Conduit Fill Practice Questions

A. One conductor is the most generous and two conductors is the tightest

The rows do not run in the order people expect. One conductor gets the most room, two conductors get the least, and over two settles back between them. The reason the two conductor figure is the lowest is mechanical rather than electrical, since two round conductors in a round pipe jam against each other in a way that three or more do not. Read the row off the conductor count and take the percentage out of the book in front of you.

NEC 2026 Chapter 9 Table 1

B. The two conductor row

A multiconductor cable is treated as a single conductor for fill, so two cables is the two conductor case and not the six conductor case. That takes you to the lowest of the three percentages rather than the highest, which can move the answer by two trade sizes. An item that names a cable type rather than a wire type is usually asking exactly this.

NEC 2026 Chapter 9 Table 1 Note 9

C. The major diameter of the ellipse, treated as a circle diameter

The note is deliberately conservative, since the cable has to pass through the pipe in whatever orientation it lands in and the widest dimension is what has to fit. Averaging the two diameters looks reasonable and produces an area that is too small. Adding up the conductors inside defeats the whole point of counting the cable as one.

NEC 2026 Chapter 9 Table 1 Note 9

A. No, the fill is calculated on the individual conductors

The note that makes a cable count as one conductor closes with a sentence excluding assemblies of single insulated conductors that have no overall covering. Without a jacket there is no cable, so each conductor is counted on its own out of Table 5. Taping a bundle together on the job does not manufacture a cable.

NEC 2026 Chapter 9 Table 1 Note 9

D. No, the table applies only to complete conduit or tubing systems

One of the notes says in as many words that the table covers complete conduit or tubing systems and is not aimed at sections used to protect exposed wiring and cable from damage. So a sleeve over a cable coming out of the ground is not a fill problem. It is still a physical protection question and the sleeve still has to be an approved method.

NEC 2026 Chapter 9 Table 1 Note 2

B. The nipple column, which Table 4 already prints beside the others

A nipple not over 24 inches installed between enclosures is permitted a larger share than an ordinary raceway, and Table 4 already prints that column beside the others, so the nipple case is a column change rather than a calculation. Under time pressure people work the larger share out of the total area by hand while the answer sits one column over. The single conductor column belongs to a pull of one conductor rather than to a short length, and the total area column is never the permitted area.

NEC 2026 Chapter 9 Table 1 Note 4, Chapter 9 Table 4

A. A maximum length of 24 inches, and installation between boxes, cabinets and similar enclosures

Length and location both have to be true. Over 24 inches it is an ordinary raceway, and a short piece that does not run between enclosures is an ordinary raceway as well. The note measures the nipple without its connectors, which is worth noticing on a piece cut close to the limit.

NEC 2026 Chapter 9 Table 1 Note 4

B. 10

The division gives 9.88, and the rounding note says the next higher whole number is used where all the conductors are the same size and the calculation lands on a decimal of 0.8 or larger. So the answer is 10 rather than the 9 that truncation would give. Throwing the decimal away is right most of the time, which is exactly why this case is worth checking every time.

NEC 2026 Chapter 9 Table 1 Note 7

C. All of the conductors are of the same size, meaning the same total cross-sectional area including insulation

The condition is as important as the note itself. Same size means same area with the insulation counted, so two conductors of the same AWG in different insulation types do not satisfy it either. A candidate who has just learned the 0.8 rule and applies it to every pull has traded one wrong answer for another.

NEC 2026 Chapter 9 Table 1 Note 7

B. The rounding note and the finished counts in Informative Annex C

Both shortcuts exist for the all one size case and both stop at the same boundary, which is not a coincidence since the annex was built by running the same notes. Mixing sizes puts you back on the long method with the decimal truncated. Items mix sizes on purpose to shut that door, so check for uniformity before reaching for either one.

NEC 2026 Chapter 9 Table 1 Notes 6 and 7, Informative Annex C

D. Table 8

Table 5 covers insulated conductors and fixture wires, so a bare conductor is not in it. One of the notes permits the bare conductor dimensions from Table 8, which is the conductor properties table. Table 4 is raceway areas and Table 5A is compact stranded building wire, so both are the wrong kind of table entirely.

NEC 2026 Chapter 9 Table 1 Note 8, Chapter 9 Table 8

A. Taking a percentage column on the right row, and taking the total area column on the wrong row

One is a column error and one is a row error, and both hand you a number that reads like a raceway area. Taking a percentage figure instead of the total area is the most common column slip on this table, and taking a total area one trade size up or down is the row slip. Check the row and the column heading before you write the number down, and check that you are in the right raceway block as well, because two raceway types of the same trade size do not have the same internal area.

NEC 2026 Chapter 9 Table 4

A. THHN only

Four at 0.0507 is 0.2028, which is inside the permitted area, and four at 0.0590 is 0.2360, which is over it. Insulation thickness differs by type, so the same wire size covers a different area depending on what is wrapped around it, and on a full pull that gap is wide enough to change the trade size. Find the insulation type block in the table first and the size inside it second, rather than reading a size off the first block your eye lands on.

