Two-Way Switching, Single Switching and Socket Outlets

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

The three basic circuits

Almost every residential installation consists of three building blocks that you wire in your first year of Ausbildung (apprenticeship) until you can do them in your sleep:

Schaltung (circuit)	Task	Switches	Cores to the luminaire
Ausschaltung (single switching)	switch one luminaire from one location	1 Ausschalter (2 terminals: L, switched conductor)	L (switched), N, PE
Wechselschaltung (two-way switching)	switch one luminaire from two locations (hallway, bedroom)	2 Wechselschalter (3 terminals each: L, two corresponding)	as above; between the switches 2 corresponding conductors
Steckdose (socket outlet)	connecting portable devices	none	L, N, PE

For three or more switching locations, the Kreuzschaltung (intermediate switching) is added (one Kreuzschalter between two Wechselschalter) – its own guide follows.

Ausschaltung

The simplest circuit. The Außenleiter (line conductor) L (brown) goes to the switch, from the switch the geschalteter Leiter (switched conductor, black) goes to the luminaire, and from the luminaire the N (blue) returns directly. PE (green-yellow) goes to the luminaire if it has a Schutzleiter (protective conductor) connection – and always to the socket outlet.

Rule number one of installation: You always switch the Außenleiter, never the N. If the N (Neutralleiter, neutral conductor) is switched, the lamp still lights up, but it remains live when “off” – deadly when changing the lamp.

Cables: NYM-J 3×1,5 mm² from the Verteilerdose (junction box) to the switch (brown = L going, black = switched returning, run PE along, blue stays unused and insulated or is used as N for a Steckdose next to the switch) and 3×1,5 mm² to the luminaire.

Wechselschaltung

Vereinfachter Stromlaufplan. Beide Stromkreise hängen hinter LS-Schalter und RCD (30 mA), hier nicht gezeichnet.

Two Wechselschalter (two-way switches) each have three terminals: L (common contact, often marked with an arrow) and two outputs. The switch connects L to either one output or the other.

Switch 1: L (brown) onto the terminal L. The two outputs go as korrespondierende Leiter (corresponding conductors, black and grey) to switch 2.
Switch 2: corresponding conductors onto the two outputs. From the terminal L, the geschalteter Leiter (black) goes to the luminaire.
Luminaire: switched conductor, N, PE.

No matter the position: each flip of a switch always changes the state. If both switches are on the same corresponding conductor, the circuit is closed – light on.

Cables: NYM-J 5×1,5 mm² between the switches (brown L, black and grey corresponding, blue N for a Steckdose, PE) or 3×1,5 mm² if there is no Steckdose at the switch.

Check the terminal L on the switch with a continuity tester before you clamp – manufacturers mark it differently. If you swap L and a corresponding connection, the circuit only works in one position.

Steckdose (Schuko, Schutzerdungskontakt)

The Schuko-Steckdose (Schuko socket outlet) has three terminals: L, N and PE (Schutzkontakt, protective contact – the two clips). In Germany, the Steckdose is not polarity-safe – L can be on the left or the right. Common practice (not a standard) is N left, L right when looking at the outlet.

Rules:

Always connect PE – even if the device only has two poles. A Steckdose without PE is a defect.
Every Steckdose in the apartment behind an RCD 30 mA (DIN VDE 0100-410).
B16 with 2,5 mm². 1,5 mm² with B16 only for a short cable run (up to about 15 m when installed under plaster) – your Berufsschule (vocational school) will do the exact calculations.
Steckklemmen (push-in terminals) on modern Steckdosen: strip the core 10–12 mm, push it straight in, do a Zugprobe (pull test). With screw terminals: torque according to the manufacturer’s specifications.
Steckdosen in the bathroom: observe the Schutzbereiche (protective zones) according to DIN VDE 0100-701 – 60 cm distance from the bathtub / shower.
Mindestausstattung (minimum equipment) according to DIN 18015-2: for example, living rooms up to 20 m² need at least 5 Steckdosen, kitchens at least 7 (3 of them above the worktop). If you plan too few, everything later hangs off power strips.

Wiring step by step (practice wall or apartment)

Fünf Sicherheitsregeln (five safety rules). LS (Leitungsschutzschalter, miniature circuit breaker) off, locking device, verify absence of voltage at the Verteilerdose and all outlet boxes with a two-pole tester.
Read the plan. Stromlaufplan (circuit diagram) in aufgelöster Darstellung (schematic representation, functional relationships) and Installationsplan (installation plan, where everything sits). Tick off cores and terminals on the plan before you clamp.
Pull in the cables. From the Verteilerdose in a star pattern: to switch 1, switch 2, luminaire, Steckdose. Cut the cable with 15–20 cm of slack in every box. Cable routing in Installationszonen (installation zones, horizontal 30 cm below the ceiling or above the floor, vertical 15 cm next to doors and corners).
Strip the sheath and the cores. Strip the sheath without nicking the cores, strip the cores 10–12 mm (observe the terminal specification). Do not damage any copper strands.
Wire the Verteilerdose. With Verbindungsklemmen (connector terminals, Wago 221 or push-in terminals): all N together, all PE together, L onto the outgoing L conductor to switch 1, connect the corresponding conductors through, switched conductor to the luminaire. No conductor may be left loose in the box.
Connect the switch and Steckdose. Terminals according to the printed markings. Confirm L on the Wechselschalter with a continuity tester. PE on the Steckdose first.
Connect the luminaire. Switched conductor onto L of the luminaire, N onto N, PE onto PE. Even with Schutzklasse-II (protection class II) luminaires, keep PE available in the box (insulate it).
Test before switching on. See the next section.
Switch on and check the function. Test the Wechselschaltung from all four combinations. Check the Steckdose with a socket tester.
Label. Enter the Stromkreis (circuit) in the Verteiler (distribution board).

Testing according to DIN VDE 0100-600

Even the smallest circuit is tested and documented:

Besichtigen (visual inspection): colours correct, PE everywhere, no damaged cores, boxes closed, covers in place.
Durchgängigkeit des Schutzleiters (continuity of the protective conductor): from the PE terminal in the Verteiler to the Schutzkontakt of the Steckdose and to the PE of the luminaire, low impedance (typically below 1 Ω).
Isolationswiderstand (insulation resistance): all conductors against PE, 500 V DC, at least 1 MΩ. Disconnect or remove lamps and devices beforehand.
Schleifenimpedanz (loop impedance) at the Steckdose: the LS must trip in the event of a short circuit (B16: short-circuit current at least 80 A).
RCD test: tripping time and tripping current at the Steckdose.
Drehfeld (phase rotation) does not apply at 230 V.

Common mistakes

N switched instead of L. Works, but is deadly.
L and a corresponding connection swapped on the Wechselschalter. The circuit only works “sometimes”.
PE not connected or used as L in the box.
Blue core as the switched conductor without marking.
Core stripped too short – the terminal grips the insulation: loose connection, heat.
Core stripped too long – bare copper outside the terminal: risk of contact, short circuit.

Test yourself

🧠 Test yourself

1. Which conductor is switched in an Ausschaltung?

2. How many terminals does a Wechselschalter have?

3. What are the two conductors between two Wechselschalter called?

4. Which cable is installed for a Wechselschaltung with a Steckdose at the switch?

5. What is the minimum required insulation resistance?