How to wire a single-pole switch
Lucas Morel
Key Takeaways
- A single-pole switch only receives two wires: the phase and the lamp return.
- The standard does not mandate any specific color for the phase wire, but prohibits three.
- The green and yellow earth wire should never be connected to a single-pole switch.
- Turn off the circuit breaker, then verify the absence of voltage. Color alone is not enough.
Connecting a single-pole switch requires two wires: the phase coming from the electrical panel, and the lamp return going back to the light fixture. The order does not matter; the two terminals are interchangeable on a single-pole mechanism.
This is the most accessible electrical connection for homeowners, yet it's also where the most misconceptions are found. No, the phase is not necessarily red. No, the green and yellow wire should not be connected. No, the color of a wire is not enough to identify it in an old installation. Here you will find the complete wiring diagram, the necessary equipment, the electrical safety procedure, and what the standard actually says about colors.
Which Wires for a Single-Pole Switch
A single-pole switch cuts the circuit on the phase conductor. It therefore receives two wires, and only two.
Wire 1, the phase: comes from the electrical panel, supplies current.
Wire 2, the lamp return: goes back to the light fixture.
The neutral: does not pass through the switch; it goes directly from the panel to the light fixture.
The earth: is never connected to a single-pole switch.
If you find a green and yellow wire in the flush-mounted box, do not cut it or connect it to the mechanism. It is intended for the light fixture and must remain isolated in the box, folded and protected. Removing it complicates any future work on the light fixture, and it's irreversible without reopening the chase.
The Color Code, and What the Standard Really Says
This is the point that most guides oversimplify. NF C 15-100 standard only mandates a color for two conductors, and it merely prohibits certain colors for the third.
| Conductor | Color | Status |
|---|---|---|
| Neutral | Light blue | Mandatory, reserved |
| Earth, protective conductor | Two-tone green and yellow | Mandatory, reserved |
| Phase | Any color except light blue, green alone, yellow alone, and green-yellow | No specific color mandated |
Promotelec clearly states in its FAQ: the neutral must always be blue, the earth green and yellow, and the phase conductor can be any color with the exception of those reserved. Red is a common practice, not an obligation. You will find brown, black, grey, orange, or purple, all perfectly compliant.
For lamp returns, electricians often use orange or purple to distinguish them from a direct phase. This is a trade convention, not a rule.
Before 1970, Everything Changes
In installations prior to the generalization of the standard, colors are often inconsistent, and the neutral may have been red. Color is then only an indication. It never replaces a verification with a voltage tester or multimeter, regardless of the age of the dwelling.
Equipment Needed for Connection
Five tools are sufficient for the connection, and the first one is non-negotiable.
- A voltage tester or a multimeter. The neon screwdriver tester gives an indication, not a certainty.
- An insulated flat-head screwdriver of 2.5 or 3 mm for screw terminals.
- Wire strippers, set to the conductor's gauge.
- Wire cutters to neatly trim a damaged end.
- A Phillips screwdriver for claws or mechanism fixing screws.
Also, have some electrician's tape to mark the conductors before disconnecting them. This avoids having to figure out which wire went where, once the old mechanism has been removed.
Single, double, two-way, or dimmer: our four collections offer each function in the same shades, to equip an entire home without visual breaks from one room to another.
See wall switchesThe Flush-Mounted Box and Power Supply Routing
Before any connection, a word about what's behind the mechanism. The flush-mounted box receives the conductors that arrive through a conduit from a junction box, which is itself connected to the electrical panel.
Standard box diameter: 67 mm.
Minimum depth: 40 mm for a simple mechanism, 50 mm for a dimmer or a connected module.
Conductor cross-section for lighting: 1.5 mm² under a 16 A circuit breaker.
ICTA conduit: 16 or 20 mm diameter depending on the number of conductors.
Box depth is the renovation pitfall. Older models are sometimes 30 mm where a current mechanism requires 40 mm. You only discover this when trying to fit it in, after the mechanism is already connected. Measure before ordering.
