Short answer: Article 300 holds the general rules for every wiring method, and each raceway has its own article, such as 358 for EMT or 352 for PVC. For conduit fill, add the conductor areas from Chapter 9 Table 5 and compare the total with 40% of the raceway area in Table 4 when there are three or more conductors.
Raceway and fill questions are on both parts of the exam. The PSI outline lists Raceways and Cable Trays in the 10-item Wiring Methods area of the Texas Journeyman NEC Knowledge part, and Raceways again in the Calculations part. The Texas Journeyman Practice Pack has step-by-step solutions for 299 calculation questions, each showing the table, the given numbers and every step. US$39 once.
Tsai Electro is an independent learning site. Not affiliated with TDLR, PSI or NFPA. We explain the method in our own words and do not reproduce NEC text. Check every rule and table value in your own 2026 NEC.
How Chapter 3 is organized
Chapter 3 is the wiring-methods chapter. Article 300 comes first and applies to all of them. Article 310 covers conductors (see NEC 310 conductor ampacity). Article 312 and Article 314 cover cabinets and boxes. After that, each cable type and each raceway type has its own article. Texas uses the 2026 NEC for installations and exams from September 1, 2026 (TDLR rule adoption notice, TDLR exam page).
Inside each raceway article, the parts follow the same order: general, installation, then construction. Once you learn where “uses permitted”, “uses not permitted”, “number of conductors”, “bends”, “securing and supporting” and “reaming” sit in one raceway article, you can find them in the others.
Article 300 rules you use every day
| Topic | What it asks in plain words | Where to look |
|---|---|---|
| Conductors together | All conductors of a circuit, including the neutral and equipment grounding conductor, run in the same raceway, cable or trench. | 300.5(B) |
| Protection from damage | Keep cables back from the edge of framing, or protect them with steel plates. | 300.6 |
| Damaged wiring | Wiring and equipment damaged by heat, fire or water have new limits in 2026 on staying in service. | 300.4 |
| Underground | Minimum cover depends on the wiring method and the location. | Table 300.7(A) |
| Supports | Raceways and cables are secured by their own supports, not by ceiling grid wires or other trades’ supports. | Article 300 (support rules) |
| Free conductor at boxes | Leave enough free conductor at each box for splices and devices. | Article 300 (free conductor at boxes) |
| Boxes at splices | Splices and terminations are made in a box or other approved enclosure. | Article 300 (boxes at splices) |
| Complete before pulling | Install the raceway system complete between pull points before you pull wire. | Article 300 (complete raceway before pulling) |
Which raceway article to open
| Raceway | Article | Typical use | Watch for |
|---|---|---|---|
| Electrical metallic tubing (EMT) | 358 | Exposed and concealed indoor runs in commercial buildings | Not where it will suffer severe physical damage. Bends between pull points are limited. |
| Rigid metal conduit (RMC) | 344 | Service masts, outdoor runs, places with heavy physical damage | Threaded fittings; heavy to install. |
| Intermediate metal conduit (IMC) | 342 | Similar to RMC with a thinner wall | Same pattern as RMC. |
| Rigid PVC conduit | 352 | Underground and corrosive areas | Needs expansion fittings where temperature swings move the run. It is nonmetallic, so it does not serve as the equipment grounding path. Run an equipment grounding conductor as the circuit requires. |
| Flexible metal conduit (FMC) | 348 | Short flexible connections to motors and luminaires in dry places | Not in wet locations. |
| Liquidtight flexible metal conduit (LFMC) | 350 | Equipment that vibrates or sits outdoors, like condensers | Length and grounding limits. |
| Electrical nonmetallic tubing (ENT) | 362 | Inside walls and floors of some buildings | Many uses not permitted; check the article. |
The conduit fill method
Conduit fill uses Chapter 9 of the NEC. Table 1 sets the maximum percentage of the raceway area you may fill: 53% for one conductor, 31% for two, and 40% for three or more. Table 4 gives the area of each raceway type and trade size, including a ready-made 40% column. Table 5 gives the area of each insulated conductor type and size. When every conductor is the same size and type, the tables in Informative Annex C give the answer directly.
These are the values used in the examples below. Check each one in your own 2026 NEC.
| Item | Area (square inches) |
|---|---|
| 12 AWG THHN | 0.0133 |
| 10 AWG THHN | 0.0211 |
| 8 AWG THHN | 0.0366 |
| 1/2 inch EMT, 40% | 0.122 |
| 3/4 inch EMT, 40% | 0.213 |
| 1 inch EMT, 40% | 0.346 |
Worked example 1: nine 12 AWG in 1/2 inch EMT
- Conductor area: 9 × 0.0133 = 0.1197 square inches.
