Wire a single pole, a three way, a four way and a run with power at the light on a drawn bench, flip the switches, and watch the light answer the circuit you actually built.
Every level runs nonmetallic sheathed cable into nonmetallic boxes, on a 20 ampere general purpose branch circuit in a habitable room. Cable grounding conductors are landed for you at each box. The rest is yours.
That box is the allowance inside 406.30(C). Leave it clear and the check asks for a grounded conductor at every switch box. Tick it and one box is enough.
Each conductor end has a select. It does what the drag does, and the drawing follows.
A three way wired backwards still lights, which makes it a good exam question and a bad thing to learn on the job, because the circuit answers one switch and quietly ignores the other. So the bench does not ask whether the light is on. It runs every switch position, asks whether flipping any one switch changes the light no matter where the others sit, then reads your wiring against the sections that govern it.
If you learned the switch wiring rules as 404.2 and 404.9, the 2026 edition moved them. Article 404 still covers switches as equipment, but the wiring rules for general use snap switches, dimmers and control switches now sit in Article 406 Part III, with the book's moved marker beside them.
The three way and four way rule quoted as 404.2(A) is 406.30(A). The grounded conductor at the switch box, quoted for a decade as 404.2(C), is 406.30(C). Grounding the switch itself, quoted as 404.9(B), is 406.40(B), and the enclosure side is 406.44. What people cite as 200.7(C) is 200.8(C) here, because 200.7 is now the section on identifying grounded conductors.
The requirements read the way they did. The numbers changed, and on an exam written to the 2026 edition the number is what you have to find, so every fault this lab reports carries the section as the 2026 book prints it.
406.30(A) says three way and four way switches are wired so all of the switching happens in the ungrounded conductors, and that in metal raceway or metal armored cable the wiring between switches and outlets follows 300.22(A), the rule on grouping conductors so they do not heat the ferrous metal around them. It carries a short exception: a switch loop is not required to have a grounded conductor.
As a wiring instruction: a three way has three screws. Two are a matched pair and take the travelers running to the other switch. The third is the common, set apart by the maker, and it takes the odd conductor, either the ungrounded supply or the switched leg on to the light. Put the supply on a traveler screw and the light still works from one switch in some positions of the other, which is why the bench runs the whole table.
A four way has two pairs. One takes both travelers from the first three way, the other sends both on to the second, and flipping it swaps which traveler feeds which, reversing the pair without ever becoming the source or the load. Wire it across the wrong pairs and it does nothing, or it stops the run.
406.30(C) asks for the grounded circuit conductor of the controlled lighting circuit at the location where switches control lighting loads, when the load is 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: it leaves a circuit path for an electronic lighting control device.
An allowance is built in. Where several switch locations control the same lighting load and the whole floor area of the room is visible from those locations taken together, the grounded conductor is only required at one of them. That is the checkbox on the bench, and it is what makes the run with power at the light workable with three conductor cable.
Four conditions take the requirement away entirely: a raceway into the box large enough to carry a grounded conductor along with everything else, a snap switch with the kind of integral enclosure 300.17(E) covers, lighting controlled from a remote location, and a switch that controls a receptacle load. Here the method is cable rather than raceway, so the first is closed to you. A further exception covers a replacement switch in a location wired before the section was adopted locally, where the grounded conductor cannot be brought in without taking out finish material.
200.8(A) reserves the continuous white finish, the gray finish and the three stripe finish for the grounded conductor. 200.8(C) is the way out for circuits of 50 volts or more, and it is narrow: 200.8(C)(1)(a) lets a conductor with that finish in a cable assembly serve as an ungrounded conductor where it is re-identified, and that subdivision is where the marking rule sits, not 310.6(A)(3).
The marking goes on at the termination and everywhere else along the run where the conductor is visible and accessible, it encircles the insulation, and the color is anything other than white, gray or green. Tape and paint both do the job. One wrap on one end in the switch box is not what the section describes.
Then the part people miss. 200.8(C)(1)(b) says that in a single pole, three way or four way switch loop the re-identified conductor may be used only for the supply to the switch, not as the return conductor from the switch back to the outlet. So the marked white feeds a switch, and the switched leg comes back to the light on a colored one.
406.40(B) requires snap switches, dimmers and control switches to be connected to an equipment grounding conductor, and to give a metal faceplate a way to reach it whether or not a metal plate is ever installed. It names metal screws into a metal box or cover already on the 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: a replacement where the enclosure has no bonding means and the wiring method carries no grounding conductor, which brings conditions of its own about a nonconducting plate or ground fault protection; certain listed assemblies with a nonmetallic plate, a nonmetallic yoke and no accessible metal parts; and a snap switch with an integral nonmetallic enclosure complying with 300.17(E).