When no box exists and the wall cannot be channeled, surface mounting remains the solution. The mechanism is then placed in a surface-mounted box fixed to the partition, with visible cable routing in trunking or conduit.
How to Verify the Absence of Voltage
This is the step that no one should skip, and it takes thirty seconds.
- Turn off the circuit breaker for the affected circuit at the electrical panel, not just the switch. An open switch leaves the phase present on one of the two terminals.
- Tag the panel, with adhesive tape or a note, so that no one switches it back on while you are working.
- Test your tester on a known live source to confirm it is working.
- Check each conductor in the box, one by one, against the earth.
- Retest the tester on the known live source, to be sure it hasn't failed in the meantime.
This double verification before and after seems excessive. It is the standard procedure for electricians in terms of electrical safety, and it exists because a faulty tester indicates exactly the same thing as a de-energized circuit.
If you take the opportunity to move the control point, first check the permitted installation height. It is detailed in our guide on the height of switches and sockets.
How to Wire a Single-Pole Switch, Step by Step
Replacing an existing mechanism takes fifteen minutes. Creating a new control point requires pulling a new line, which is another project.
- Cut and verify according to the procedure above.
- Remove the cover plate; it clips or unscrews depending on the model.
- Remove the mechanism from the flush-mounted box by loosening the claws or screws.
- Mark the two conductors with adhesive tape before disconnecting them, even if they seem obvious to you.
- Disconnect. For an automatic terminal, press the release button. For a screw terminal, loosen it.
- Recut and restrip the ends by 8 to 10 mm if the copper is damaged or blackened.
- Connect the new mechanism. The two terminals of a single-pole switch are interchangeable; the order does not matter.
- Check that no bare copper protrudes from the terminal, and gently pull each wire to check its hold.
- Insert into the box, tighten the claws or screw, check for alignment.
- Clip on the plate, reset the circuit breaker, test.
Stripping Length
8 to 10 mm, no more. Too short, the contact is poor and the terminal heats up. Too long, bare copper protrudes from the terminal and creates a risk of contact with the mechanism or with the other conductor. Most mechanisms have a stripping template molded on their back, use it.
Once the mechanism is connected, the final check involves two actions: gently pulling each wire to verify its hold in the terminal, and ensuring that no bare copper protrudes before fitting it into the box.
The Electrical Diagram of a Single-Pole Switch
The simplest lighting circuit consists of three elements and four conductors in total.
From the panel, the phase goes to the switch. It enters one terminal, exits through the other as the lamp return, and reaches the light fixture. The neutral goes directly from the panel to the light fixture, without passing through the switch. The earth follows the same path as the neutral, from the panel to the light fixture, also bypassing the switch.
When the switch is closed, the circuit is complete and the lamp turns on. When it is open, the phase is interrupted and the light fixture is no longer powered.
| Path | Conductor | Passes through the switch |
|---|---|---|
| Panel to switch | Phase | Yes, input terminal |
| Switch to light fixture | Lamp return | Yes, output terminal |
| Panel to light fixture | Neutral | No |
| Panel to light fixture | Earth | No |
To draw your own wiring diagram before starting work, note on a piece of paper what you see in the box: number of wires, colors, and where they go if you can deduce it. Photograph the existing setup before disconnecting; it's the most effective backup.
This wiring principle remains valid regardless of the chosen mechanism. A double-pole switch connection uses the same diagram with an additional return, a two-way switch replaces the return with two travelers.
