Chapter 4: Conductors, Cables, Raceways, and Enclosures
Theory tells you how much current a load wants. This chapter is about choosing wire and raceway that can carry that current safely — and looking up the NEC rules Utah's exam expects you to navigate.
On the Journeyman written exam, Conductors & Cables and Raceways & Enclosures are each significant question blocks. Treat this chapter as a field guide to Articles 300, 310, 312, 314 (preview), and the raceway articles in Chapter 3.
4.1 Conductor Materials and Stranding
Copper is the default for most branch-circuit work: lower resistance, smaller size for a given ampacity, reliable terminations.
Aluminum and copper-clad aluminum appear on feeders and services. Aluminum needs:
- Correct connector listing (Cu/Al)
- Proper oxide treatment / inhibitor where required by instructions
- Correct torque
- Awareness that aluminum needs larger size than copper for similar ampacity
Solid vs stranded: Solid is common in smaller branch-circuit sizes; stranded is more flexible and required/preferred as sizes grow. Flexible cords use fine stranding — and cords are not a substitute for permanent building wire.
4.2 Insulation Types You Must Recognize
Insulation type letters encode temperature rating and environment. Examples (verify exact listings in NEC Table 310.4(A) / your edition's insulation table):
| Type (examples) | Typical idea |
|---|---|
| TW | 60°C, wet or dry (limited modern use) |
| THW / THWN | Often 75°C wet ratings depending on type |
| THHN / THWN-2 | Common building wire; THHN dry 90°C, dual-rated wet when marked THWN-2 |
| XHHW / XHHW-2 | Cross-linked, common on feeders |
| USE / RHW | Underground / wet location styles |
Critical exam habit: Termination temperature, not the 90°C column alone, often limits ampacity. Many breakers and lugs are rated 60°C or 75°C. You may install 90°C-insulated wire (THHN) but still select ampacity from the 75°C column when terminations require it (with the usual Code conditions).
4.3 AWG and kcmil
American Wire Gauge: larger AWG number = smaller wire. 14 AWG is smaller than 10 AWG. After 4/0 AWG, sizes are in kcmil (thousands of circular mils): 250, 350, 500, etc.
Memorize approximate copper ampacities only as a sanity check — always confirm with Table 310.16 (or the numbering in your 2023 NEC) under the correct temperature column and conditions of use.
Common copper branch-circuit starting points many electricians know (75°C column, before adjustments — verify in the Code book):
- 14 AWG → 15 A overcurrent typical maximum for most general circuits
- 12 AWG → 20 A
- 10 AWG → 30 A
Small conductors have special rules: 14, 12, and 10 AWG copper are limited in overcurrent protection for general use even when ampacity tables show more under some conditions.
4.4 Ampacity Selection Process
A reliable exam sequence:
- Determine load current (continuous → 125%, noncontinuous as calculated, apply Article 220 demand where required).
- Choose conductor material and insulation.
- Find base ampacity in the ampacity table for the temperature rating allowed by terminations and equipment.
- Apply adjustment factors for more than three current-carrying conductors in a raceway/cable.
- Apply correction factors for ambient temperature other than the table basis (usually 30°C).
- Ensure the resulting ampacity ≥ required load current.
- Size overcurrent protection per Article 240 (next chapter), including round-up rules and continuous-load rules.
- Check voltage drop (Chapter 3) — may force a larger size even when ampacity was fine.
4.4.1 Current-carrying count reminders
Typically counted as current-carrying:
- Ungrounded conductors
- Neutral that carries only unbalanced current in a balanced multiwire circuit may have exceptions — read 310 carefully for when neutrals count
- EGC generally does not count as current-carrying for adjustment
When adjustment applies, ampacity is reduced — sometimes requiring upsizing.
4.5 Cable Types
NM (nonmetallic-sheathed cable) — common in dwelling wood-frame work where permitted. Dry locations, follow support and protection rules, not for embedding in concrete in the general case.
UF — underground feeder cable, wet location / direct burial where permitted.
AC / MC — armored / metal-clad cables. Watch bonding strip requirements and connector types. MC is widely used in commercial work.
SE / SER / USE — service-entrance style cables; know where each is permitted (USE generally not as interior branch-circuit substitute without following specific rules).
Flexible cord (SO, SJO, etc.) — appliances, pendants, temporary — not permanent substitute for Chapter 3 wiring methods.
Exam questions often ask: Is this wiring method permitted in this location? Read the article's "uses permitted / not permitted" lists.
