Neutral wire

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 in the low- voltage network.

Identification and execution

The neutral line is referred to with the letter N, and in only the blue color ( past light blue, in Switzerland and 1989, yellow) over the entire length. The very common in Europe Schuko type CEE 7/4 has a symmetrical shape and does not distinguish the two current-carrying conductor outer conductor and the neutral conductor. A grounding devices connected exclusively via the protective conductor ( PE). Contrary to many opinions, there is no specific standard, or which specifies the position of the neutral conductor "left", " right", when horizontally arranged receptacles for CEE-7/4-Steckdose.

Basics

As defined in DIN VDE 0100-200 (Section 826-12-08 ) the neutral is a live conductor as well as the outer conductor and intended to carry current during normal operation. In consumer systems based on TN -C and TN -CS systems, the neutral conductor is considered suitable low impedance grounded when in any case, the respective permissible touch voltage between the neutral conductor and protective conductor is exceeded, it therefore "needs" not be (together with the outer conductors ) separated.

In the three- phase AC power supply, the current picks up in the neutral conductor, when currents of the same amperage, the same phase angle and without harmonic content flow in all three phase conductors. With unequal currents in the external conductors in the neutral conductor current flows, which compensates for the asymmetry and reaches the stream of the most heavily loaded phase conductor maximum under the above conditions. At different phases of the currents in the phase conductors, or at harmonics (especially the 3rd order ) in addition to the fundamental frequency of the current in the neutral conductor can exceed the power of the most heavily loaded phase conductor shall prevail.

Historical development

In the old VDE regulations, there was no neutral conductor. The principle of zeroing has been applied yet in 1958 only. The grounded conductor medium was designated as neutral and he had united the function of the protective conductor and the neutral conductor in itself, that corresponded in function to today's PEN conductor and was marked with the color light gray.

Since 1965 there is the concept center conductor functionally equivalent to today's neutral for the first time and was wired in Light Blue. At the same time the green / yellow marking for the protective conductor was introduced and the then permissible neutral was changed in color from light gray to green / yellow ..

In 1973, the so-called "classical zeroing " was suppressed and in June 1975, the neutral binding was renamed PEN.

The wire colors from 1965 to 2003 remained unchanged and the current wire color blue ( instead of light blue) for the neutral was introduced with the DIN VDE 0293-308:2003-01. Classic PEN systems can be found in customer installations in Germany which were completed before 31 March 1974, according to current standards only in the distribution network, the network operator and for special applications. The division of PEN in PE and N conductor is nowadays directly at the transfer by the network operator in the customer system in the entrance box. The term " neutral " was first mentioned in 1983 in the VDE.

The neutral conductor is also still often referred to incorrectly as neutral and falsely indicated as former wire color also "gray ", but it is in both cases around a conductor which today meets the PEN conductor.

Neutral interruption

In a polyphase network, such as a three-phase AC power supply, form in the event of an interruption of the neutral conductor ( " neutral tear " ), the resistances of consumables to the various phase conductors of a voltage divider, whereby the potential of the now "free" or "floating" neutral point at can move asymmetrical loading of the outer conductor. This uneven load distribution is called the unbalanced load. Thus, in highly unequal currents in the external conductors, virtually increase the tension between the loaded lowest phase conductor and the neutral point on the voltage between two phase conductors. This can lead to overvoltage damage.

According to current standards, the neutral conductor need not be switched. The neutral conductor must be connected ( terminals marked with N ) but under no circumstances alone but always together with all active conductors of a circuit and only with standard-compliant devices. A circuit related to the neutral conductor is excluded.

Special

In contrast to the currents of the fundamental frequency, the currents of the divisible by three harmonics in the neutral conductor do not cancel, but add up. This applies in the normal European mains frequency of 50 Hz in particular the third harmonic at 150 Hz and the ninth harmonic at 450 Hz - play even-numbered harmonics, no DC component is present, do not matter. There is the risk that in systems with multiple devices, which no or insufficient power factor correction have, such as switching power supplies is, for example, personal computers, TVs or fluorescent lamps with electronic ballasts, the neutral current is above the permissible limits, while the individual phase conductors their maximum current to which the hedge is dimensioned have not yet been reached. Newer standards take this into account and include load tables for common reference routing types with columns for different harmonic contents of the third harmonic of the phase currents.

Of in accordance with national standards, no single-pole switching devices may be used in the neutral conductor, or have single-pole change-over switch in the ( same ) be connected to the outer conductor (which is impossible to use in the neutral conductor ).

Standardize

• DIN VDE 0100-100:2009-06; Erection of low -voltage systems - Part 1: General principles, rules of general characteristics, definitions.
• DIN VDE 0100-200:2006-06; Erection of low- voltage systems - Part 200: Definitions.
• DIN VDE 0100-510:2011-03; Erection of low -voltage electrical installations - Part 5-51: Selection and erection of electrical equipment - General requirements.
• DIN VDE 0293-308:2003-01; Identification of the cores of cables / wires and flexible wires by colors.