Other Types of Switches, and Their Number of Wires
The single-pole switch is the only one that receives only two wires. If you find three or more, you are not dealing with a simple switch.
| Type | Number of wires | Function |
|---|---|---|
| Single-pole switch | 2 | One light point controlled from a single location |
| Two-way switch | 3 | One light point controlled from two locations, two travelers plus phase or return |
| Double-pole switch | 3 | Two independent circuits, one phase and two returns |
| Push button | 2 | Pulse to a latching relay or timer |
| Dimmer | 2 | Like a single-pole, with a mandatory compatible bulb |
A two-way switch mechanism has three terminals, often marked L, 1, and 2. Terminal L receives the phase or return, terminals 1 and 2 receive the travelers. You cannot replace a two-way switch with a single-pole switch without modifying the wiring. The complete wiring of this setup is detailed in our guide on how to wire a two-way switch.
Can an Electrician Be Dispensed With for Switch Wiring?
Replacing an existing mechanism is within the reach of a careful individual, provided three conditions are met.
- You are not modifying the wiring; you are replacing one mechanism with another of the same function.
- You have a voltage tester and know how to use it.
- The installation complies with current standards, with a residual current device and consistent colors.
Call an electrician if you need to run a new line, if you find inconsistent colors, if the box is too shallow for the mechanism, or if the installation dates from before 1970 and has not been updated. In the latter case, replacing a switch is often an opportunity to discover a broader defect.
Work on a bathroom light point also adheres to specific rules related to protection zones, detailed in our guide on IP ratings and wet area zones.
Frequently Asked Questions
How to wire a single-pole switch?
Turn off the circuit breaker, verify the absence of voltage, remove the cover plate, and take out the mechanism. Mark the two conductors, disconnect them, then connect them to the new mechanism. The two terminals of a single-pole switch are interchangeable; the order does not matter.
Which wires for a single-pole switch?
Only two wires: the phase coming from the panel and the lamp return going back to the light fixture. The neutral and earth do not pass through the switch; they go directly from the panel to the light point.
What are the steps to install a switch?
Turn off and verify the absence of voltage, remove the cover plate, take out the mechanism, mark the wires with tape, disconnect, re-strip by 8 to 10 mm if necessary, connect, check that no bare copper protrudes, fit in and clip the plate.
How to verify the absence of voltage?
Turn off the circuit breaker, test your tester on a known live source, check each conductor in the box against the earth, then retest the tester on the known source. A faulty device indicates the same thing as a de-energized circuit.
What tools are needed to wire a switch?
A voltage tester or multimeter, an insulated flat-head screwdriver of 2.5 or 3 mm, wire strippers, wire cutters, and a Phillips screwdriver. Add electrician's tape to mark the conductors before disconnecting.
What color for the phase wire?
No specific color is mandated. The standard reserves light blue for the neutral and green-yellow for the earth, and prohibits these colors for the phase, as well as green alone and yellow alone. Red is a common practice, not an obligation.
How to create a wiring diagram?
Note the number of wires present in the box, their color, and their destination if you can deduce it. Photograph the existing setup before disconnecting. For a single-pole switch, the diagram consists of two wires: phase in, lamp return out.
How to install a switch without an electrician?
This is possible for a simple replacement if you are not modifying the wiring, if you have a voltage tester, and if the installation complies with current standards. Call a professional to run a new line or if you encounter inconsistent colors.
What cable cross-section for a lighting circuit?
1.5 mm² under a 16 A circuit breaker is the standard cross-section for domestic lighting. Conductors run in an ICTA conduit of 16 or 20 mm from a junction box. The cross-section is not chosen during wiring; it is determined by the circuit.
Can a surface-mounted switch be wired?
Yes, when no flush-mounted box exists and the wall cannot be channeled. The mechanism is then placed in a surface-mounted box fixed to the partition, with visible cable routing in trunking or conduit. The connection remains the same.
Conclusion
Before unscrewing anything, take a picture of the existing setup with your phone. This is the most cost-effective step of the entire operation: thirty seconds, and you have an exact record of what you need to put back. The only question that remains is: how many wires do you actually see in that box?
Freelance writer, he writes the technical guides for the Aeraly blog and follows developments in the NF C 15-100 standard applied to housing.
August 2026
