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5.6 Conduit Fill: Chapter 9 Tables and Annex C

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Alaska Journeyman Electrician Study Guide Exam

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1 Chapter 1: Alaska Certificates of Fitness, Law & Exam Logistics

1.1 The Alaska Certificate of Fitness System 1.2 Journeyman Eligibility: 8,000 Hours and How Alaska Counts Them 1.3 Trainee, Residential Wireman, Lineman, Provisional & Reciprocal Certificates 1.4 The Journeyman Examination: Format, Scheduling, Open-Book Rules & Retakes 1.5 Adopted Codes, Fees, Renewal, Inspection & Enforcement

2 Chapter 2: Using the 2020 NEC

2.1 Article 90: Purpose, Scope, Arrangement & Enforcement 2.2 Navigating the Code Book: Structure, Index & Tabbing Strategy 2.3 Article 100 Definitions You Must Know Cold 2.4 Electrical Theory for the Exam: Ohm's Law, Power & Three-Phase

3 Chapter 3: General Requirements — Article 110

3.1 Approval, Listing, Interrupting Rating & Terminations 3.2 Temperature Limitations of Terminations — 110.14(C) 3.3 Working Space, Access, Egress & Illumination — 110.26(A) through (D) 3.4 Dedicated Equipment Space, Guarding & Over-1000-Volt Installations

4 Chapter 4: Conductors and Ampacity — Article 310

4.1 Conductor Types, Insulation Markings & Table 310.16 4.2 Ambient Temperature Correction and Alaska's Cold 4.3 Adjustment for More Than Three Current-Carrying Conductors 4.4 Putting It Together: Full Conductor-Sizing Problems 4.5 Parallel Conductors, Dwelling Service Sizing & Conditions of Use

5 Chapter 5: Wiring Methods and Materials — NEC Chapter 3

5.1 Article 300 General Requirements and Underground Cover 5.2 Thermal Movement: Expansion Fittings and Table 352.44 5.3 Boxes and Enclosures: Box Fill and Pull Box Sizing 5.4 Cable Assemblies: NM, MC, AC, SE, UF and TC 5.5 Raceways: RMC, IMC, EMT, FMC, LFMC, PVC and ENT 5.6 Conduit Fill: Chapter 9 Tables and Annex C 5.7 Cable Trays, Wireways, Busways, Gutters and Surface Raceways

6 Chapter 6: Branch Circuits and Feeders

6.1 Branch-Circuit Ratings, Conductor Sizing & Multiwire Circuits 6.2 Required Outlets and Receptacle Spacing in Dwellings 6.3 GFCI Protection — Article 210.8 6.4 AFCI Protection and Receptacle Requirements 6.5 Feeders and Outside Branch Circuits — Articles 215 and 225 6.6 Grounded Conductor Identification, Switches & Panelboards

7 Chapter 7: Overcurrent Protection — Articles 240 and 242

7.1 Article 240 Fundamentals: Ratings, Locations & Conductor Protection 7.2 Feeder Tap Rules — 240.21(B) 7.3 Transformer Secondary Conductors — 240.21(C) 7.4 Fuses, Circuit Breakers, Series Ratings & Article 242 Surge Protection

8 Chapter 8: Services and Load Calculations

8.1 Service Conductors, Clearances and Service Equipment 8.2 Service Disconnects, the 2020 Rule Change, SPDs and Service GFPE 8.3 Article 220 Part II: General Lighting, Receptacles and Demand Factors 8.4 The Standard Dwelling Calculation — Article 220 Part III 8.5 Optional Dwelling and Multifamily Calculations 8.6 Commercial and Industrial Load Calculations 8.7 Neutral Load Calculations and Harmonics — 220.61

9 Chapter 9: Grounding and Bonding — Article 250

9.1 System Grounding, 250.24 and the Main Bonding Jumper 9.2 The Grounding Electrode System — 250.50 through 250.53 9.3 Grounding Electrode Conductor Sizing and Installation 9.4 Bonding: Services, Metal Piping, Structural Metal and Other Systems 9.5 Equipment Grounding Conductors: Types, Sizing and Continuity 9.6 Separately Derived Systems and Separate Buildings 9.7 Ground-Fault Protection of Equipment and Grounding of Specific Equipment

10 Chapter 10: Equipment for General Use — NEC Chapter 4

10.1 Flexible Cords, Cables and Fixture Wires 10.2 Switches, Receptacles and Industrial Control Panels 10.3 Luminaires, Lampholders and Recessed Installations 10.4 Appliances and Fixed Electric Space Heating 10.5 Deicing, Snow Melting, Pipeline and Vessel Heating 10.6 Motors Part I: Full-Load Current, Conductors and Overload Protection 10.7 Motors Part II: Short-Circuit Protection, Controllers, Disconnects and HVAC

