8.1 Wiring Methods and Raceways

Why Wiring Methods Matter on the TX Journeyman Exam

Wiring methods and materials make up one of the heaviest content areas on the NEC Knowledge portion of the Texas Journeyman exam — roughly 15 to 20 percent of the 59 knowledge questions. Article 300 sets the universal rules for how conductors are installed and protected; Articles 342 through 362 define each raceway type and where it may and may not be used. Expect code-knowledge questions such as "Which raceway is prohibited in a Class I, Division 1 location?" and scenario questions that require you to identify the correct installation method or minimum clearance.

Article 300 — General Requirements for Wiring Methods

NEC Article 300 applies to all wiring installations unless a specific article modifies it. The most-tested subsections on the Journeyman exam are below.

300.3(A) — All Conductors of the Same Circuit in the Same Raceway

All conductors of the same circuit — including the grounded (neutral) conductor and the equipment grounding conductor (EGC) — must be run in the same raceway, trench, cable, or cord. Running the hot and neutral in separate conduits creates magnetic imbalance, inductive heating, and elevated conductor temperature. This is one of the most frequently tested rules.

Exception: Conductors for spark igniters, certain remote-control and signaling conductors under 50 V, and specific parallel conductor installations per 310.10(G) have defined allowances.

300.4 — Protection Against Physical Damage

When raceways or cables pass through structural members, the NEC requires minimum edge clearances or steel plate protection:

The 1-1/4 in. rule is one of the most frequently tested single numbers on the exam — memorize it.

300.17 — Conductors of Different Insulation Ratings

When conductors with different temperature ratings are installed in the same raceway or cable, the lowest temperature rating governs the allowable ampacity of every conductor in the group. If THHN (90 °C) and THW (75 °C) are pulled together, both are limited to the 75 °C column ampacity — even the THHN.

300.22 — Wiring in Ducts, Plenums, and Other Air-Handling Spaces

Article 300.22 restricts what may be installed in spaces that carry environmental air:

• 300.22(B) — Plenums and ducts specifically fabricated for environmental air: Only listed plenum-rated cable (CMP, CL2P, and similar) or metal raceways (RMC, IMC, EMT, FMC up to 4 ft) and mineral-insulated cable are permitted. Nonmetallic conduit is not allowed.
• 300.22(C) — Other spaces used for environmental air (for example, the area above a suspended ceiling used as a return-air plenum): Wider allowances — MC cable, AC cable, NM cable, and most raceways are permitted when installed per their respective articles.

Exam tip: plenums under 300.22(B) are far more restrictive than other spaces used for environmental air under 300.22(C). Know the difference.

Raceway Types — Comparison

The NEC organizes each raceway in its own article (342 through 362). Every article has a "Uses Permitted" and a "Uses Not Permitted" section — these are the exact subsections the exam references.

Trade Size vs. Metric Designator

The NEC uses trade sizes (inches) alongside metric designators. You will see both on the exam. Memorize the common pairings:

The metric number is the nominal outside diameter in millimeters, rounded. Trade sizes smaller than 1/2 in. (metric 16) are not permitted for most raceway wiring methods — each raceway article sets a minimum trade size of 1/2 in.

Where Each Raceway Is Prohibited — Exam Favorites

• PVC (Article 352): Not permitted in hazardous (classified) locations (352.12) except as Chapter 5 allows. Not used to support luminaires. Schedule 80 may be used where subject to physical damage; Schedule 40 may not.
• EMT (Article 358): Not permitted where subject to severe physical damage (358.12(B)). Minimum trade size is 1/2 in.
• FMC (Article 350): Not permitted as the sole equipment grounding conductor for runs exceeding 6 ft (350.60). Not in hoistways or where subject to physical damage.
• ENT (Article 362): Not permitted in plenums (300.22(B)), not in hazardous locations, not where subject to physical damage, and not in ambient temperatures above 50 °C.
• LFNC (Article 356): Total length must not exceed 6 ft in a single run unless specifically permitted; not in hazardous locations unless Chapter 5 allows.