different wire colors of the protective conductor in Germany before 1965: See section Historical development above.

For protective conductors, minimum cross-sections must be observed that meet the condition for automatic shutdown in the event of a fault (IEC 60949) taking into account all effective circuit impedances.

In addition, for cables and lines with outer conductors and a cross-section up to and including 16 mm², the protective conductor must be the same as the cross-section of the outer conductor. For outer conductors up to 35 mm² the protective conductor may have a cross-section of 16 mm² and for outer conductors with a cross-section> 35 mm² the protective conductor must have at least half of this cross-section. This regulation only applies to protective conductors (PE) and is not applicable to PEN conductors.

At plug connectors , the protective conductor is connected to special protective contacts which are arranged in such a way that they are connected before the other contacts and separated after the other contacts.

Protective conductor connections on devices and plugs are to be made in such a way that the protective conductor only loosens from the connection point when the connection cable is pulled strongly when all active (live) conductors have already been disconnected. This is usually achieved by shortening the other wires or positioning the connections in such a way that the protective conductor can be laid in a loop so that it is not stretched even when the other wires are already pulled tight.

Devices that are protected by protective insulation do not require a protective conductor. Connection cables that contain a protective conductor are permitted.

Further protective measures (Germany, DIN)

The protective conductor is part of the protective measure fault protection - protection against direct contact , which includes the measures protective grounding (grounding via the protective conductor) , protective grounding via the main earthing rail (also known as local equipotential bonding ) and the measure automatic shutdown in the event of a fault . According to the general rules of technology, one or more protective measures (taking into account all influences) must be applied in an electrical system (DIN VDE 0100-410 section 410.3.3).

In addition to fault protection with automatic shutdown in the event of a fault (or instead of), the following protective measures are generally permitted:

Protection through double or reinforced insulation ; a protection insulation (Class II) prevents the direct contact with the metal casing, either by a plastic housing or by an additional insulation inside.
Protection through protective separation for the supply of electrical system parts, e.g. B. by separation with an isolating transformer .
Protection through low voltage using SELV or PELV .

Exam (Germany)

During the test, there is always between testing an electrical system in accordance with DIN VDE 0100-600 (e.g. for normal house installations; repeat test in accordance with DIN VDE 0105) and testing electrical devices for domestic use (portable electrical equipment) in accordance with DIN VDE 0701-0702 to distinguish.

When testing electrical systems, the protective conductors including the equipotential bonding conductors are checked for continuity. The previously applicable limit value of 1 ohm for protective conductors and equipotential bonding conductors is no longer applicable (DIN VDE 0100-600 "61.3.2 Continuity of conductors"). According to the standard, the expected value is to be used as the limit value. An expected value must be determined by calculation. The following parameters are to be used when calculating the resistance value:

specific resistance of the conductor
Length of the conductor
Contact resistance of the contact points

The expected value is in the initial test acc. To document DIN VDE 0100-600. In the case of repeat tests, this value is used as the basis for evaluating the protective conductor and equipotential bonding connection. To prove the effectiveness of the protective measures of the indirect contact protection, the loop impedance must be determined and the fulfillment of the switch-off condition checked. For TN networks, DIN VDE 0100-600 table NA.1 disconnection conditions in the TN network is to be used.

For the functional test of the protective conductor connection of electrical devices for domestic use, a test current of 200mA (10A is no longer permissible) from a voltage source with an open circuit voltage of up to 12 volts is applied to each accessible metal part against the protective conductor contact in accordance with DIN EN 701-702 and the protective conductor resistance is calculated calculated from the measured voltage drop and the test current. This may be a maximum of <0.3 Ω for devices with a mains connection cable (for further details, see the specified standard).

The test of the protective conductor connection on machines according to EN 60204 also relates to DIN VDE 0100-600 for the initial test and thus corresponds to the procedure for testing the electrical system. No specific values are set here. The protective conductor resistance must correspond to the value that is to be expected according to the conductor cross-section and conductor length.

literature

Alfred Hösl, Roland Ayx, Hans Werner Busch: The correct electrical installation . 18th edition. Hüthig, Heidelberg 2003, ISBN 3-7785-2909-9 .
Dieter Vogt, Herbert Schmolke: Electrical installation in residential buildings . 6th edition. VDE Verlag, Berlin / Offenbach 2005, ISBN 3-8007-2820-6 .
M. Kampler, H. Nienhaus, D. Vogt: Testing before commissioning of low-voltage systems (= VDE series of publications . Volume 63 ). 3. Edition. VDE Verlag, Berlin / Offenbach 2008, ISBN 978-3-8007-3112-1 .
Wilhelm Rudolph: Introduction to DIN VDE 0100, electrical systems in buildings (= VDE series of publications . Volume 39 ). 2nd Edition. VDE Verlag, Berlin / Offenbach 1999, ISBN 3-8007-1928-2 .

