3-Way Switch Wiring Diagram

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A full guide to wiring two 3-way switches that control one light from two locations, including traveller cable routing and troubleshooting for residential installations.

A 3-way switch circuit allows a single light fixture (or group of lights) to be switched independently from two different locations — a staircase top and bottom, either end of a hallway, or both sides of a large room. The arrangement uses two 3-way switch mechanisms, each of which has one common (COM) terminal and two traveller terminals (often labelled TRV1 and TRV2, or TRAV A and TRAV B). The common terminal on the first switch receives the incoming line conductor. The common terminal of the second switch feeds the switched line to the light. The two traveller terminals on switch 1 connect to the corresponding two traveller terminals on switch 2 via a pair of traveller conductors.

Regardless of the positions of both switches, the circuit works because one traveller is always completing a path from the first switch common through to the second switch common — the light is ON whenever both switches route through the same traveller. When either switch is toggled, it redirects its common to the other traveller, breaking the existing path and making the light change state.

In NEC-governed (North American) installations, the traveller cable is typically 3-wire (black, red, white) with a bare or green ground. Black and red are the two travellers; white is re-identified as the switch leg using a band of coloured tape at each termination. In UK/AU wiring, a 3-core-and-earth cable (brown, black, grey + green/yellow earth) simplifies identification: brown = line, black and grey = travellers.

Note: All wiring described here is generic in nature and applies to standard 3-way switch mechanisms. The wiring approach is consistent across major switch brands and ranges. Local code compliance and terminal capacity should always be verified against the specific switch manufacturer's datasheet and your jurisdiction's applicable wiring standard (NEC NFPA 70, BS 7671, IEC 60364, or AS/NZS 3000). Always have work inspected by a licensed electrician.

Eaton offers both standard toggle and decorator (paddle-style) 3-way switches, and both follow the same electrical wiring principle, but the physical terminal layout differs slightly between the two product families. The decorator-style switches have side-wired screw terminals recessed into the body rather than the traditional screws on the side ears, so it is important to check the label on each terminal (COM, T1, T2) rather than relying on colour alone. Eaton's included instruction sheet should always be consulted for the exact terminal arrangement of your specific model before connecting wires.

How to wire eaton 3 way switch diagram

Plan the cable route and identify switch locations Determine the positions of both switch boxes and the light fixture. Plan whether power feeds switch 1 or the light fixture first. A power-to-switch configuration routes line and neutral to switch 1, then a 3-wire traveller cable to switch 2, then a 2-wire cable from switch 2 to the light. A power-to-light configuration runs differently and requires re-identifying the white as a switched line.
Isolate and verify dead Switch off the MCB or breaker protecting the circuit. Use a non-contact voltage tester at each switch location and at the light fixture, followed by a proving unit, to confirm zero voltage before touching any conductors.
Run the cable Route 2-wire cable from the panel or junction box to switch box 1. Route 3-wire cable from switch box 1 to switch box 2. Route 2-wire cable from switch box 2 to the light fixture. Secure cables at intervals specified by your local code (typically every 1.2–1.5 m in NEC jurisdictions; every 400 mm in BS 7671 where not in conduit).
Wire switch 1 Connect the incoming line conductor to the COM (common) terminal — identified by a darker screw or 'COM' marking. Connect the two traveller conductors (black and red in NEC, or black and grey in BS 7671) to the two brass-coloured traveller terminals. Sleeve or tape re-identified white conductors used as a switch leg with black or red tape. Connect the protective earth to the ground terminal or bare to the grounding screw.
Wire switch 2 Connect the matching traveller conductors from switch 1 to the two traveller terminals of switch 2. Connect the switched line conductor going to the light to switch 2's COM terminal. This conductor completes the circuit to the light when both switches are aligned on the same traveller. Connect the protective earth to the ground terminal.
Wire the light fixture At the ceiling box or pendant, connect the incoming switched line conductor from switch 2's COM to the light's line (hot) terminal. Connect the neutral directly from the panel supply to the light's neutral terminal. Connect the ground to the fixture ground terminal and to the metal box. Do not switch the neutral.
Test operation Reinstate the breaker. Verify that toggling switch 1 changes the light state regardless of switch 2's position, and that toggling switch 2 changes the light state regardless of switch 1's position. If the light only works in one of the four possible switch combinations, a traveller is on the wrong terminal. Isolate and recheck.

Specifications

Switch type	3-way (SPDT) — one common, two traveller terminals
NEC current rating (typical residential)	15 A at 120/277 V AC
BS 7671 current rating (typical residential)	10 A at 250 V AC
Traveller cable type (NEC)	14/3 NM-B (3-wire with ground)
Traveller cable type (BS 7671)	3-core + earth, 1.0–1.5 mm² flat T&E or round cable
Applicable standards	NEC (NFPA 70) Article 404; BS 7671 Chapter 55; IEC 60364-5-55; AS/NZS 3000
Terminal identification (COM)	Black or dark-bronze screw; may be labelled COM or C
Terminal identification (travellers)	Brass-coloured screws; may be labelled TRV, TRAV, or 1/2

