Wiring Methods & Materials

Texas Journeyman Electrician Exam — 2026 NEC (NFPA 70)

Learning Objectives

Upon completing this chapter, you will be able to:

6.Identify the scope and hierarchy of NEC Chapter 3 wiring methods, including when a wiring method is permitted, where it is prohibited, and how to select the correct method for a given occupancy or environment.

7.Apply the general installation requirements for conductors, including ampacity correction and adjustment factors, conductor identification, and support requirements.

8.Distinguish between metallic and nonmetallic conduit and tubing systems, their trade sizes, bending radii, and support intervals.

9.Understand the specific rules for cable assemblies (NM, NMC, NMS, AC, MC, SE, USE) and their permitted uses in residential and commercial settings.

10.Navigate the critical tables (310.16, 310.15(B), 352.30, 358.30, etc.) efficiently during the open-book exam.

11.Recognize common field errors and exam traps related to physical protection, securing, and supporting of wiring methods.

1.1 The Scope of Chapter 3: Wiring Methods and Materials

Chapter 3 of the NEC is the backbone of physical installation. While Chapter 2 covers the calculation of electrical loads (how much current), Chapter 3 governs the physical means of delivering that current safely. The 2026 NEC reorganizes some content, but the fundamental principle remains: All conductors must be installed within an approved wiring method unless specifically permitted otherwise.

Key Concept – The "Chain of Articles": You cannot simply choose a wiring method. You must verify three things:

16.Article 300 (General Requirements): Applies to all wiring methods unless modified by the specific article.

17.The Specific Article (e.g., 358 for EMT): Contains the unique rules for that method.

18.Article 110 (Requirements for Installations): Governs the equipment and conductors themselves.

Exam Trap: Many candidates forget that Article 300 applies in addition to the specific article. For example, when installing EMT (Article 358), you must still comply with 300.15 (boxes and conduit bodies) and 300.4(D) (physical protection of conductors).

1.2 General Requirements for Conductors (Article 300)

Before looking at pipes and cables, you must master the rules that apply to all conductors.

300.3 – Conductors of the Same Circuit: All conductors of the same circuit (phase, neutral, and equipment grounding conductor) must be contained within the same raceway, cable, or trench. This prevents inductive heating and ensures the magnetic fields cancel.

Exception: Parallel conductors (per 310.10) may be run in separate raceways, but the raceways must have the same physical characteristics.

300.4 – Protection Against Physical Damage: Conductors must be protected where they pass through studs, joists, or rafters.

Nonmetallic-sheathed cable (NM): If a stud or joist is not notched, the cable must be at least 1¼ inches (32 mm) from the nearest edge. If this cannot be met, you must install a steel plate or bushing at least 1/16 inch (1.6 mm) thick.

Raceways: When installed in exposed areas subject to physical damage, use rigid metal conduit (RMC) or intermediate metal conduit (IMC). PVC is not permitted where physical damage is severe.

300.7 – Raceways Exposed to Different Temperatures: Where a raceway passes from a warm area to a cold area (e.g., a walk-in freezer), you must install a seal to prevent condensation from entering the raceway.

300.11 – Securing and Supporting: Raceways and cables must be securely fastened in place. You cannot use the ceiling support wires (safety cables) of a suspended ceiling to support wiring methods, except for supporting the raceway or cable itself if the wire is a dedicated support wire.

300.15 – Boxes, Conduit Bodies, or Fittings: A box must be installed at every splice point, outlet, switch point, junction point, or pull point. The only exception is when using a wiring method that is listed for continuous unspliced runs (e.g., some manufactured wiring systems).

1.3 Conductor Ampacity and Sizing (Article 310)

This is the most calculation-heavy area of the wiring methods chapter.

310.3 – Conductors: Conductors must be copper, aluminum, or copper-clad aluminum. Solid conductors are limited to size 10 AWG and smaller for general wiring (larger sizes must be stranded for flexibility).

Table 310.16 – Ampacities: This is the primary table. It provides ampacity for conductors rated 0–2000 volts, based on:

Insulation temperature rating: 60°C (TW, UF), 75°C (THHW, THWN, XHHW), 90°C (THHN, XHHW-2, THWN-2).

Terminal temperature rating: This is the critical trap. The ampacity of the conductor is limited by the lowest temperature rating of any connected termination (breaker, lug, etc.). Most standard breakers are rated 60°C or 75°C. Even if you use 90°C wire, you cannot exceed the 75°C column unless the terminals are specifically listed for 90°C.

310.15(B) – Adjustment and Correction Factors:

Ambient Temperature (Correction): Table 310.15(B)(1) requires you to correct the ampacity based on the ambient temperature of the installation location. The NEC standard is 30°C (86°F). If the ambient is higher, you must reduce the ampacity.

More than 3 Current-Carrying Conductors (Adjustment): Table 310.15(B)(3)(a) requires an adjustment factor when you have more than three current-carrying conductors in a raceway or cable. For 4–6 conductors, multiply by 0.80. For 7–9, multiply by 0.70. For 10–20, multiply by 0.50.

