Grid, Conductors and Conductor Colours

🌐 Machine-translated page. The German version is authoritative.

From the power plant to the Steckdose (socket outlet)

Electricity is generated and distributed as Drehstrom (three-phase current): three alternating voltages shifted by 120° relative to each other. They arrive at the house via three Außenleiter (line conductors) L1, L2, L3, plus the Neutralleiter (neutral conductor) N and – for safety – the Schutzleiter (protective conductor) PE.

This gives you the two voltages of the house grid:

Between	Voltage	Name	Typical loads
L1 and N (or L2–N, L3–N)	230 V	Wechselstrom (single-phase AC), Strangspannung (phase-to-neutral voltage)	Steckdose (socket outlet), lighting, all plug-in household appliances
L1 and L2 (or L2–L3, L3–L1)	400 V	Drehstrom, Außenleiterspannung (line-to-line voltage)	Herd (cooker), Durchlauferhitzer (instantaneous water heater), Wallbox 11 kW, heat pump, motors

The frequency is 50 Hz all over Europe: the voltage changes direction 50 times per second. The “230 V” is the Effektivwert (RMS value); the peak value is about 325 V.

The five conductors and their colours

Since DIN VDE 0293-308 (2003), the colours have been standardised in Germany. You need to know them in your sleep – the colour decides whether an installation is safe.

Conductor	Abbreviation	Colour	Task
Außenleiter 1	L1	brown	carries voltage (“phase”)
Außenleiter 2	L2	black	carries voltage
Außenleiter 3	L3	grey	carries voltage
Neutralleiter	N	blue	return conductor, near 0 V against earth in normal operation
Schutzleiter	PE	green-yellow	carries no current in normal operation; conducts fault current to earth so that the protective device trips

Green-yellow is taboo for everything else. The Schutzleiter must never be used as an Außenleiter or Neutralleiter, and no other conductor may be green-yellow. Blue is reserved for the Neutralleiter; only if there is no N (for example in a switch wire) may blue be used differently – then the core must be marked at both ends. It’s cleaner not to do it at all.

Black and grey in a 3-core cable: if you see a cable with brown, black, grey in the bathroom, it’s a switch or Wechselschaltung (two-way switching) cable without N – brown is the incoming Außenleiter, black and grey are switched or corresponding.

Number of cores and assignment of common cables (NYM-J)

Cable	Cores	Use
NYM-J 3×1.5 mm²	brown, blue, green-yellow	Lighting (B10)
NYM-J 3×2.5 mm²	brown, blue, green-yellow	Steckdose (B16)
NYM-J 5×1.5 mm²	brown, black, grey, blue, green-yellow	Wechselschaltung with Steckdose, series switching
NYM-J 5×2.5 mm²	brown, black, grey, blue, green-yellow	Herd (3×B16, 400 V)
NYM-J 5×10 mm² / 5×16 mm²	as above	Zuleitung (incoming feeder) to the Unterverteilung (sub-distribution board), main feeder

The J means: with a green-yellow Schutzleiter. O (NYM-O) would have none – practically no longer used in residential construction.

Older installations

In installations from before 2003 you’ll find black, brown, black for the Außenleiter; before about 1965 the Schutzleiter was sometimes red and the Neutralleiter grey. In very old installations there is the klassische Nullung (classic neutralisation) without a separate PE. When working in old installations, the rule is: never rely on the colour, always measure.

Grid types: TN, TT, IT

The grid type describes how the star point of the transformer and the enclosures of the equipment are connected to earth. The letters (DIN VDE 0100-100):

First letter – star point of the grid: T = directly earthed (terre), I = isolated.
Second letter – bodies of the equipment: N = connected to the star point (via PE/PEN), T = own earth electrode.

Grid type	How	Where
TN-C	PE and N in one conductor (PEN) up to the consumer	old installations, main feeders, no longer permitted for new final circuits
TN-S	PE and N separate from the transformer onwards	industry, large installations
TN-C-S	PEN up to the house, split there into PE and N	standard in German residential buildings
TT	house has its own earth electrode, no PE connection to the grid	some rural grids, southern Germany, abroad
IT	grid not earthed, first fault only triggers an alert	operating theatres, emergency power supply

In the TN-C-S grid, the PEN conductor arrives at the Hausanschlusskasten (house connection box) and is split into PE and N on the Haupterdungsschiene (main earthing busbar). From there, the two must never be connected again – otherwise no RCD (residual current device) will work, and the Schutzleiter will carry operating current. That’s exactly why every RCD group in the Unterverteilung has its own N terminal.

Earthing and potential equalisation

The PE is only as good as the earth it is attached to. This is ensured by the Fundamenterder (foundation earth electrode, a steel strip in the foundation, mandatory for new buildings since 2007), the Haupterdungsschiene (HES) in the house connection room, and the Schutzpotentialausgleich (protective equipotential bonding): water pipes, heating, gas line, antenna mast, steel structures are connected to the HES so that in the event of a fault no voltage arises between two touchable metal parts.

In the bathroom, the zusätzlicher Schutzpotentialausgleich (supplementary equipotential bonding) is added (DIN VDE 0100-701): bathtub, pipes and the PE of the circuits are connected locally.

Test yourself

🧠 Test yourself

1. What colour does the Außenleiter L3 have?

2. What voltage is there between L1 and L2?

3. Which grid type is the standard in German residential buildings?

4. What applies to the colour green-yellow?

5. Why must PE and N never be connected again after the split?