3 Way Switch Diagram — Complete Wiring Guide
This is a free printable 3 way switch diagram: download the diagram as SVG or open it and print to paper or PDF.
A 3-way switch diagram shows how two switches work together to control one light from two separate locations — the top and bottom of a staircase, both ends of a hallway, or either side of a large room. Each 3-way switch has a common terminal and two traveler terminals. Correct wiring of the travelers and the common determines whether the circuit works at all. This guide walks through every wire, terminal, and connection.
Diagram checks and scope
- Components
- 6
- Wired connections
- 7
- Automated check
- Automated pin, route, source, and topology checks passed; this is not a safety certification.
A 3-way switch differs from a single-pole switch in a fundamental way: instead of simply opening or closing the hot wire, a 3-way switch connects its common terminal to one of two traveler terminals depending on switch position. Two 3-way switches are used together — when both commons connect through the same traveler wire, the circuit is complete and the light energizes. When each common connects to a different traveler wire (one to traveler 1, the other to traveler 2), the circuit is open and the light is off. The common terminal is usually identified by a black or darker screw on the switch body. The two traveler terminals are brass-colored screws. Never use white wires on the common terminal in standard installations — white must be neutral, and the common carries the hot signal. In the most common "power at switch 1" wiring configuration: the panel hot connects to the common of Switch 1. Two traveler wires (usually red and black in a 14-3 or 12-3 cable) connect the traveler terminals of Switch 1 to the traveler terminals of Switch 2. The common of Switch 2 connects to the fixture hot. The neutral runs directly from the panel through the circuit to the fixture. In "power at fixture" configuration, the cable routing changes but the switch connections remain the same — always hot to common of the first switch, travelers between switches, common of second switch to fixture. 4-way switches can be inserted between two 3-way switches to add additional control locations for long hallways or large rooms — each 4-way switch reverses the traveler pair using internal crossbar contacts.
How to wire 3 way switch diagram
- Run correct cable Between the two switch boxes, run 14-3 NM cable (or 12-3 for 20A circuits) — this provides black, white, red, and bare copper. The black and red serve as the two traveler wires; the white becomes the common hot from switch 2 to fixture (mark with black tape).
- Wire Switch 1 (power source side) Connect the incoming hot (black from panel) to the COMMON (dark) screw. Connect one traveler (black) to one brass screw and the second traveler (red) to the other brass screw. Connect ground to green screw.
- Wire Switch 2 (fixture side) Connect the switched hot going to the fixture (white wire marked with black tape) to the COMMON (dark) screw. Connect travelers (black and red from between switches) to the two brass traveler screws. Connect ground to green screw.
- Wire the fixture Connect the switched hot (from Switch 2 common) to the fixture hot terminal. Connect the neutral from the panel to the fixture neutral terminal. Connect grounds throughout.
- Test operation Restore power. Verify the light can be turned on and off from either switch independently. Test all four combinations: both up, both down, S1 up S2 down, S1 down S2 up — two combinations should be ON and two OFF.
Specifications
| Cable type | 14-3 NM (black, white, red + ground) |
|---|---|
| Switch type | 3-way (single-pole double-throw) |
| Common terminal | Dark (black) screw |
| Traveler terminals | Two brass screws on same side |
Safety warnings
- Identify the common terminal (dark screw) on each 3-way switch before connecting — connecting travelers to the common causes incorrect operation and potential arcing.
- Use 14-3 or 12-3 cable (three conductors plus ground) between the two switch boxes for the traveler wires — 14-2 cable does not have enough conductors for a proper 3-way circuit.
- De-energize the breaker and test all wires for voltage before touching — in a 3-way circuit, the travelers may carry voltage from the other switch even when the light appears off.
Tools needed
- Non-contact voltage tester
- Wire stripper (14 AWG and 12 AWG)
- Flathead and Phillips screwdrivers
- Needle-nose pliers for wire loops
Common mistakes
- Connecting the hot wire to a traveler terminal instead of the common terminal — the switch will operate the light in some positions but not others, depending on traveler pairing.
- Using two-conductor cable between switches — 14-2 lacks the second traveler wire, making proper 3-way wiring impossible without running additional wire.
- Connecting travelers crossed (Switch 1 traveler 1 to Switch 2 traveler 2) — the light controls are inverted but function correctly; however, this violates standard practice and confuses future electricians.
Troubleshooting
- Light stays on regardless of switch position
- Cause: Common terminal of one switch is connected to neutral instead of hot, creating a permanent return path Fix: De-energize, check which wire is on the common of each switch. The common of switch 1 must be the incoming hot (live at all times). If neutral is on the common, swap it to the correct position.
- Light controlled correctly only from Switch 1
- Cause: Switch 2 common terminal connected to a traveler terminal — the common position is incorrect Fix: At Switch 2, identify the dark screw (common). Ensure the wire going to the fixture is on this dark screw, not on one of the traveler screws. Move wire to correct terminal.
- Both switches must be in UP position for light to turn on
- Cause: Travelers are crossed — Switch 1 traveler 1 is connected to Switch 2 traveler 2 Fix: This is functional but non-standard. To correct: swap the two traveler wires at either switch box so both switches use matching traveler assignments.
Frequently asked questions
Why does my 3-way switch light work from one switch but not the other?
One traveler wire is likely not connected or is connected to the wrong terminal. The most common cause is a wire on the common terminal of one switch that should be on a traveler terminal, or a traveler wire that is disconnected. Verify with a multimeter: at switch 1, the common should read line voltage. At switch 2, toggle switch 1 and verify voltage alternates between the two traveler terminals. The common of switch 2 should switch the light.
How do I add a third control location to a 3-way circuit?
Install a 4-way switch between the two 3-way switches. The 4-way switch connects to the existing traveler wires and uses two additional traveler wires to the second 3-way switch. A 4-way switch has four terminals — two inputs and two outputs — and its internal crossbar either passes or crosses the two traveler signals. Multiple 4-way switches can be added in series for corridors with many entry points.
Can I use smart switches for a 3-way circuit?
Yes, but most smart switch systems use a "smart" switch at one location and a "remote" or "accessory" switch at the other — not two identical smart switches. The smart switch contains the electronics and requires LINE, LOAD, NEUTRAL, and TRAVELER connections. The accessory switch connects only to power and traveler. Read the specific brand instructions — Lutron, Leviton, and GE all use different wiring schemes for their smart 3-way systems.
What is the black screw on a 3-way switch for?
The black (dark-colored) screw is the COMMON terminal — the most important terminal on a 3-way switch. Hot power (from panel) connects to the common of the first switch. Switched hot (going to fixture) connects to the common of the second switch. The two brass screws on the same side are traveler terminals — they connect to each other via the traveler wires between the two switch boxes.
How do I test which terminal is COMMON on an unmarked 3-way switch?
Use a multimeter in continuity mode. Test all three terminal combinations: common-to-traveler1 and common-to-traveler2 should each show continuity in one switch position (not both at the same time). The terminal that alternates continuity with each of the other two terminals as you flip the switch is the COMMON. The two terminals that are never connected to each other are the travelers.
Sources and verification
Review status: Not independently reviewed. Automated topology checks confirm stored terminals and routes, not the correctness of manufacturer pin assignments, ratings, regional codes, or installation decisions. Verify those claims against the current primary documentation before use.
- IEC 61082-1:2014 — Rules for electrotechnical documents — International Electrotechnical Commission. Supports: General diagram, drawing, table, and reference-designation presentation conventions. Checked 2026-07-15.
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