Order of Operations: First, correct for ambient temperature. Second, adjust for conductor count. You do not add the two penalties together; you multiply the base ampacity by both factors sequentially.

310.10 – Conductors in Parallel: Conductors sized 1/0 AWG and larger may be paralleled. Each parallel set must have the same length, conductor material, insulation type, and cross-sectional area. You cannot parallel conductors smaller than 1/0 AWG.

Field Point: A journeyman running 4–6 conductors in a single conduit for a 3-phase motor circuit must remember the 80% adjustment. This often forces an upsizing of the conductor from #10 to #8.

1.4 Metallic Conduit and Tubing

1.4.1 Electrical Metallic Tubing (EMT) — Article 358

EMT is the most common thin-wall conduit in commercial work. It is not threaded; it uses set-screw or compression couplings.

Minimum Size: ½ inch (trade size 16).

Bending: You may use factory elbows or field bends. The total bends between pull points must not exceed 360 degrees (four 90-degree bends). If you exceed this, you must install a pull box or conduit body.

Support (358.30): EMT must be secured within 3 feet (900 mm) of each box, cabinet, or fitting. The supports between boxes must be at intervals not exceeding 10 feet (3.0 m).

Corrosion Protection: Galvanized EMT is suitable for most indoor and damp locations. It is not permitted where subject to severe corrosive influences unless protected.

1.4.2 Rigid Metal Conduit (RMC) — Article 344 and Intermediate Metal Conduit (IMC) — Article 342

RMC is thick-wall, threaded conduit. IMC is a lighter-weight version with the same outside diameter as RMC but thinner walls. Both are permitted in all atmospheric conditions and occupancies.

Support: RMC and IMC must be supported within 3 feet of each box. The support interval is 10 feet for horizontal runs and 20 feet for vertical runs (Table 344.30(B) and 342.30(B)).

Threading: Field threads must be made with a die. You must use a standard conduit wrench; you cannot use stillson wrenches that will damage the galvanized coating.

1.4.3 Flexible Metal Conduit (FMC) — Article 348 and Liquidtight Flexible Metal Conduit (LFMC) — Article 350

FMC (Greenfield) is used for the final connection to motors and equipment that require vibration isolation.

Support: FMC must be secured within 12 inches of the box and at intervals not exceeding 4.5 feet (1.4 m).

Length Limitation: FMC is permitted for equipment connections up to 6 feet in length. Longer runs require a different wiring method.

Bonding: FMC is not an effective equipment grounding conductor unless the fittings are listed and the length is 6 feet or less. For longer lengths, you must install an internal bonding jumper.

1.5 Nonmetallic Conduit and Tubing

1.5.1 PVC Conduit (Article 352)

Rigid PVC conduit is the standard for underground installations and corrosive environments.

Expansion: PVC expands significantly with temperature. You must install expansion fittings where the conduit crosses building expansion joints or where the length of run exceeds 25 feet in areas with high temperature differentials.

Support (352.30): PVC must be supported within 3 feet of each box. The horizontal support interval is 3 feet for trade sizes ½ through 1, and 5 feet for trade sizes 1¼ through 2. Vertical runs have different intervals (Table 352.30).

Bending: PVC can be field-bent using a hot box. The minimum bending radius is per Table 2 of Chapter 9.

Physical Damage: PVC is not permitted to be used where subject to physical damage unless it is installed in a location where it is protected (e.g., behind a wall or in a trench).

1.5.2 Electrical Nonmetallic Tubing (ENT) — Article 362

ENT is a corrugated, flexible nonmetallic raceway. It is permitted only in buildings of three stories or less and only for concealed locations (inside walls, floors, or ceilings). It is not permitted in exposed locations or in plenums.

1.6 Cable Assemblies

1.6.1 Nonmetallic-Sheathed Cable (NM, NMC, NMS) — Article 334

This is "Romex." It is the standard for residential wiring.

Permitted Uses: NM is permitted in one- and two-family dwellings, and in multifamily dwellings and commercial structures of Type III, IV, and V construction (combustible framing). It is not permitted in high-rise buildings of Type I or II (noncombustible) construction.

Prohibited Uses: NM cannot be used where exposed to excessive moisture, corrosive conditions, or where subject to physical damage. It cannot be embedded in concrete or masonry.

Support (334.30): NM must be secured within 12 inches of every box, cabinet, or fitting. The supports between boxes must be at intervals not exceeding 4.5 feet (1.4 m).

Bending Radius: The radius of the bend must not be less than 5 times the diameter of the cable for cables rated 2 AWG and smaller.

Protection Through Studs (334.17): As noted in 300.4, you must protect the cable with a steel plate if the hole is less than 1¼ inches from the edge of the framing member.

1.6.2 Armored Cable (AC) — Article 320 and Metal-Clad Cable (MC) — Article 330

AC ("BX") has an internal bonding strip. MC has an internal or external equipment grounding conductor.

AC Cable: Permitted for dry locations only. It is often used in commercial buildings where NM is not allowed.

MC Cable: More versatile. It is permitted in wet locations if the conductors are rated for wet locations (e.g., THWN-2) and the outer jacket is impervious to moisture.