4.6 Raceways: Purpose and Trade-Offs
A raceway encloses and protects conductors, provides a path for pulls, and in metallic forms can serve as an equipment grounding path when installed as a complete Code-compliant system.
| Raceway | Notes |
|---|---|
| EMT | Thin-wall steel, common commercial, threadless fittings |
| RMC / IMC | Heavy / intermediate metal conduit, physical protection |
| PVC (Schedule 40/80) | Corrosion, corrosion resistance; expansion fittings; not a grounding means alone |
| FMC / LFMC | Flexible metal / liquidtight flexible metal |
| ENT | Electrical nonmetallic tubing ("smurf tube") where permitted |
| Wireways / auxiliary gutters | Wire management, fill rules differ |
4.6.1 Conduit fill
You may not stuff unlimited wires into a raceway. NEC Chapter 9 Tables 1, 4, and 5 (and Informative Annex C for common conductor combinations) control fill.
Typical Table 1 limits:
- 1 conductor: up to 53%
- 2 conductors: up to 31%
- Over 2 conductors: up to 40%
Example process: Find conductor cross-sectional area (Table 5), multiply by count, compare to 40% of raceway internal area (Table 4). Or use Annex C when conductors are all the same size/type.
Nipples (≤ 24 inches between boxes) have different fill allowances — a favorite exam detail.
4.7 Bends, Support, and Securing
Each raceway article specifies:
- Maximum degrees of bend between pull points (often 360° total)
- Support intervals
- Securing near boxes/terminations
- Bushings / fittings for protection of conductor insulation
Utah's practical exam includes conduit bending (3-point and 4-point bends, box offsets, fitting between boxes). Written questions may ask theoretical limits; the practical tests craftsmanship — straight, plumb, level, and clearance over obstacles.
4.8 Enclosures and Cabinets
Cabinets, cutout boxes, and meter sockets (Article 312) protect devices and terminations. Watch:
- Working clearance in front (Article 110)
- Cabinets rated for the environment (indoor/outdoor, NEMA type)
- Wire-bending space at terminals for larger conductors
- Unused openings closed
Boxes (Article 314) get deeper treatment in Chapter 7 for box fill, but remember: every splice and device needs an accessible box (with listed exceptions).
4.9 Environmental and Installation Conditions
Article 300 themes:
- Protect conductors from physical damage
- Seal raceways where needed against moisture/gas migration
- Maintain free air / burial depths for underground installations (Tables for cover)
- Keep conductors of different systems separated where required
- Identify high-leg, neutrals, IG conductors, etc., with correct colors/markings
4.9.1 Color identification (typical U.S. practice — confirm Code/local rules)
- Grounded conductor (neutral): white or gray
- Equipment grounding: green, green with yellow stripe, or bare
- Ungrounded: any other colors (commonly black, red, blue for 120/208; brown, orange, yellow for 277/480 — shop standards vary)
- High-leg (delta): orange identification where required
4.10 Direct Burial and Underground
Know that minimum cover depths depend on wiring method and whether GFCI / residential branch circuits allow reduced cover in some rows of the burial table. PVC vs RMC vs cable change the number. When a question gives a location (parking lot, under dwelling, under driveway), go to the underground cover table — do not guess.
4.11 Parallel Conductors
Large ampacities sometimes use conductors in parallel. Rules include:
- Same length, material, size, insulation
- Same termination method
- Proper raceway arrangement
- Minimum size thresholds in the Code
4.12 Practice Problems
- Why might you use the 75°C ampacity column for THHN copper even though THHN is rated 90°C dry?
- You have four current-carrying 12 AWG copper THHN conductors in one EMT. What extra step does ampacity require beyond Table 310.16?
- Does an equipment grounding conductor normally count in the "more than three current-carrying conductors" adjustment?
- What Chapter 9 fill percentage generally applies when there are more than two conductors in a raceway?
- NM cable is proposed for a wet location outdoor feeder. What is the likely Code problem?
- A nipple under 24 inches long is filled with many conductors. Why might that still be acceptable when the same fill in a long conduit run would not?
4.12.1 Answers
- Terminations on breakers/equipment are often limited to 75°C (or 60°C); conductor ampacity is limited by the lowest applicable rating in the system.
- Apply ampacity adjustment factors for more than three current-carrying conductors.
- No — EGCs are generally not counted as current-carrying for that adjustment.
- 40% (Table 1).
- Standard NM is for dry locations; wet location needs a wet-rated method (UF, conduit with wet-rated conductors, etc.).
- Short nipples have higher allowable fill (different rule than standard 40% raceway fill).
4.13 Looking Ahead
Conductors only stay safe if overcurrent devices open on faults and overloads. Chapter 5 covers fuses and breakers, then zooms out to services, feeders, and branch circuits — how power is arranged from the utility to the last receptacle.