Neutral conductor

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Current color coding of neutral conductors
EU blue
Switzerland Light Blue(preferred)
blue(alternative)
Canada White
United States White
Gray
Australia,
New Zealand		 black

In the low-voltage network for electrical energy, a neutral conductor is a conductor that is electrically connected to the neutral point and is able to contribute to the distribution of electrical energy.

Marking and execution

The neutral conductor is designated with the letter N in Europe.

According to the IEC 60446 standard used in the European Union and Switzerland , neutral conductors must be marked with the color blue over their entire length. According to NIN 2010, light blue is preferred in Switzerland .

The CEE 7/4 type Schuko socket, which is widespread in many European countries, is symmetrical and does not distinguish between the two live conductors, outer conductors and neutral conductors; The assignment is fixed for other sockets, for example those used in Switzerland according to the SEV 1011 standard. A grounding devices connected exclusively via the protective earth (PE).

Contrary to many opinions, there is no standard for CEE 7/4 sockets that defines the position of the neutral conductor “left” or “right” in the case of horizontally arranged sockets. With sockets according to the Swiss standard SEV 1011, the neutral conductor is on the left as seen from the observer and the protective conductor is at the bottom in the middle.

Basics

In Germany, according to the definition in DIN VDE 0100-200 (Section 826-12-08), the neutral conductor is an active conductor, like the outer conductor, and is intended to carry electricity during regular operation. In consumer systems based on TN-C and TN-CS systems, the neutral conductor is considered to be suitably grounded with low resistance if the permissible contact voltage between the neutral conductor and protective conductor is not exceeded under any circumstances, so it does not "need" to be separated (together with the external conductors) become. In Belgium, France, Norway, Portugal, Spain and Switzerland, however, the neutral conductor is not considered to be reliably earthed with a suitably low resistance.

In a three-phase AC network , the current in the neutral conductor cancels out if currents of the same current strength , same phase shift and no harmonic component flow in all three outer conductors . In the case of unequal currents in the outer conductors, a current flows in the neutral conductor that compensates for the asymmetry and, under the above conditions, reaches a maximum of the current of the most heavily loaded outer conductor. With different phase shifts of the currents in the outer conductors, or with harmonics (especially 3rd order) in addition to the fundamental frequency, the current in the neutral conductor can significantly exceed the current of the most heavily loaded outer conductor.

Historical development in Germany

In Germany there was no neutral conductor in the old VDE regulations. In 1958 only the principle of zeroing was used there. The grounded middle conductor was called the neutral conductor (spelling at that time). It had combined the function of the protective conductor and the neutral conductor, so its function corresponded to the current PEN conductor . It was marked with the color light gray.

The term center conductor has existed since 1965 , which for the first time functionally corresponded to today's neutral conductor and was wired in light blue. At the same time, the green / yellow marking for the protective conductor was introduced, the neutral conductor, which was still permitted at that time, was changed in color from light gray to green / yellow.

In 1973 the so-called "classic zeroing" was prevented, and in June 1975 the neutral conductor was renamed PEN.

The wire colors from 1965 remained unchanged until 2003. The current wire color blue (instead of light blue) for the neutral conductor was introduced with DIN VDE 0293-308: 2003-01.
Classic PEN systems can be found in customer installations in Germany that were completed before March 31, 1974 and, according to the current standard, only in the distribution network of the network operator and for special applications. The division of PEN into PE and N conductors takes place today directly at the handover from the network operator to the customer system in the house connection box . The term “neutral conductor” was first mentioned in 1983 in the VDE.

Even today, the neutral conductor is often inappropriately referred to as the neutral conductor, and "gray" is incorrectly stated as the previous wire color, but in both cases it is a conductor that corresponds to the PEN conductor today.

Neutral conductor interruption

Overvoltage on ohmic loads when the neutral conductor is interrupted with three-phase alternating current

In a multi-phase network, e.g. B. a three-phase alternating current network, in the event of an interruption of the neutral conductor ("neutral conductor break"), the resistances of the consumables on the individual outer conductors form a voltage divider , whereby the potential of the now "free" or "floating" star point can shift if the outer conductor is asymmetrically loaded. This unequal load distribution is called unbalanced load . In the case of very unequal currents in the outer conductors, the voltage between the outer conductor with the lowest load and the star point can almost increase to the voltage between two outer conductors. This can lead to overvoltage damage.

According to current standards in Germany, the neutral conductor does not need to be switched. Under no circumstances may the neutral conductor be switched alone, but always together with all active conductors in a circuit and only with standard-compliant devices (with marked N terminals). A circuit-related break in the neutral conductor is therefore excluded.

