Two switches, one light and a client who wants it on a schedule. On a 3-way circuit the old switches and the new devices work in different ways. This guide explains how to wire a 3 way smart switch in principle: what the circuit is, how the conductors are identified, the two common approaches and the safety steps. The wiring diagram itself always comes from the device’s own instructions.
How do you wire a 3 way smart switch?
With the breaker off and the circuit tested dead, the smart switch usually goes in the box where line enters, connected to line, load, neutral and ground. The other location gets the matching companion unit, often using one old traveler for its signal, or a wireless remote. Follow the device’s own diagram, and use a licensed electrician where local code requires one.
What a 3-way switch circuit is
A 3-way circuit controls one light, or one group of lights, from two locations. Each mechanical 3-way switch has three terminals: a common, usually the darker screw, and two traveler terminals. The common at one switch connects to line, the hot from the panel; the common at the other connects to load, the wire to the light.
Between the two switches run two travelers. Each switch connects its common to one traveler or the other, and the light is on when both switches pick the same traveler. Flipping either switch changes the path. The neutral does not pass through the switches; it runs to the light.
Layouts vary. Power can arrive at the first switch, at the light, or at the second switch, and in some homes the light sits between the two switch boxes. That decides which conductors are in each box.
Safety first: breaker off, tested dead
This is line-voltage work. It follows local code, may need a permit and in many jurisdictions requires a licensed electrician. If you are not qualified, stop here and hire one.
For workplaces, OSHA’s 29 CFR 1910.333 requires circuits to be disconnected from every energy source before work, and a qualified person to verify with test equipment that the parts are deenergized, including checking for voltage backfed from another source. The same habits apply on any job:
- Switch the breaker off. A wall switch is not a disconnect.
- Lock or tag the panel so no one turns it back on.
- Test your tester on a known live source, then test every conductor in both boxes, then test the tester again.
- Expect more than one circuit. A multi-gang box can hold conductors fed from different breakers.
3 way switch traveler, common, line and load: identifying each
Before removing anything, photograph each box and tag every conductor by the terminal it is on.
- Travelers: the two conductors on the matching traveler screws, the same pair in both boxes. Colors vary, so trust the terminals and your tags, not the insulation.
- Common: the conductor on the darker screw. In one box it is line, in the other it is load.
- Line or load: telling which common is line means a voltage measurement on an energized circuit. That is a job for a qualified person with the right meter and protective equipment. If no one on site is qualified, have an electrician identify it.
- Neutral and ground: note whether each box has a neutral bundle and a bare or green ground.
Watch for a white conductor taped or marked as a hot. In older layouts it is often re-identified that way, and it is not a neutral.
Two ways to make a 3-way circuit smart
Most smart 3-way setups replace the two mechanical switches with one smart switch and a second device that tells it what to do.
- Smart switch with companion switch: a matching companion, also called an accessory or remote unit, mounts in the second box. In many designs one old traveler carries its signal to the smart switch and the other is capped, but the instructions decide.
- Smart switch with a wireless remote: a battery remote mounts on the wall at the second location and talks to the smart switch by radio. The second box no longer switches anything, and its conductors are terminated as the instructions direct.
| Factor | Wired companion | Wireless remote |
|---|---|---|
| Second location | Wired into the old switch box | Mounted on the wall, no line connection |
| Uses the travelers | Usually one, for signal | No; conductors terminated per instructions |
| Neutral at the second box | Depends on the model | Not needed |
| Battery | None | Needs replacing |
| Matching rule | Same maker and series as the smart switch | Paired to the smart switch it controls |
A smart switch rarely works with the old mechanical 3-way switch at the other end. A few models are designed for it; most are not, so check the spec sheet.
How to wire a 3 way smart switch: the sequence
The logic most installs share is below; the connections always come from the device’s own diagram.
- Confirm the circuit is dead, as above, and keep the breaker locked off.
- Choose the box for the smart switch. Many models need it where line enters, with a neutral present; the instructions say which positions they allow.
- Match each tagged conductor to the terminal the diagram names: line, load, traveler, neutral and ground.
- Fit the companion, or remove the second switch and terminate its conductors as instructed.
- Check the device’s load rating against the lights, then restore power and test from both locations.
Brightness control raises its own questions about lamps and minimum load; our comparison of smart dimmer vs smart switch covers them.
The neutral, and why the ground is never a substitute
Most smart switches need a neutral to stay powered, and on a 3-way circuit it is often present in one box and missing from the other. Whether a box has one, and the options when it does not, are covered in our guide to the smart switch neutral wire.
Never connect a device’s neutral lead to the ground. The equipment grounding conductor is there to carry fault current back to the panel so the breaker trips. Using it as a neutral puts everyday current on that safety path and on the metal parts bonded to it. If there is no neutral where you need it, choose a device that does not need one or have an electrician add it.
Testing and 4-way circuits
With power back on, test the light from the smart switch, from the companion or remote, and from the app or hub. If the companion does nothing, turn the breaker off again and recheck its connection against the diagram.
A circuit with three or more switch locations adds 4-way switches in the middle. With a smart setup, each extra location usually gets another companion or remote. The radio decides which hub can control the smart switch; see Z-Wave vs Zigbee for lighting control and our tips on how to extend Z-Wave range.
Where to find multi-location lighting controls
The smart lighting controls category lists multi-location dimmers and remote switch and remote dimmer units, and the Z-Wave category lists automation devices, both in the security, surveillance and control division.
For pricing and availability, ask your sales representative through the Bursma contact page, or open a Bursma dealer account.
Frequently asked questions
Do you need two smart switches for a 3-way circuit?
Usually not. Most setups use one smart switch at the location the instructions allow, with a matching companion or a wireless remote at the other location.
Can I use a smart switch with my existing 3-way switch?
Only if the smart switch is designed for it. Most models need their own companion or remote, and a mismatched mechanical switch can stop the circuit working.
What happens to the traveler wires?
With a wired companion, one traveler often carries the signal and the other is capped. With a wireless remote, the conductors in the second box are terminated as the instructions direct. Never guess; follow the diagram.
Do I need an electrician to install a smart 3-way switch?
It depends on local code. Line-voltage work may need a permit and, in many places, a licensed electrician. Identifying line and load on a live circuit is qualified work.