Four question shapes come out of a three-way, and each one turns on a different section

What the exam asks about a three-way

Four shapes come up again and again. Which screw is the common and what lands on it. Whether the white in a given cable is a neutral or a re-identified ungrounded conductor, and what marking makes that legal. Whether the grounded conductor has to be present at that switch location, and which allowance or condition releases it. And whether the switch and its box are grounded the way the code describes.

Be honest about the shape of the bank here. Across our 500 questions only one stem puts a multi-location switching scenario in front of you, and it asks which switching a stairway needs: a dwelling with an interior stairway of eight risers between two floor levels, where the answer is a wall switch at each of the two floor levels. Section 210.70 asks for that wherever the stairway between floor levels holds six or more risers, and the distractors are a single switch at the top, a single switch at whichever level is used more, and a sensor standing in for the switching. Automatic control is permitted on top of the required switching, and it never stands in for it.

That matters for how you study. The connection questions are drawn from the sections below and they reward reading four lines in the book. The switching questions are drawn from 210.70 and they reward knowing which rooms and which stairways the section names, which sits alongside the lighting outlet material on receptacle spacing.

What a three-way actually does

Two switches, one light, and either switch changes it. That's a different circuit shape from a single pole with an extra screw. Each three-way is a single pole double throw device, so one conductor comes in and gets sent to one of two places.

A three-way has three screws. Two are a matched pair and take the travelers, the two conductors running between the two switches. The third is the common, set apart by the maker, usually a darker screw and often marked on the strap.

The common takes the odd conductor. At the switch nearest the supply that's the ungrounded feed. At the switch nearest the light it is the switched leg going on to the lamp. Between them, the travelers carry whichever one of the pair is live at that moment. Flip either switch and you change which traveler is energized at one end while the other end is still looking at a fixed one.

Section 406.30(A) is the rule underneath all of that: three-way and four-way switches are wired so that all switching happens only in the ungrounded circuit conductors. Its companion, 406.30(B), says switches leave the grounded conductors of circuits connected, with an exception where every circuit conductor opens at the same time. A three-way satisfies that easily, which is why it's easy to test you on.

Power at the switch or the light

There are two ways the cable can land, and the exam asks about both because the conductor count differs.

Power at the switch is the friendly one. The feed arrives at the first switch box, so the ungrounded conductor lands on that common and the grounded conductor passes straight through the box on its way to the lamp. A three conductor cable then runs between the two switches carrying two travelers, and a two conductor cable goes from the second switch to the light with the switched leg off that common.

Power at the light is where the counting gets tight. The feed lands in the light box and both switches sit past it. Between the light box and the first switch you need three things: the supply going out, the switched leg coming back, and a grounded conductor for the switch location. A three conductor cable covers that, with the white staying a neutral. Between the two switches, though, you need two travelers plus the return on its way back from the far common. That's three ungrounded conductors inside a cable holding three insulated ones, so one of them is the white, and it has to be re-identified before it can do that job.

The white that becomes an ungrounded conductor

Section 200.8(A) reserves the white finish, the gray finish and the three stripe finish for the grounded conductor. That's the default, and the way out of it is narrow.

Section 200.8(C) covers circuits of 50 volts or more. A conductor with that finish inside a cable assembly may serve as an ungrounded conductor where it is permanently re-identified, and 200.8(C)(1)(a) is where the marking itself sits. It points at 310.6(A)(3) only for the finish that keeps an ungrounded conductor distinguishable from a grounded or a grounding one.

What the marking has to be is specific. It goes on at the termination and at every other place along the run where the conductor is visible and accessible, it encircles the insulation, and it is any color other than white, gray or green. Tape does it and paint does it. One wrap on one end in the switch box falls short.

Whether that switch box owes a neutral

Section 406.30(C) asks for the grounded circuit conductor of the controlled lighting circuit at the location where switches control lighting loads, where that load sits on a grounded general-purpose branch circuit serving a bathroom, a hallway, a stairway, or a habitable room or occupiable space as the building code defines it. The informational note gives the reason plainly: it leaves a circuit path for an electronic lighting control device.

An allowance is built in and it matters on a three-way. Where several switch locations control the same lighting load, and the entire floor area of the room is visible from those locations taken together, the grounded conductor is required at one of them only. That allowance is what makes a run with power at the light workable on three conductor cable.

Four conditions take the requirement away outright: conductors entering the switch box through a raceway large enough for all the conductors including a grounded one, a snap switch with the kind of integral enclosure 300.17(E) covers, lighting in the area controlled from a remote location, and a switch controlling a receptacle load. On a cable job the first of those is closed to you.

There's also an exception for a replacement or retrofit switch in a location wired before the section was locally adopted, where the grounded conductor cannot be brought in without removing finish material. And the section is explicit the other way too: where a grounded conductor is extended to a switch location, it connects to switching devices needing line to neutral voltage to run their electronics in standby.

Grounding the switch and its box

This is a separate rule from everything above and it lives in a different section. Section 406.40(B) requires snap switches, dimmers and control switches to be connected to an equipment grounding conductor, and to provide a means for a metal faceplate to reach that conductor whether or not a metal plate is ever fitted.