Special

In contrast to the currents of the fundamental oscillation, the currents of the harmonics in the neutral conductor , which can be divided by three, do not cancel , but add up. With the mains frequency of 50 Hz that is common in Europe, this applies in particular to the third harmonic with 150 Hz and the ninth harmonic with 450 Hz - even harmonic harmonics play no role if there is no DC component. As a result, there is a risk that in systems with several devices that have no or too little power factor correction, such as switched-mode power supplies z. B. from personal computers, televisions or fluorescent lamps with electronic ballasts, the neutral conductor current is above the permissible limits, while the individual outer conductors have not yet reached their maximum current for which the fuse is dimensioned. Newer standards take this into account and contain load tables for the common types of reference installation with columns for different harmonic components of the third harmonic of the external conductor currents.

According to relevant national standards, no single-pole switching devices may be used in the neutral conductor, or single-pole changeover switches must be connected in the (same) outer conductor (which excludes use in the neutral conductor).

Norms

  • DIN VDE 0100-100: 2009-06; Erection of low-voltage systems - Part 1: General principles, provisions of general characteristics, terms.
  • DIN VDE 0100-200: 2006-06; Erection of low-voltage systems - Part 200: Terms.
  • DIN VDE 0100-510: 2011-03; Erection of low-voltage systems - Part 5-51: Selection and erection of electrical equipment - General provisions.
  • DIN VDE 0293-308: 2003-01; Color coding of the cores of cables / lines and flexible lines.

literature

  • Wilhelm Rudolph: Introduction to DIN VDE 0100, electrical systems in buildings . 2nd Edition. tape 39 . VDE Verlag, Berlin and Offenbach 1999, ISBN 3-8007-1928-2 (VDE series of publications).

Individual evidence

  1. ↑ In Germany: Definition according to DIN VDE 0100-200: 2006-06 Section 826-14-07
  2. ↑ Excerpt from NIN 2010, 5.1.4.3.1.1: “ Neutral conductors or center conductors must be marked with the color blue over their entire length ”, with the comment in 5.1.4.3.1.6: “ In international documents (IEC and CENELEC) is for the The color blue (formerly light blue) is provided for the core identification of neutral conductors. This means that blue and light blue are approved for marking neutral conductors. In Switzerland, light blue is preferred for marking neutral conductors. »
  3. ↑ Contrary to the previous practice of connecting the neutral conductor (viewed from the front) on the left with horizontally arranged sockets, the variant with the neutral conductor "right" is becoming more and more popular.
    If the neutral conductor is connected on the right, the frequent use of the "angled plug with the connection cable pointing downwards" ensures compatibility with the French system (type E; CEE7 / 5), for which there are binding national regulations for the connection sequence in France.
  4. ↑ DIN VDE 0100-460: 2002-08 Section 461.2
  5. ↑ VDE 0100 / 11.58 “Condition and laying of lines” § 19
    Lines (insulated and sheathed lines, cables) Marking of wires:
    If a wire is used as a neutral wire, the light gray one must be used for it. If a wire is used as a protective conductor in cables for portable power consumers, the red wire must be used for this.
  6. ↑ VDE 0100 / 12.65, § 10N, b 8.1 Light blue: for the center conductor. (or also in § 3c 2.)
  7. ↑ VDE 0100 / 12.65, § 10N, b 9.1 for the protective conductor, § 10N, b 8.1 for the neutral conductor
  8. ↑ VDE 0100 / 5.73 § 10 a)
    (2.2.) A cross-section of at least 10 mm² Cu must be used for zeroing; (2.1.) For smaller cross-sections, the “special protective conductor” (the forerunner of today's PE) must be laid in addition to the center conductor.
  9. ↑ The application CENELEC 64A (CH) 101/73 of Switzerland from October 1973 was accepted by the TC 64 committee at the conference on June 26th 1975 in Ankara (and thus a term used for 50 years was eliminated, 40 years after the renaming is always used incorrectly on a regular basis).
  10. ↑ DIN VDE 0293-308: 2003-011 Section 3.2 For single-core cables / lines that fulfill neutral conductor functions, the color blue is used for identification.
    DIN VDE 0100-510: 2011-03 Section 514.3.1.Z1 Neutral conductors or center conductors must be marked with the color blue over their entire length.
  11. ↑ DIN VDE 0100-410: 1983-11 and DIN VDE 0100-540: 1983-11, specified for the first time in DIN VDE 0100-200: 1998-06 in section 2.1.3 (published in 12/88 as a draft)
  12. ↑ DIN VDE 100-520 Beiblatt 3: 2012-10 Erection of low-voltage systems - selection and erection of electrical equipment; Part 520: Cable and line systems - Supplement 3: Current carrying capacity of cables and lines in 3-phase distribution circuits for load currents with harmonic components. With columns for 15 ... 33%, 33 ... 45% and> 35% (calculated with 60%)
  13. ↑ VDE 0100-460 section 465.1.2; VDE 0100-550 section 5; ÖVE E8001-2-31 section 31.8.1; NIN (Switzerland) section 5.3.0.2