Support: Both AC and MC must be secured within 12 inches of the box and at intervals not exceeding 6 feet (1.8 m).

Cutting: You must use a hacksaw or a specialized cutter. You cannot use a pipe cutter, which will crush the armor and damage the conductors.

1.6.3 Service-Entrance Cable (SE and USE) — Article 338

SE cable is used for service conductors. USE cable is rated for underground installation only.

SE Cable: Can be used for feeders and branch circuits in certain conditions. The uninsulated neutral conductor is permitted for use as the grounded conductor in a 120/240-volt, single-phase, 3-wire service.

USE Cable: Cannot be used for interior wiring. It is for underground service laterals only.

1.7 Boxes and Fittings (Article 314)

Boxes must be installed at every splice and outlet point. The critical calculation is box fill (314.16).

Box Fill Calculation: You must count the number of conductors, devices, and fittings that enter the box.

Each conductor passing through the box counts as one.

Each conductor terminating in the box counts as one.

Each internal cable clamp counts as one (based on the largest conductor).

Each device (switch or receptacle) counts as two (based on the largest conductor connected to the device).

Equipment grounding conductors count as one total, regardless of how many are present.

Table 314.16(A): This table provides the maximum number of conductors allowed in standard metal boxes. For example, a 4-inch square box with a depth of 2⅛ inches has a volume of 30.3 cubic inches and is allowed to hold a specific number of #14 or #12 conductors.

Sizing: If you have a mix of conductor sizes, you must calculate the total volume required using Table 314.16(B) (volume per conductor: #14 = 2.0 in³, #12 = 2.25 in³, #10 = 2.5 in³).

Exam Trap: Do not forget to count the internal clamps and the device yoke. A common error is to count the conductors but forget the two counts for the receptacle.

1.8 Code Navigation: Where to Find It

Concept	NEC Reference
General Requirements for Wiring Methods	Article 300
Conductor Ampacity Table	Table 310.16
Ambient Temperature Correction Factors	Table 310.15(B)(1)
Adjustment Factors for >3 Conductors	Table 310.15(B)(3)(a)
EMT (Electrical Metallic Tubing)	Article 358
EMT Support Intervals	358.30
RMC (Rigid Metal Conduit)	Article 344
IMC (Intermediate Metal Conduit)	Article 342
FMC (Flexible Metal Conduit)	Article 348
PVC (Rigid Nonmetallic Conduit)	Article 352
ENT (Electrical Nonmetallic Tubing)	Article 362
NM Cable (Romex)	Article 334
AC Cable (BX)	Article 320
MC Cable	Article 330
SE / USE Cable	Article 338
Box Fill Calculations	314.16, Tables 314.16(A) & (B)
Bending Radius for Raceways	Chapter 9, Table 2
Maximum Number of Bends (360°)	300.34 / Specific Articles

1.9 Practical Field Points and Common Exam Traps

107.The 12-Inch Rule: NM, AC, and MC cable must be secured within 12 inches of the box. EMT and PVC must be secured within 3 feet of the box. Do not mix these up. The 12-inch rule is for cables; the 3-foot rule is for raceways.

108.The 360-Degree Rule: You cannot have more than 360 degrees of total bend between pull points. This is a physical law of pulling wire, not just a code rule. If you have a run with three 90s and two 45s, you are at 360 degrees and must add a pull box.

109.Terminal Temperature Ratings: Always check the breaker or panelboard terminal rating. If it is 75°C, you can use the 75°C column of Table 310.16. If it is 60°C (common on older equipment), you are limited to the 60°C column, even with 90°C wire.

110.Neutral as a Current-Carrying Conductor: For a 3-phase, 4-wire wye system (208Y/120V or 480Y/277V), the neutral is considered a current-carrying conductor because it carries the unbalanced load. This means you must count it for the adjustment factors in 310.15(B)(3)(a). For a single-phase 120/240V system, the neutral is not counted if it only carries the unbalanced current.

111.Supporting Ceiling Wires: You cannot use the ceiling grid support wires to support conduit or cable. You must install a separate support wire (usually 12 AWG) or use a trapeze.

112.PVC Expansion: In Texas, with high summer temperatures, a long PVC run across a parking lot or rooftop will expand. If you do not install expansion fittings, the conduit will buckle and pull apart at the couplings.

113.BX vs. MC Bonding: AC cable relies on the armor and the internal bonding strip for ground. MC cable has a separate green ground wire. When terminating MC, you must strip the jacket back and use an anti-short bushing (redhead) to protect the conductors from the cut armor.

Summary

Mastering Chapter 3 requires a dual approach: memorizing the specific support intervals and permitted uses for each wiring method, and understanding the general rules of Article 300 and 310 that apply universally. In the open-book exam, your speed will depend on your ability to navigate to the correct table quickly. Use the Code Navigation section above as your quick-reference map. Remember that the physical installation rules are designed to protect the conductor from heat, moisture, and physical damage—when in doubt, ask yourself which hazard the code rule is addressing.

Wiring Methods & Materials