2-Way Lighting Wiring Diagram: How to Wire Two Switches to One Light
This is a free printable 2 way lighting diagram: download the diagram as SVG or open it and print to paper or PDF.
A reference two-way switching wiring diagram showing how to control a single light from two switch positions, including strappers, common terminals, and cable requirements.
Two-way switching allows a single light fitting (or group of lights) to be controlled from two separate switch positions — the most common example being a staircase controlled from both the bottom and the top landing. The circuit is fundamentally different from a simple one-way switch circuit because each switch must be able to change the state of the other.
**How two-way switching works:** Each two-way switch has three terminals: - **L1:** first switched terminal - **L2:** second switched terminal - **COM (Common):** the terminal that connects to either L1 or L2 depending on switch position
The Live conductor from the distribution board feeds the COM terminal of switch 1. Two 'strapper' wires (the conductors that run between the two switches) connect L1 of switch 1 to L1 of switch 2, and L2 of switch 1 to L2 of switch 2. The COM terminal of switch 2 connects to the Live terminal of the light fitting. The Neutral from the distribution board connects directly to the Neutral terminal of the light fitting, bypassing both switches.
**Circuit operation:** In any given switch position, current flows through COM of switch 1 → to either L1 or L2 → through the strapper → to the COM of switch 2 → through to the lamp. Changing either switch redirects current to the other strapper wire — if the light was on, it turns off; if it was off, it turns on. Both switches can change the state of the lamp regardless of the current position of the other switch.
**UK three-plate wiring:** In older UK installations, the three-plate (ceiling rose) method joins Neutral and Earth at the ceiling rose, with switched live returning to the rose. In modern installations (post-17th Edition BS 7671), all conductors including Neutral should be available at the switch positions to comply with updated requirements for functional earth and switched circuits.
**Intermediate switching (3 switch positions):** When three switch positions control one light, an intermediate switch is inserted between the two two-way switches. The intermediate switch effectively crosses or un-crosses the two strapper wires, allowing any switch position to control the light.
How to wire 2 way lighting diagram
- Isolate all power at the consumer unit Switch off the lighting circuit MCB and verify dead at the light switch and light fitting with a non-contact voltage tester. Apply lockout to the MCB if there is any risk of accidental re-energisation during the installation.
- Plan the cable route between switch positions Determine the cable route from switch position 1 to switch position 2. Two-way switching requires 3-core-and-earth cable (four conductors including earth) for the strapper section. Measure the cable run length and add at least 15% for routing slack. Plan to minimise cable damage in walls and ceilings.
- Wire the supply at switch 1 (COM terminal) The Live supply conductor from the distribution circuit feeds the COM terminal of switch 1. In some installation methods, this is a switched live returning via the ceiling rose. In modern method (switch loop from consumer unit), the Live from the MCB reaches switch 1 first.
- Connect the strappers between the two switches Connect the first strapper wire from L1 of switch 1 to L1 of switch 2. Connect the second strapper from L2 of switch 1 to L2 of switch 2. Use 3-core-and-earth cable for this section: cores typically identified as brown, black (or grey), and blue — sleeve any repurposed-colour conductors with brown or blue sleeving to indicate their new function per BS 7671.
- Connect the light supply at switch 2 (COM terminal) The COM terminal of switch 2 provides the switched live to the light fitting. Run this conductor from the COM of switch 2 to the Live terminal of the light fitting. In older UK ceiling rose wiring, this is the 'switched live' returning to the rose.
- Connect Neutral and Earth to the light fitting The Neutral from the supply cable connects directly to the Neutral terminal of the light fitting — it does not pass through the switches. Connect the circuit earth to the Earth terminal of the light fitting, the back box earth terminal at each switch position, and the earth terminal at the ceiling rose or light fitting back plate.
- Test operation from both switch positions Restore power and test all four combinations: switch 1 up/switch 2 up (light on or off), switch 1 up/switch 2 down, switch 1 down/switch 2 up, switch 1 down/switch 2 down. Every toggle of either switch should change the light state. If the light is controlled only from one switch, the strappers are incorrectly connected or a COM terminal is miswired.