Norms

HD 60364-1 (IEC 60364-1 modified; VDE 0100-100) Installation of low-voltage systems - Part 1: General principles, provisions for general characteristics, terms
DIN VDE 0100-200 (IEC 60050-824 modified) Erection of low-voltage systems - Part 200: Terms
HD 60364-41-1 (IEC 60364-41-1 modified; VDE 0100-410) Erection of low-voltage systems - Part 4-41: Protective measures - Protection against electric shock
HD 60364-5-54 (IEC 60364-5-54; VDE 0100-540) Installation of low-voltage systems - Part 5-54: Selection and installation of electrical equipment - Part 5-54: Earthing systems and protective conductors
HD 60364-6 (IEC 60364-6 modified; VDE 0100-600) Erection of low-voltage systems - Part 6: Tests
EN 60204-1 (VDE 0113-1) Safety of machines - Electrical equipment of machines - Part 1: General requirements
EN 60335-1 (VDE 0700-1) Safety of electrical devices for household use and similar purposes - Part 1: General requirements

Web links

Wiktionary: Protective conductor - explanations of meanings, word origins, synonyms, translations

Individual evidence

↑ Definition according to DIN VDE 0100-200: 2006-06 section 826-13-22
↑ DIN VDE 0100-410: 2007-06 Section 411.3.2 Automatic shutdown in the event of an error , Table 41.1
^ Wilhelm Rudolph: VDE series 39. Introduction to DIN VDE 0100. 2009, p. 109.
↑ Kölner Rundschau of March 26, 1977, reproduction of information from the DKE telephone service.
↑ Kontrollbuero.ch (PDF)
^ Wilhelm Rudolph: VDE series 39. Introduction to DIN VDE 0100. 2009, p. 536.
↑ On Karl Klinger and Hans Walther: See also history of electrical engineering. Vol. 15, part 1, VDE-Verlag, Berlin / Offenbach 1997, pp. 246, 249 and 256.
^ Wilhelm Rudolph: VDE series 39. Introduction to DIN VDE 0100. 2009, pp. 532-534.
^ Wilhelm Rudolph: VDE series 39. Introduction to DIN VDE 0100 , 2009, p. 534, Fig. 510-10.
↑ The resistance of each protective conductor system between the PE terminal and relevant points that are part of each protective conductor system must be measured with a current of 200mA (10A is no longer permissible). This current can be taken from an electrically isolated supply (e.g. SELV, see IEC 60364-4-41, 413.1) with a maximum open circuit voltage of AC 24 V or DC 24 V.

[1] Definition according to DIN VDE 0100-200: 2006-06 section 826-13-22

[2] DIN VDE 0100-410: 2007-06 Section 411.3.2 Automatic shutdown in the event of an error , Table 41.1

[3] Wilhelm Rudolph: VDE series 39. Introduction to DIN VDE 0100. 2009, p. 109.

[4] Kölner Rundschau of March 26, 1977, reproduction of information from the DKE telephone service.

[5] Kontrollbuero.ch (PDF)

[6] Wilhelm Rudolph: VDE series 39. Introduction to DIN VDE 0100. 2009, p. 536.

[7] On Karl Klinger and Hans Walther: See also history of electrical engineering. Vol. 15, part 1, VDE-Verlag, Berlin / Offenbach 1997, pp. 246, 249 and 256.

[8] Wilhelm Rudolph: VDE series 39. Introduction to DIN VDE 0100. 2009, pp. 532-534.

[9] Wilhelm Rudolph: VDE series 39. Introduction to DIN VDE 0100 , 2009, p. 534, Fig. 510-10.

[10] The resistance of each protective conductor system between the PE terminal and relevant points that are part of each protective conductor system must be measured with a current of 200mA (10A is no longer permissible). This current can be taken from an electrically isolated supply (e.g. SELV, see IEC 60364-4-41, 413.1) with a maximum open circuit voltage of AC 24 V or DC 24 V.