Four-Way Switching: Multi-Location Control with Intermediate Switches

What a Four-Way Switch Adds to a Three-Way System

A four-way switch lets you control the same light from three or more locations by inserting an “intermediate” switching point into an existing two-location (three-way) setup. It does not connect to the load or the line directly; instead, it only switches the two traveler conductors coming from one three-way to the two travelers going to the other three-way.

Think of the four-way as a device that can connect two incoming traveler wires to two outgoing traveler wires in one of two patterns: straight-through or crossed. This is why it has four terminals (plus ground): two terminals are one traveler pair, and two terminals are the other traveler pair.

How Four-Way Switches Route Travelers (Straight-Through vs Crossed)

Inside a four-way switch are two linked changeover contacts. Flipping the toggle changes how the traveler pairs are connected:

• Straight-through: Traveler A-in goes to Traveler A-out, and Traveler B-in goes to Traveler B-out.
• Crossed: Traveler A-in goes to Traveler B-out, and Traveler B-in goes to Traveler A-out.

This is easiest to see with a simple mapping diagram. Label the two travelers coming from the “upstream” side as T1 and T2, and the two travelers leaving toward the “downstream” side as T1' and T2'.

FOUR-WAY INTERNAL ROUTING (conceptual)  Position 1 (straight):   T1  ───────── T1'   T2  ───────── T2'  Position 2 (crossed):    T1  ───────── T2'   T2  ───────── T1'

Because a three-way system already depends on traveler continuity, the four-way simply changes which traveler is “passed through” at that point, altering whether the overall path from common-to-common is complete.

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Where Four-Ways Must Be Placed (Between Two Three-Ways)

A four-way switch must be installed between the two three-way switches, in the traveler run. It cannot replace a three-way at an end location.

• End locations: must be three-way switches (each has a common terminal).
• Middle locations (one or more): four-way switches (no common terminal; only traveler pairs).

When you add more than one four-way, they are simply chained in series in the traveler path:

3-way (end)  ⇄  4-way  ⇄  4-way  ⇄  ...  ⇄  3-way (end)      (travelers only between these devices)

Terminal Group Identification (How to Tell Which Screws Belong Together)

Four-way switches have four traveler terminals arranged as two pairs. Manufacturers often mark them in one of these ways:

• Two screws of one color + two screws of another color (e.g., two dark and two light), indicating two terminal groups.
• “IN” and “OUT” markings (or “LINE” and “LOAD” on some devices, even though it’s still travelers in/out).
• Paired terminals on the same side of the switch body (common on some designs), where each side is one traveler pair.

What matters is not which side is “in” or “out” (a four-way is usually reversible), but that you keep each cable’s traveler pair landed on the same terminal group. If you split a pair across groups, the switch will still “do something,” but troubleshooting becomes much harder and behavior may be inconsistent.

Practical identification steps at the bench (before installation)

• Look for molded labels: IN/OUT, A/B, or arrows.
• If unlabeled, treat each side of the device as a pair (common layout), but confirm with the included diagram sheet.
• Use a continuity tester with the switch removed (not connected to any wiring): identify which two terminals are connected in one toggle position and how they swap in the other. Mark the two “groups” with tape (e.g., Group 1 and Group 2).

Typical Cable Routing in Hallways and Stairwells

In real homes, multi-location control is common in long hallways, stairwells, and large rooms with multiple entrances. The most common physical routing is “daisy-chaining” boxes along the path of travel, which naturally places four-way switches in the middle boxes.

Common layout: hallway with three control points

• Box 1 (hallway entry): three-way
• Box 2 (middle of hallway): four-way
• Box 3 (other end): three-way

The traveler cable typically runs from Box 1 to Box 2, then Box 2 to Box 3. The light’s feed and switch leg may be at either end depending on the house wiring plan, but the four-way remains in the traveler path only.

Stairwell layout: bottom, landing, top

Often the landing box is physically between the top and bottom, making it a natural four-way location. The key practical point is to keep the traveler pairs intact from cable-to-terminal group-to-cable.

Box-Layout Diagrams: Traveler Pairs, Splices, and Consistency

The diagrams below focus on the part that changes when adding a four-way: the traveler routing through the middle box. They assume you already have two travelers between end switches and you are inserting a middle location.

Diagram 1: Single four-way inserted between two three-ways (traveler-only view)

BOX 1 (3-way end)        BOX 2 (4-way)                 BOX 3 (3-way end)  Travelers out ────────┐   Cable in:  T1,T2          ┌──────── Travelers in   T1 ────────────────┼──> Group A: [  ] [  ] ─────┼────────────── T1   T2 ────────────────┘   Cable out: T1',T2'        └────────────── T2                                 Group B: [  ] [  ]  Notes: - Land the two travelers from Box 1 on one terminal group (Group A). - Land the two travelers going to Box 3 on the other terminal group (Group B). - Do not mix one conductor from each cable into the same group.

Diagram 2: Two four-ways in series (four locations total)

3-way ──(T1,T2)── 4-way #1 ──(T1,T2)── 4-way #2 ──(T1,T2)── 3-way  In each 4-way box:  Cable from previous box = one terminal group  Cable to next box       = the other terminal group

Diagram 3: Practical box wiring with splices (keeping traveler pairs consistent)

In many installations, the four-way box may also contain other pass-through cables (feeds continuing to other loads, neutrals passing through, etc.). The four-way portion should remain clean and identifiable.