NEC 2026 Chapter 9 Table 5, Chapter 9 Table 1

B. Total each size group out of Table 5, add the two totals, and take the over two conductor row of Table 1

Nine of one size and three of another is a mixed pull, so each group is totaled on its own and the two totals are added, and there are more than two conductors so the over two row governs. Only then does Table 4 come into it, and you read down the column that row picked until you reach the first trade size whose figure equals or exceeds the total. Annex C is closed the moment the sizes stop matching, and averaging the two areas is not a method the notes offer.

NEC 2026 Chapter 9 Table 1, Chapter 9 Table 4, Chapter 9 Table 5

B. 16

The division gives 16.02, and a decimal of 0.02 is nowhere near the rounding threshold, so the answer truncates to 16. The finished count table in the informative annex prints the same figure, which is a useful cross check when the arithmetic is close. The largest option is the same conductor in a 1 inch raceway.

NEC 2026 Chapter 9 Table 1, Chapter 9 Table 4, Chapter 9 Table 5

A. 5

The division gives 5.78. That decimal is under 0.8, so the rounding note does not reach it and the count truncates to 5. Getting close to the threshold without crossing it is the point of the item, because a candidate who has memorized the rounding rule as round up will read 5.78 as 6 and be one conductor over the limit.

NEC 2026 Chapter 9 Table 1 Note 7, Chapter 9 Table 4, Chapter 9 Table 5

C. Table 5

Three tables carry the method between them. Table 1 sets the percentage, Table 5 gives the conductor areas, and Table 4 gives the raceway areas with the percentages already worked out. Table 8 is conductor properties, which is where resistance, circular mils and bare conductor dimensions live.

NEC 2026 Chapter 9 Table 5

D. By article, with each raceway type in its own block

Electrical metallic tubing sits under its own article number and rigid metal conduit under another, so finding the right block is a navigation task before it is a lookup. Two raceway types of the same trade size have different internal areas, and landing in the wrong block gives a number that looks entirely reasonable. That is where the time goes on this subject.

NEC 2026 Chapter 9 Table 4

D. The conductors are all of the same size and type

The annex was built by running the Chapter 9 notes on one size and one type at a time, so it answers only that case. Add a smaller grounding conductor or a second phase conductor size and the annex is closed and the long method is back. The uniformity test that governs the annex is the same one that governs the rounding note.

NEC 2026 Informative Annex C, Chapter 9 Table 1 Note 1

A. It sends you to the percentage fill in Chapter 9 Table 1

The number of conductors section in each raceway article is one sentence long and it points at Chapter 9 Table 1. The rigid polyvinyl chloride conduit article says the same thing in the same words. That is why the method is learned once and applied to every raceway type rather than learned article by article.

NEC 2026 358.22, 352.22

C. Yes where the cable article does not prohibit it, and the number is held to the same Chapter 9 Table 1 percentages

The second paragraph of that section permits cables where the cable's own article does not bar the use, and then holds the count to the same percentages. So the answer needs two lookups, one in the cable article and one in Chapter 9. Remember that each cable counts as a single conductor when you take that count.

NEC 2026 358.22, Chapter 9 Table 1 Note 9

A. 20 percent

An auxiliary gutter is not a conduit and the Chapter 9 percentages do not reach it. Its own article sets 20 percent for both the sheet metal and the nonmetallic versions, which is far tighter than anything in the conduit table. An item that swaps a gutter for a conduit in the stem is testing whether you noticed the enclosure changed.

NEC 2026 366.22

B. Actual dimensions, or Table 5 and Table 5A for the conductors together with Table 4 for the raceway

There is no shortcut for a mixed pull and the tables do not offer one, so each group is totaled separately and the totals are added. The note also permits actual dimensions where they are known, which matters when a manufacturer publishes a smaller figure than the table's worst case. Annex C is closed the moment the sizes stop matching.

NEC 2026 Chapter 9 Table 1 Note 6

D. Table 5A

Table 5 groups solid and round concentric-lay-stranded values together and is built on a worst case, while compact stranded values sit in their own table. A note says that where the actual conductor diameter and area are known, those figures are permitted instead. On a large aluminum pull the difference between the two tables can be a whole trade size.

NEC 2026 Chapter 9 Table 5A, Chapter 9 Table 1 Note 10

C. From its actual dimensions, since it is not one of the conductors the Chapter 9 tables list

One of the notes handles everything the Chapter 9 tables do not list, naming multiconductor cables and optical fiber cables and sending you to their actual dimensions. So a manufacturer catalog page becomes part of the calculation. Leaving the cable out is the tempting answer because it carries no current, and it is wrong for the same reason a grounding conductor still counts.

NEC 2026 Chapter 9 Table 1 Note 5