- Allowed for 1/2 inch EMT with three or more conductors: 0.122.
- 0.1197 is not more than 0.122, so nine fit.
- A tenth conductor: 10 × 0.0133 = 0.133, which is more than 0.122. Ten do not fit.
Check: 0.122 ÷ 0.0133 = 9.17, so the whole-number answer is 9. Same answer.
Worked example 2: mixed sizes
A run to a small subpanel needs three 8 AWG THHN and one 10 AWG THHN equipment grounding conductor in EMT.
- 8 AWG: 3 × 0.0366 = 0.1098.
- 10 AWG: 1 × 0.0211 = 0.0211.
- Total: 0.1098 + 0.0211 = 0.1309 square inches.
- 1/2 inch EMT allows 0.122. 0.1309 is more, so 1/2 inch is too small.
- 3/4 inch EMT allows 0.213. 0.1309 is less, so 3/4 inch works.
Check: add in a different order. 0.0211 + 0.0366 = 0.0577, plus 0.0366 = 0.0943, plus 0.0366 = 0.1309. Same total.
Worked example 3: how many 10 AWG fit in 3/4 inch EMT?
- 0.213 ÷ 0.0211 = 10.09.
- Round down to whole conductors: 10.
Check: 10 × 0.0211 = 0.211, which is not more than 0.213. 11 × 0.0211 = 0.2321, which is more. So the answer is 10.
Fill is only half the job. More than three current-carrying conductors in one raceway also lowers their ampacity, so a full raceway can force a larger wire size. That adjustment is in Article 310.
Mistakes that fail fill and raceway questions
- Using 40% for one or two conductors. One conductor gets 53% and two get 31%.
- Mixing raceway types. EMT, RMC and PVC of the same trade size have different areas. Use the right part of Table 4.
- Forgetting the grounding conductor. An insulated equipment grounding conductor counts in fill.
- Pulling into an unfinished run. Finish the raceway between pull points first.
- Opening the wrong article. EMT questions are answered in Article 358, not Article 300.
Check yourself
Our own practice questions. Answers below each.
- What is the total area of six 12 AWG THHN? Answer: 6 × 0.0133 = 0.0798 square inches.
- Do six 12 AWG THHN fit in 1/2 inch EMT? Answer: Yes. 0.0798 is less than 0.122.
- Four 8 AWG THHN: 1/2 inch or 3/4 inch EMT? Answer: 4 × 0.0366 = 0.1464. More than 0.122, less than 0.213, so 3/4 inch.
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The code book you will use on the job and in the exam room
NFPA 70, National Electrical Code (NEC), 2026 Edition, softbound. Chapter 9 Tables 4 and 5 and every raceway article are in it. TDLR allows a soft-bound NEC in the exam room, but the exam is written on the 2026 NEC, so bring that edition; loose-leaf, spiral-bound and ring-bound copies are not allowed, and the NEC Handbook is not allowed.
FAQ
What is the maximum conduit fill?
For three or more conductors, 40% of the raceway’s internal area. For one conductor it is 53%, and for two conductors it is 31%. These percentages are in Chapter 9, Table 1 of the NEC.
How many 12 AWG THHN wires fit in 1/2 inch EMT?
Nine. Each 12 AWG THHN is 0.0133 square inches, and 9 × 0.0133 = 0.1197, which is within the 0.122 square inches allowed for 1/2 inch EMT at 40%.
Which NEC article covers EMT?
Article 358. Article 300 has the general rules for all wiring methods, and each raceway type has its own article, such as 344 for rigid metal conduit and 352 for PVC.
Does the ground wire count in conduit fill?
Yes. Equipment grounding conductors count in the fill calculation. Use the insulated conductor area from Table 5 or the bare conductor dimensions from Table 8.
Sources checked October 2026
- TDLR rule adoption notice, 2026 NEC: https://www.tdlr.texas.gov/news/rulemaking/2026/09/01/commission-adopts-rules-12/
- TDLR exam page (open book, soft-bound NEC only): https://www.tdlr.texas.gov/electricians/elecexam.htm
- PSI Candidate Information Bulletin for TDLR (updated 9/15/2026): https://test-takers.psiexams.com/api/content/bulletin/1682
- City of Denison, 2026 NEC significant changes (damaged wiring rules): https://denisontx.gov/DocumentCenter/View/4131/2026-National-Electrical-Code-Significant-Changes
- NFPA 70 (NEC), 2026 edition, Article 300, raceway articles and Chapter 9, read in your own copy: https://www.nfpa.org/codes-and-standards/nfpa-70-standard-development/70
