10.2 Switches and Device Wiring (NEC Articles 404 & 400)

Why This Matters for the TX Journeyman Exam

Article 404 (Switches) and Article 400 (Flexible Cords and Cables) appear in content outline area 6. Most exam items target NEC Knowledge — switch ratings, the multiway neutral rule, and the cord-substitution prohibitions. These are high-frequency memorization items: a candidate who knows 404.2(A), 404.2(C)(2), and 400.8 will pick up easy points.

Grounded Conductor at Switch Locations (NEC 404.2)

NEC 404.2(A) requires switches to be connected so they interrupt only the ungrounded conductors of a circuit. A switch must never interrupt the grounded (neutral) conductor alone — that would leave energized conductors at the load when the switch is off.

NEC 404.2(C)(2) — the "multiway neutral" rule — requires that in new construction, a grounded (neutral) conductor be present at every switch box controlling lighting loads, including 3-way and 4-way installations, even if that conductor is not used by the current wiring scheme.

Why: smart switches, occupancy sensors, and future devices need a neutral. Run a 3-wire cable (or 4-wire for a 3-way) to every switch box. The neutral must be spliced through the box so it is available; pigtails are required if a device terminates on it. The exception covers switch boxes controlling non-lighting loads (e.g., a receptacle switched at one location only) where a neutral is not required by the load.

Switch Ratings (NEC 404.3, 404.4, 404.14)

NEC 404.3 requires a switch to be rated for the current, voltage, and load type it controls. NEC 404.4 lists voltage ratings:

A T-rated switch is marked "T" and rated for tungsten-filament lamp loads, which have a high inrush current. A 15 A general-use AC snap switch may control a resistive load up to 15 A but only a 2 A tungsten load unless it is T-rated.

NEC 404.14(E): dimmer switches must be rated for the controlled load. A standard incandescent dimmer is typically rated 600 VA maximum; loads above 600 VA require a higher-rated dimmer or multiple dimmers. A dimmer may not control a load exceeding its listed rating. Common dimmer ratings encountered on the exam:

Dimmers must not control loads they are not listed for — a standard incandescent dimmer may not control a fan motor or a low-voltage lighting transformer without an appropriate rating.

Grounding Snap Switches (NEC 404.9(B))

NEC 404.9(B) requires snap switches (including dimmers and metal faceplates) to be connected to an equipment grounding conductor — either through metal mounting screws to a grounded metal box, or directly to the circuit equipment grounding conductor at the switch yoke. Three exceptions survive in the 2023 NEC:

• Exception No. 1: a replacement snap switch may be installed without an equipment grounding conductor connection where no equipment grounding conductor exists in the box, provided the switch is provided with a nonmetallic faceplate with nonmetallic mounting screws OR the circuit is GFCI-protected.
• Exception No. 2: listed nonmetallic-yoke assemblies with integral grounding means are permitted.
• Exception No. 3: snap switches with integral nonconductive enclosures are permitted where listed.

The 2023 NEC additionally expanded NEC 250.130(C) to give six options for routing an equipment grounding conductor back to a replacement snap switch where one is added — these options include connecting to any grounding electrode, the grounded conductor at the service, or a grounding-type receptacle on the same branch circuit.

Flexible Cords and Cables (Article 400)

NEC 400.7 lists permitted uses of flexible cords:

• Pendants for luminaires or fixtures
• Wiring of luminaires
• Connection of portable luminaires, portable and mobile signs, and appliances
• Elevator cables
• Connection of stationary equipment to facilitate frequent interchange (e.g., a dishwasher, a water heater with a cord)
• Prevention of transmission of noise or vibration
• Listed data processing cables

NEC 400.8 lists uses NOT permitted — high-frequency exam items:

• As a substitute for the fixed wiring of the structure
• Where run through holes in walls, ceilings, or floors
• Where run through doorways, windows, or similar openings
• Where attached to building surfaces
• Where concealed behind walls, ceilings, or floors
• Where installed in raceways (except short lengths for fixture whips per 410.117(C))

Cord Types (NEC 400.13)

Letter suffixes: O = oil-resistant jacket, W = weather/water resistant, T = thermoplastic, J = junior service (smaller than the same letter without J).