BOX 2 (4-way) - recommended organization  Incoming cable from Box 1:   - Traveler pair:  T1 (e.g., red), T2 (e.g., white re-marked)   - Ground: bond to box/device  Outgoing cable to Box 3:   - Traveler pair:  T1' (e.g., red), T2' (e.g., white re-marked)   - Ground: bond to box/device  Splices (if neutrals/feeds present in this box):   - Keep neutrals bundled separately with a wirenut   - Keep always-hot feed splices separate   - Do not tie any neutral or hot feed to the four-way terminals  Device terminations:   - Group A terminals: land T1 and T2 from the incoming cable   - Group B terminals: land T1' and T2' from the outgoing cable

Correct Splicing Practices in Four-Way Boxes (What to Do and What to Avoid)

• Keep traveler pairs physically paired: twist/route the two travelers from the same cable together as they approach the device. This reduces mix-ups during installation and later service.
• Re-identify conductors used as travelers: if a white conductor is used as a traveler, mark it (tape/sleeve) so it is not mistaken for neutral during future work.
• Use pigtails only when needed: four-way traveler conductors typically land directly on the device screws/terminals; avoid unnecessary splices that add failure points.
• Separate “systems” in the box: travelers on the device; neutrals bundled; always-hot splices bundled; grounds bonded. This makes diagnosis faster.
• Torque/termination discipline: ensure each conductor is fully seated under the terminal clamp or wrapped correctly under screw terminals, and that insulation is not pinched under the metal.

Traveler consistency rule (prevents 90% of confusion)

Pick a naming convention and stick to it from end to end:

• Traveler 1 = the red in every cable segment
• Traveler 2 = the re-marked white (or other color) in every cable segment

Then, at every four-way, land the two conductors from the same cable onto the same terminal group. Do not “swap colors” mid-run unless you intentionally document it and re-identify conductors.

Step-by-Step: Adding a Four-Way to an Existing Three-Way Run (Traveler-Focused)

This procedure assumes you are inserting a new middle box between the two existing three-way boxes and rerouting the traveler cable accordingly.

1. Choose the insertion point: select a location physically between the two existing three-way switches where you can route a cable from the first three-way to the new box and from the new box to the second three-way.
2. Plan traveler pair continuity: decide which conductor colors will represent T1 and T2 for every segment. Maintain that convention on both new cable runs.
3. Move the traveler run: remove the original traveler cable between the two three-ways (or repurpose it as one segment if the new box is placed along that route). The goal is: 3-way ⇄ 4-way ⇄ 3-way with two travelers on each segment.
4. Terminate the four-way: land the two travelers from the “upstream” three-way on one terminal group; land the two travelers to the “downstream” three-way on the other terminal group.
5. Dress the box: keep traveler conductors together and away from unrelated splices; fold neutrals and always-hot splices to the back; keep grounds properly bonded.
6. Verify end switches remain end switches: confirm that only the three-way switches have the commons connected (line/common at one end, load/common at the other end in the typical arrangement). The four-way should have only travelers.

Test-and-Diagnose Miswired Four-Ways (Symptoms, Isolation, Re-termination)

Common symptoms of a miswired four-way

Isolation steps (systematic, box-by-box)

1. Start at the four-way box: confirm it has exactly four insulated conductors on the device (two from one cable, two from the other), plus ground. If you see a neutral or always-hot feed on the four-way, that is a red flag.
2. Check terminal grouping: verify that the two conductors from the same cable land on the same terminal group. If one conductor from Cable A and one from Cable B are on Group A, re-terminate so each cable occupies its own group.
3. Confirm traveler pair identity: ensure your chosen T1 color is consistent on both sides. If red is T1 on one segment but is used as T2 on the next, you may get confusing behavior. Correct by re-terminating to restore consistent pairing (or re-identify and document).
4. Inspect for opens: gently tug each conductor at the terminal; a loose clamp/screw can create an intermittent traveler open that mimics “bad switch logic.”
5. Reduce the system to a known-good baseline: temporarily bypass the four-way by connecting travelers straight through (T1-to-T1', T2-to-T2') with wirenuts in the four-way box (device removed). If the two end three-ways now behave correctly, the issue is in the four-way device or its terminations.
6. If multiple four-ways exist: bypass them one at a time (starting closest to one end) to locate which box introduces the fault.

Re-termination strategy (clean reset)

1. Label cables, not just wires: mark the cable coming from the “left” three-way as FROM 3W-A and the cable going to the “right” three-way as TO 3W-B.
2. Land by cable-to-group: put both travelers from FROM 3W-A on Group A; put both travelers from TO 3W-B on Group B.
3. Restore traveler color convention: if your convention is red=T1 and re-marked white=T2, ensure that is true on both cables leaving the box. If not, correct at this box (swap terminations) so the convention continues.
4. Re-test switch behavior: after re-termination, verify that every switch changes the light state regardless of the other switches’ positions. If one location still fails, move to the next four-way (or an end three-way) and repeat the same cable-to-group verification.