11 Chapter 11: Transformers, Generators and Special Occupancies

11.1 Transformers — Article 450 11.2 Generators, Storage Batteries and Energy Storage Systems 11.3 Hazardous (Classified) Locations — Articles 500 through 506 11.4 Garages, Hangars, Fuel Dispensing, Bulk Storage and Spray Application 11.5 Health Care Facilities — Article 517 11.6 Agricultural Buildings, Manufactured Homes, RV Parks and Marinas 11.7 Assembly, Theaters, Carnivals, Temporary Installations and Pools

12 Chapter 12: Special Equipment, Special Conditions and Exam Strategy

12.1 Signs, Cranes, Elevators, Electric Vehicle Charging and Welders 12.2 Solar Photovoltaic, Interconnection and Stand-Alone Systems 12.3 Wind Electric Systems and Fire Pumps 12.4 Emergency, Legally Required Standby, Optional Standby and COPS 12.5 Class 1, 2 and 3 Circuits, Fire Alarm, Optical Fiber and Communications 12.6 Cold-Climate Practice in Alaska: Code Basis and Engineering Judgment 12.7 Exam-Day Strategy: Navigation, Calculation Workflow and Time Management

5.6 Conduit Fill: Chapter 9 Tables and Annex C

Key Takeaways Explain This Topic AI

Chapter 9 Table 1 permits 53 percent fill for one conductor, 31 percent for two conductors, and 40 percent for over two conductors in a raceway.

Chapter 9 Table 1 Note 4 permits nipples not exceeding 24 inches between boxes or cabinets to be filled to 60 percent, with no ampacity adjustment required.

Chapter 9 Table 4 gives the interior cross-sectional area of every raceway type at each permitted fill percentage; Table 5 gives the approximate area of each insulated conductor by type and size.

Chapter 9 Table 1 Note 7 requires rounding up to the next whole number where the calculation results in 0.8 or larger, and Note 8 requires bare conductors to use Table 8 dimensions.

Informative Annex C provides precomputed conduit and tubing fill tables valid only where all conductors in the raceway are the same size and insulation type.

Last updated: August 2026

Why Fill Is Limited

Raceway fill limits exist for two reasons: heat dissipation and pulling tension . A raceway packed with conductors runs hotter and requires more force to pull, damaging insulation. The percentages in Chapter 9 Table 1 are derived from an assumption of a jam ratio and pulling geometry, not from any thermal calculation — the thermal side is handled separately by the 310.15(C)(1) adjustment factors.

Chapter 9, Table 1 — Percent of Cross Section

  • Number of conductors Maximum fill
  • 1 53 percent
  • 2 31 percent
  • Over 2 40 percent

The two-conductor case being the tightest looks counterintuitive but comes from the geometry of two circles inside a circle — the wasted space is greatest with two.

The Notes to Table 1

The notes are as enforceable as the table:

Note 1. See Informative Annex C for the maximum number of conductors and fixture wires, all of the same size and insulation type, permitted in trade sizes of the applicable conduit or tubing.

Note 2. Table 1 applies only to complete conduit or tubing systems and is not intended to apply to sections used to protect exposed wiring from physical damage.

Note 4. Where conduit or tubing nipples having a maximum length not to exceed 600 mm (24 in.) are installed between boxes, cabinets, and similar enclosures, the nipples shall be permitted to be filled to 60 percent of their total cross-sectional area, and 310.15(C)(1) adjustment factors need not apply to this condition.

Note 6. For conductors not included in Chapter 9, such as multiconductor cables and optical fiber cables, the actual dimensions shall be used.

Note 7. When calculating the maximum number of conductors permitted in a conduit or tubing, all of the same size (total cross-sectional area including insulation), the next higher whole number shall be used to determine the number of conductors permitted when the calculation results in a decimal of 0.8 or larger .

Note 8. Where bare conductors are permitted, the dimensions for bare conductors in Table 8 shall be used.

Note 9. A multiconductor cable or flexible cord of two or more conductors shall be treated as a single conductor for calculating percentage conduit fill area. For cables that have elliptical cross sections, the cross-sectional area calculation shall be based on using the major diameter of the ellipse as a circle diameter .

Note 9 is a favorite exam item: a single 12/3 MC cable pulled through a conduit is one conductor for fill, using the major diameter of the ellipse.

The Two-Table Method

For conductors of mixed sizes or types , work in three steps: 1. From Chapter 9 TABLE 5, look up the approximate area (sq in)

of each conductor by insulation type and size. Multiply by quantity.

2. Sum all conductor areas, including any equipment grounding conductor.

  • 3. From Chapter 9 TABLE 4, find the raceway type and read down the
  • column for the applicable fill percentage (usually the Over 2 Wires 40%

column) until you find a trade size whose area equals or exceeds your sum.