Specifications
| Switch rating | 10 A, 230 V (standard UK lighting switch) |
|---|---|
| Supply cable (lighting circuit) | 1.0 mm² twin-and-earth (6 A MCB) or 1.5 mm² (10 A MCB) |
| Strapper cable | 1.0 mm² 3-core-and-earth minimum |
| MCB rating (lighting circuit) | 6 A or 10 A (UK residential) |
| RCD protection | 30 mA required for circuits in high-risk zones per BS 7671 |
| Maximum lighting circuit load (UK, 1.0 mm²) | 1380 W at 230 V (6 A MCB) |
| Switch terminal identification | COM, L1, L2 (BS standard two-way switch) |
Safety warnings
- Lighting circuit wiring must be carried out by a qualified electrician in accordance with BS 7671 (UK), NEC/NFPA 70 (US), AS/NZS 3000, or IEC 60364 as applicable. In the UK, additions and alterations to fixed wiring in dwellings must comply with Part P of the Building Regulations.
- Always isolate the circuit at the consumer unit and verify zero voltage at all switch and light positions with a non-contact voltage tester before touching any conductors.
- Repurposed conductors used in non-standard colour-code roles must be sleeved or marked at each end to indicate their actual function, per BS 7671 regulations.
- Earth conductors must be connected at every accessory, back box, and fitting. A missing earth connection at any switch or fitting is a critical safety fault.
- This diagram is for reference and educational purposes only. Always comply with local electrical installation regulations.
Tools needed
- Non-contact voltage tester
- Multimeter (voltage, continuity)
- Wire strippers (suitable for 1.0–1.5 mm² conductors)
- Flat-blade and cross-head screwdrivers
- Earth sleeving applicator
- Cable fish tape or draw wire (for pulling cable through voids)
- Drilling equipment (if channelling or drilling for cable routes)
Common mistakes
- Connecting the supply Live to L1 or L2 instead of COM on switch 1 — the circuit will only work in one switch position.
- Using only one strapper wire between the two switches instead of two, making toggle operation impossible from both positions.
- Failing to connect the earth to the metal back box — a floating back box earth is a risk if a fault occurs inside the switch.
- Crossing the strapper connections (L1 to L2 and L2 to L1) — the circuit still works in this case, but it will be inconsistent with the standard wiring and difficult for future fault-finding.
- Not sleeving bare earth conductors inside accessories, leaving bare copper exposed adjacent to live terminals.
Troubleshooting
- Light is only controllable from one switch; the other switch has no effect
- Cause: One strapper wire is missing or disconnected, or a COM terminal is incorrectly connected as L1 or L2 Fix: Isolate the circuit. Test continuity of both strapper wires between the two switch positions. Verify that the COM terminal at each switch is identified correctly and connected per the wiring diagram. A missing strapper will show as an open circuit.
- Light is permanently on regardless of switch position
- Cause: Both strappers are bridged together inside the switch accessory, or supply Live is directly connected to the lamp without passing through the switch COM Fix: Isolate and inspect the switch wiring at both positions. Verify that only one conductor is connected to COM and that the strappers are separated between L1 and L2 on each switch.
- Light flickers or fails intermittently when switch is toggled
- Cause: Loose terminal connection at a switch or light fitting, or damaged strapper conductor with intermittent continuity Fix: Isolate and check all terminal connections at both switches and the light fitting. Test strapper wire continuity while flexing the cable — a fault will show as intermittent. Replace any damaged cable section.
Frequently asked questions
Why do I need two strapper wires between the two switches?
The two strapper wires are both potential current paths between the switches. At any given moment, current flows through only one of them (determined by switch positions), but the circuit needs both paths available so that either switch can redirect the current to the other path, changing the light state. Using only one wire between switches would create a single-state circuit with no second path.
Can I use standard 2-core cable for two-way switching?
No. Standard 2-core-and-earth cable has only one conductor for active current plus earth. Two-way switching requires three conductors between the two switch positions (the two strappers and either a common return or a switched live, depending on wiring method). Use 3-core-and-earth cable between the two switches, or two separate 2-core cables.
How do I identify the COM terminal on a two-way switch?
Most two-way switches are labelled COM, C, or L. The COM terminal is usually a different colour (often black or darker) or physically separated from the L1 and L2 terminals. Consult the switch manufacturer's wiring diagram. Connecting to the wrong terminal will result in the light only working from one switch position, or not working at all.
Can I convert an existing one-way switch circuit to two-way?
Only if you have or can install 3-core-and-earth cable between the two switch positions. If only a 2-core cable runs between the existing switch and the lamp, you must either run additional cable or replace the entire cable run. In most dwellings, pulling new cable through walls and ceilings is the main labour element of this job.
What is an intermediate switch and when do I need it?
An intermediate switch has four terminals and is used when you need to control one light from three or more positions (for example, a long corridor with switches at both ends and in the middle). It is inserted in the strapper cables between the two two-way switches. One intermediate switch per additional switch position beyond two is required.
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