Safety warnings

Electrical work must comply with the wiring regulations applicable to your jurisdiction: NEC (NFPA 70) in the USA and Canada, BS 7671 in the UK, IEC 60364 internationally, or AS/NZS 3000 in Australia and New Zealand. In most jurisdictions this work requires a licensed or registered electrician.
Always isolate the circuit at the distribution board or consumer unit and verify zero voltage with a calibrated tester before touching any conductor. A non-contact tester alone is not sufficient — follow with a known-good proving unit.
Only the line conductor must be switched. Never install the switch mechanism in the neutral conductor — this leaves connected equipment at line potential even when the switch is in the OFF position.
Where 3-wire cable is used with a white conductor serving as a traveller or switch leg, re-identify it at every termination point with coloured tape or sleeving to indicate it carries line potential and is not a neutral.

Tools needed

Non-contact voltage tester (CAT III rated) and proving unit
Flat-blade and Phillips insulated screwdrivers
Wire strippers appropriate for cable gauge
Fish tape or cable draw wire (for concealed runs)
Continuity and insulation resistance tester
Drill and bits for cable routing
Stud finder (for timber-framed walls)
Multi-function tester or plug-in circuit analyser

Common mistakes

Connecting the traveller conductors to the common terminal and the line to a traveller terminal — the most common cause of a 3-way circuit that works in only one combination.
Using 2-wire cable between the two switches when 3-wire cable is required, forcing the installer to add a junction box or use a different wiring method.
Failing to re-identify white conductors used as travellers or switch legs, creating a code violation and future hazard for anyone working on the circuit.
Swapping the two switch boxes in the plan so switch 2 receives the line feed and switch 1 feeds the light — the circuit will still work, but the wiring at each box will be transposed.
Not securing the cable at the required intervals, allowing the cable to drop or sag in the wall cavity and creating mechanical stress at the terminations.

Troubleshooting

Light works in only one switch position combination: Cause: A traveller wire is connected to the common terminal of one switch instead of the correct traveller terminal. Fix: Isolate the circuit. At each switch, identify the COM terminal (dark-coloured screw). Verify that the feed and switched-line wires are on the COM terminals and that the two traveller wires occupy the two brass traveller screws. Swap if transposed.
Light is always ON regardless of switch positions: Cause: A traveller conductor is shorted to the line or to the switched line, bypassing the switching mechanism. Fix: Isolate. Disconnect the 3-wire traveller cable at both switch boxes. Perform an insulation resistance test at 500 V DC between each conductor pair. Locate and repair the fault — often a damaged cable where it passes through a stud or joist.
MCB trips when the circuit is energised: Cause: A short circuit between line and neutral or between line and earth, typically at one of the back boxes due to a stray conductor strand. Fix: Isolate. Disconnect all conductors at both switch boxes and the light fixture. Test insulation resistance from the panel. Reconnect one section at a time to isolate the fault location, checking for stray strands at each termination.

Frequently asked questions

What is the difference between the common terminal and the traveller terminals on a 3-way switch?

The common terminal is the single terminal that routes the incoming line (at switch 1) or the outgoing switched line (at switch 2) through the switch. The two traveller terminals are the two alternate paths the common bridges to when the switch is in each of its two positions. Swapping the common with a traveller will cause the light to behave incorrectly.

Can I use a 2-wire cable for a 3-way switch installation?

Only for the feed from the panel to switch 1 (line and neutral/ground). Between the two 3-way switches you need a minimum of a 3-wire cable to carry the two traveller conductors plus a protective earth. Using 2-wire cable between the switches is a common cause of incorrect wiring and code violations.

My 3-way switch works in one combination but not the other. What is wrong?

This is almost always a traveller wire incorrectly placed on the common terminal of one switch, rather than on a traveller terminal. Remove both switch plates, locate the common terminal on each switch (usually a different colour screw — dark or black — compared to the brass traveller screws), and verify each wire's position. Continuity-test the traveller pair separately.

Does it matter which traveller terminal I use for which traveller wire, as long as I am consistent?

No. The circuit operates symmetrically — traveller terminal 1 on switch 1 can connect to traveller terminal 1 or 2 on switch 2, provided the same conductor pair is used across both ends. However, a standard convention (black to brass, red to brass at both switches) makes future troubleshooting much faster.

Can a 3-way switch be used as a regular single-pole switch?

Yes. Connect the incoming line to the common terminal, the outgoing switched line to either traveller terminal, and leave the other traveller terminal unused. The switch then operates as a single-pole: it connects or disconnects the line at the common-to-traveller bridge. The unused traveller terminal must be left isolated, not connected to anything.

What is the wiring diagram for an Eaton 3-way decorator switch?

On an Eaton decorator 3-way switch, the common (COM) terminal is typically identified by a darker screw or a 'COM' label and connects to either the hot supply (at the first switch) or the switched-hot to the fixture (at the second switch). The remaining two terminals are the travellers and accept the two wires running between the pair of switches — polarity of the travellers does not matter. Wire the common and both travellers with the same gauge conductor (14 AWG for a 15 A circuit, 12 AWG for 20 A) and always confirm the terminal markings on the physical switch before energising.

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