Table 5 Values to Recognize

Approximate area in square inches for THHN/THWN/THWN-2:

  • Size Area (sq in)
  • 14 AWG 0.0097
  • 12 AWG 0.0133
  • 10 AWG 0.0211
  • 8 AWG 0.0366
  • 6 AWG 0.0507
  • 4 AWG 0.0824
  • 3 AWG 0.0973
  • 2 AWG 0.1158
  • 1 AWG 0.1562
  • 1/0 AWG 0.1855
  • 2/0 AWG 0.2223
  • 3/0 AWG 0.2679
  • 4/0 AWG 0.3237

Note that XHHW and THW have larger areas than THHN at the same AWG because the insulation is thicker. Always match the insulation type in the question to the correct Table 5 column — substituting THHN areas into an XHHW problem is the most common error.

Table 4 Values to Recognize — EMT, 40 Percent Column

  • Trade size 40 percent area (sq in)
  • 1/2 0.122
  • 3/4 0.213
  • 1 0.346
  • 1-1/4 0.598
  • 1-1/2 0.814
  • 2 1.342
  • 2-1/2 2.343
  • 3 3.538

Each raceway type has its own Table 4 section. EMT, RMC, IMC, PVC Schedule 40, and PVC Schedule 80 all have different interior areas at the same trade size — Schedule 80 is noticeably smaller because of its thicker wall.

Worked Example 1 — Mixed Sizes

How large an EMT is needed for three 2 AWG THHN copper conductors, one 4 AWG THHN neutral, and one 8 AWG THHN equipment grounding conductor? 3 x 2 AWG THHN @ 0.1158 = 0.3474 sq in

  • 1 x 4 AWG THHN @ 0.0824 = 0.0824 sq in
  • 1 x 8 AWG THHN @ 0.0366 = 0.0366 sq in
  • -----------
  • Total conductor area 0.4664 sq in

Five conductors means "over 2" and therefore the 40 percent column. From Table 4, EMT:

1-1/4 in at 0.598 sq in — 0.4664 fits .

1 in at 0.346 sq in — too small.

Answer: trade size 1-1/4 EMT. Note that the equipment grounding conductor is counted in the fill calculation even though it is not counted as a current-carrying conductor for ampacity adjustment. Those two counts are different and both appear on exams.

Worked Example 2 — Same Size, Use Annex C

How many 12 AWG THHN conductors are permitted in trade size 3/4 EMT?

All conductors are the same size and type, so Informative Annex C, Table C.1 applies directly: 16 conductors .

  • Verify by the long method: Table 4, 3/4 EMT, 40 percent = 0.213 sq in
  • Table 5, 12 AWG THHN = 0.0133 sq in
  • 0.213 / 0.0133 = 16.02 conductors

16.02 truncates to 16. Note that Note 7's round-up applies only at 0.8 or larger — 16.02 does not round to 17.

A case where Note 7 does apply: if the calculation had produced 16.85, the answer would be 17 conductors.

Worked Example 3 — Nipple

Eight 6 AWG THHN conductors pass through an 18-inch RMC nipple between two enclosures. What trade size is required? 8 x 6 AWG THHN @ 0.0507 = 0.4056 sq in

Note 4 permits 60 percent fill for a nipple 24 in or less.

Table 4, RMC, 60 percent column:

  • trade size 1 = 0.531 sq in -> 0.4056 fits
  • trade size 3/4 = 0.307 sq in -> too small

Trade size 1 RMC. And under Note 4, the eight conductors need no ampacity adjustment even though eight exceeds three.

Multiconductor Cables in Raceway

Under Note 9, treat each cable as a single conductor , using its overall diameter. For an elliptical cable, use the major diameter as the circle diameter and compute the area as pi times radius squared. Because you are computing the area of a circle enclosing a flat cable, the number is conservative — that is deliberate.

With one cable in the raceway you may use the 53 percent column; with two , the 31 percent column; with three or more, 40 percent.

What Annex C Cannot Do

Annex C is informative under 90.5(D), and its tables are precomputed for the case where all conductors are the same size and insulation type . It cannot be used where:

  • conductor sizes are mixed;
  • insulation types are mixed;
  • multiconductor cables are being pulled;
  • the raceway is a nipple being filled to 60 percent;

bare conductors using Table 8 dimensions are present in the count.

In all of those cases, return to Tables 1, 4, 5, and 8.

Existing Raceways and Physical Damage Sleeves

Table 1, Note 2 exempts short sections of raceway used solely to protect exposed wiring from physical damage from the fill limits. A sleeve over NM cable where it passes through a garage wall is not a complete conduit system and is not subject to the percentages — though the sleeve must still be sized so the cable is not damaged during installation.