It names the ways: metal screws into a metal box or cover already on the equipment grounding conductor, screws into a nonmetallic box with an integral means for it, or a bonding jumper run to the grounding termination on the switch. Three exceptions follow, covering certain replacements where the enclosure has no bonding means, certain listed assemblies with a nonmetallic plate and yoke and no exposed metal, and a snap switch with an integral nonmetallic enclosure.

Section 406.44 leaves the device alone and covers the box. Metal enclosures for switches go on equipment grounding conductors under Article 250 Part IV, and a nonmetallic box for a switch is installed with a wiring method that provides or includes an equipment grounding conductor. In a plastic box that means the pigtail from the splice to the green screw is the connection being asked for, which is the same reasoning worked through on grounding and bonding.

Where these rules live in the 2026 book

If you learned these as 404.2 and 404.9, the numbers moved. Article 404 still covers switches as equipment, and the wiring rules for general use snap switches, dimmers and control switches now sit in Article 406 Part III, with 406.30 carrying the moved marker in the margin. The map is short enough to hold.

The requirements read the way they always did. Only the numbers changed, and on a paper written to the 2026 edition the number is the thing you have to find. The wider move is covered on switches, and the same 2026 renumbering pattern reaches Article 300 and Article 312, which is set out on wiring methods.

What a miswire costs, and what to do

The reason these items are written the way they are is that a miswired three-way still turns the light on. A three-way pair has four switch positions, and a wrong connection usually kills two of them while leaving two working, so flipping one switch appears to prove the job. The only check that finds it is walking every combination and confirming that each switch changes the light from every position of the other. That's also why a choice putting the supply on a traveler screw reads as plausible in an exam option, since the circuit responds to what connects to what and ignores conductor colors and screw names.

Before test day, do four things. Read 406.30(A), (B) and (C) end to end once, including the conditions and the exception under (C). Read 200.8(C)(1)(a) and 200.8(C)(1)(b) back to back, because the second one is the half that decides items. Read 406.40(B) and 406.44 together so the device rule and the enclosure rule stay separate. Then put publisher-supplied tabs on 406.30 and on 200.8, since homemade flags are refused at the door and marking the book during the session is refused as well.

Where you want the connections drawn and the conductor count worked through case by case, the three way switch wiring question set carries that version. The four-way case builds straight on top of it and is covered on four-way switch wiring.

Questions people ask

Which wire goes on the common of a 3-way switch?

The odd conductor. At the switch nearest the feed the common takes the ungrounded supply, and at the switch nearest the light it takes the switched leg going on to the lamp. The common is the screw the maker sets apart, usually darker than the other two and often marked on the strap. The matching pair of screws take the travelers, which run between the two switches and carry whichever of the pair is live at that moment. Section 406.30(A) requires that all of that switching happen only in ungrounded conductors.

Can a white conductor be used as a traveler?

Only where it is permanently re-identified. Section 200.8(C)(1)(a) allows a conductor with a white, gray or three stripe finish inside a cable assembly to serve as an ungrounded conductor, and it carries the marking requirement: the marking encircles the insulation, is any color other than white, gray or green, and goes on at the termination and at every other place along the run where the conductor is visible and accessible. As a traveler it supplies the switch beyond it, which satisfies 200.8(C)(1)(b).

Does a 3-way switch location need a neutral?

The switch does not, and the location often does. Section 406.30(C) asks for the grounded conductor of the controlled lighting circuit at switch locations on a grounded general-purpose branch circuit serving bathrooms, hallways, stairways, and habitable rooms or occupiable spaces. An allowance matters here: where several switch locations control one load and the entire floor area of the room is visible from them taken together, one location carries it. Four conditions remove the requirement outright, and an exception covers replacement switches where finish material would have to come out.

Where did 404.2 and 404.9 go in the 2026 edition?

Into Article 406 Part III. The three-way and four-way rule quoted for years as 404.2(A) is 406.30(A). The grounded conductor at the switch box, quoted as 404.2(C), is 406.30(C). Grounding the switch, quoted as 404.9(B), is 406.40(B), and the enclosure side of it is 406.44. What people cite as 200.7(C) is 200.8(C) here, because 200.7 is now the section identifying grounded conductors. The requirements read as they always did, and on a paper written to the 2026 edition the number is what you have to find.

What switching does a stairway need?

Section 210.70 asks for a wall switch at each floor level and at each landing level that includes an entryway, where the stairway between them holds six or more risers. Our question bank puts an eight riser stairway between two floor levels in front of you and offers a single switch at the top, a single switch at whichever level is used more, and a sensor in place of switching. Walking down a dark stair to reach the only switch is the hazard, and automatic control is permitted on top of the required switching.

Why does a miswired 3-way still turn the light on?

Because the circuit responds to what is connected to what, with no regard for conductor color or screw names. A three-way pair has four switch positions, and most wrong connections leave a working path in some combination of the two, so flipping one switch looks like proof that the job is right. Walking all four positions is the only check that finds it. That's also why an exam option putting the supply on a traveler screw reads as plausible, and why the item exists at all.