406.44 covers the box: metal enclosures go on equipment grounding conductors under Article 250 Part IV, and a nonmetallic box for a switch gets a wiring method that includes one. The boxes here are nonmetallic, so the pigtail from the splice to the green screw is the connection being asked for. 250.148(A) is why the grounding conductors in a box are joined, and 250.148(B) why pulling the switch out does not break the path onward.
On level four the feed lands in the light box and both three ways sit past it. Between the light box and the first switch you need the supply going out, the switched leg coming back, and the grounded conductor 406.30(C) asks for. A three conductor cable with ground covers it: black out to the common, red back to the lamp, white staying a neutral.
Between the two switches you need two travelers and the switched leg on its way back from the far common. That is three ungrounded conductors in a cable that holds three insulated ones, so the white is one of them and has to be re-identified under 200.8(C). Put it on a traveler, keep the return on the red, and 200.8(C)(1)(b) is satisfied, because a traveler supplies the switch beyond it rather than returning from a switch to the outlet.
That leaves no grounded conductor at the second switch box, which is when the allowance in 406.30(C) matters. Two locations on one load, the whole floor area visible from them together, and the grounded conductor at the first box serves. Untick the box and the check names the section, because without the allowance the run needs a four conductor cable or a second one to the far switch.
Press Show a working set on the three way, then move the conductor on the common at switch box 2 to a traveler screw and the traveler that was there onto the common.
What happens: the light still comes on in two of the four positions, so a quick tap looks fine. The toggle table shows the failure and the checker names 406.30(A).
On the solved three way, set the white of the three wire run at switch box 2 to Not landed.
What happens: two faults. 406.30(C) for the grounded conductor missing at the switch location, with the four conditions and the retrofit exception written out. Then 200.5, because that same white is the neutral on its way to the lamp. With power at the switch, the grounded conductor already passes through every box.
On level four, press Show a working set, then untick the re-identification for the white of the run between the switches. Put it back, then move that white onto the common at switch box 2 and onto the hot splice at switch box 1, with the red on the traveler screws instead.
What happens: both times the light still works from both switches, because tape does not carry current and the circuit does not care which conductor is which color. The first raises 200.8(C)(1)(a), which is where the marking rule sits. The second raises 200.8(C)(1)(b), which allows a re-identified conductor as the supply to the switch and not as the return to the outlet.
The one the maker sets apart, usually darker where the other two are brass and marked common on the strap. It takes the odd conductor, the ungrounded supply at one switch and the switched leg at the other, while the matching screws take the travelers. 406.30(A) puts all of that switching in the ungrounded conductors.
Yes, and the rule is 406.30(C) rather than 404.2(C), because Article 406 Part III now carries the switch connection rules. It applies where switches control lighting on a grounded general purpose branch circuit serving bathrooms, hallways, stairways, and habitable rooms or occupiable spaces. Where several locations control one load and the whole floor area is visible from them together, one carries it.
406.30(C) lists four: a raceway into the box large enough to hold a grounded conductor as well, a snap switch with an integral enclosure of the kind 300.17(E) covers, lighting run from a remote location, and a switch that controls a receptacle load. A separate exception covers a replacement in a location wired before the section was adopted locally, where the grounded conductor cannot be brought in without removing finish material.
Only where it is re-identified. 200.8(C)(1)(a) lets a white in a cable assembly serve as an ungrounded conductor, and it sets the marking: it has to encircle the insulation and be a color other than white, gray or green. 200.8(C)(1)(b) then limits it: in a switch loop the marked conductor is the supply to the switch and never the return to the outlet.
406.40(B) connects snap switches, dimmers and control switches to an equipment grounding conductor and gives a metal faceplate a way to reach it, whether or not a metal plate is installed. That happens through metal screws into a metal box or cover already on the grounding conductor, into a nonmetallic box with an integral means for it, or through a bonding jumper landed on the switch. The exceptions cover certain replacements, certain listed nonmetallic assemblies, and integral nonmetallic enclosures.
Because a three way pair has four positions and a wrong connection usually kills two of them rather than all four. Put the supply on a traveler screw and the light answers one switch in some positions of the other, which reads as working if you only flip one. The test is whether any single switch changes the light from every position of the rest.
Read in the 2026 edition and named by the lab: 406.30(A), 406.30(B) and 406.30(C) for switch connections, 406.40(B) and 406.44 for grounding the switch and its box, 200.4(B), 200.5, 200.8(A) and 200.8(C) for the grounded conductor and the white used as a hot, 200.8(C)(1)(a) for the marking with 310.6(A)(3) behind it for the finish, 250.148 for grounding conductors in a box, 410.51 and 410.90 for the screw shell, 110.7 for an installation free of short circuits, and 300.17(E) and 300.22(A) where Article 406 Part III points at them.
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