Counting the Neutral Practice Questions

A. The kind of circuit it belongs to, and in one case the kind of load on that circuit

The section is written entirely in terms of circuits and never mentions a measured value, which is exactly why it works at the design stage before anything has been energized. A neutral carrying 30 amperes can sit outside the count and a neutral carrying almost nothing can sit inside it. Reaching for a meter reading here answers a question the code did not ask.

NEC 2026 310.15(E)

B. As a short positive list of the circuits in which the neutral is current-carrying, followed by an exclusion that picks up everything the list did not take

Find which side of that switch the stem has put you on and the answer follows. Candidates who learned the rule from an older book tend to have the exclusion first in their heads and the list second, and that ordering is what produces the wrong answer. Read the positive list before you read the exclusion.

NEC 2026 310.15(E)

C. It is counted as a current-carrying conductor

The neutral of a two-wire circuit carries exactly what the ungrounded conductor carries, every moment the circuit is energized. Nothing about it is unbalanced, because there is nothing for it to be unbalanced against. This case is missed only by people applying the exclusion as a slogan without checking the list first.

NEC 2026 310.15(E)(1)

D. Counted as a current-carrying conductor

The two ungrounded conductors sit 120 degrees apart rather than opposite each other, so adding two equal currents does not give zero. It gives a current about the same size as either one, which means this neutral carries close to full load current when the phases are perfectly matched. In a raceway it looks identical to a single-phase three-wire circuit, and the only thing separating them is the clause in the stem naming the system.

NEC 2026 310.15(E)(1)

A. Four

Nonlinear loads draw current in pulses, and the third harmonic components from the three phases arrive at the neutral in step with one another instead of canceling, so they add. The neutral of a heavily nonlinear circuit can end up carrying more than any single phase conductor feeding it. All four conductors are counted, which puts this raceway straight into the first adjustment band.

NEC 2026 310.15(E)(1)

B. A four-wire, three-phase wye circuit

The system named in the rule is the whole reach of it, so a single-phase three-wire circuit feeding a room full of computers is not swept in. The physics agrees, because two legs 180 degrees apart put their third harmonics 180 degrees apart as well, and those subtract in the neutral instead of stacking. Naming the system before you read the load type keeps this straight.

NEC 2026 310.15(E)(1)

C. Only circuits that the positive list did not already take

The qualifier sits at the front of the subsection, so the exclusion can never be used to argue a neutral back out of the count on a two-wire circuit or on three wires taken off a wye. Within the circuits it does reach, read the words only and unbalanced as one condition rather than two. A neutral in that position carries current one of the ungrounded conductors is therefore not carrying, so the heat in the raceway has not gone up.

NEC 2026 310.15(E)(2)

D. It is not counted at all

A grounding or bonding conductor carries current during a fault, and a fault is not the sustained thermal condition the ampacity tables were built around. Its size and its insulation make no difference to that. This exclusion is stated separately from the neutral rule and applies wherever the adjustment factors are used.

NEC 2026 310.15(F)

A. The neutral is left out because its current is already accounted for elsewhere in the same circuit, and the grounding conductor is left out because in normal service there is no current to account for

These are two different arguments and questions test the difference. Keeping them separate is what lets you rebuild the whole section from the physics rather than from memory. The adjustment factor exists because bundled conductors cannot get rid of their heat, so a conductor that adds no heat adds nothing to the count.

NEC 2026 310.15(F), 310.15(E)(2)

B. The spares are counted, and the conductors that cannot be simultaneously energized are not

Both of these rules sit in the note printed under the adjustment table rather than in the neutral section, which is why people go looking for them in the wrong place. A spare is one termination away from being a live circuit and the raceway will not know the difference. The non-simultaneous case is the opposite, since two conductors that can never both be hot cannot both add heat.

NEC 2026 Table 310.15(C)(1)

C. Three

The neutral of that feeder carries only the unbalanced current from the other conductors of the same circuit, so the exclusion takes it, and the grounding conductor is outside the count entirely. That leaves the three ungrounded conductors, which is not more than three, so no adjustment factor applies at all. This is the most common item on the subject in any bank and the answer is three.

NEC 2026 310.15(E)(2), 310.15(F)

D. 80 percent

Each circuit contributes two ungrounded conductors and a neutral that the positive list puts into the count, so there are six current-carrying conductors and the grounding conductor is not one of them. Six falls in the band that runs from four through six. Treating those neutrals as excluded gives four, which happens to land in the same band and is the reason this error can survive on a real job.

NEC 2026 310.15(E)(1), Table 310.15(C)(1)

A. 80 percent

The nonlinear trigger brings the neutral into the count, so there are four current-carrying conductors and the raceway crosses the threshold that a linear version of the same circuit would not. Four sits in the first band. One word in the stem moves this circuit from no adjustment at all to a 20 percent reduction, which is why the load description is worth reading twice.

NEC 2026 310.15(E)(1), Table 310.15(C)(1)

B. 70 percent

Each circuit contributes three ungrounded conductors and a counted neutral, so there are eight current-carrying conductors. Eight falls in the band that runs from seven through nine. The bands step down in blocks rather than smoothly, so a miscount near a boundary changes the conductor size and a miscount in the middle of a band changes nothing.

NEC 2026 Table 310.15(C)(1)

C. 4 through 6 at 80 percent, 7 through 9 at 70 percent, 10 through 20 at 50 percent

The drop from the second band to the third is the sharp one, because a raceway with ten conductors in it is a very different thermal problem from one with nine. Above 20 the factors continue at 45, 40 and 35 percent. You will have the table on the exam, so the value of knowing the shape is speed rather than recall.

NEC 2026 Table 310.15(C)(1)

D. 40.04 amperes

Start at 55 amperes from the 90 degree column, multiply by the 0.91 ambient correction for the 90 degree column at 36 to 40 degrees C, then by the 0.80 adjustment for five conductors. That gives 55 times 0.91 times 0.80, or 40.04 amperes. The 44 ampere answer applies the adjustment and forgets the ambient correction, which is the most common miss on a two-factor problem.

NEC 2026 310.15(B), 310.15(C)(1), Table 310.16

A. 32 amperes

Neither neutral is counted, so the raceway holds six current-carrying conductors and the adjustment factor is 0.80. The 90 degree column gives 40 amperes, and 40 times 0.80 is 32 amperes, which is below the 35 ampere termination limit read from the 75 degree column. Starting from the 75 degree column instead of the 90 degree column produces the 28 ampere answer.

NEC 2026 310.15(E)(2), 310.15(C)(1), 110.14(C), Table 310.16

B. 52.5 amperes

Each of those circuits puts two ungrounded conductors and a counted neutral into the raceway, so there are nine current-carrying conductors and the factor is 0.70. The 90 degree column gives 75 amperes, and 75 times 0.70 is 52.5 amperes. Nine is the last number in that band, and one more counted conductor drops the factor to 0.50 and the result to 37.5 amperes.

NEC 2026 310.15(E)(1), 310.15(C)(1), Table 310.16

C. 20 amperes

The small conductor rule sets a hard ceiling for 12 AWG copper and it applies after the correction and adjustment factors have been worked out. So the calculation gives you an ampacity of 24 amperes and the device still stops at 20. The rule is written to bite exactly here, where the arithmetic tempts you into a larger device.

NEC 2026 240.4(D)

D. Where more than three current-carrying conductors are installed without maintaining spacing for a continuous length longer than 24 inches

Both halves of that condition matter, the count and the length. The same rule reaches single conductors and multiconductor cables that are not in a raceway at all, where they are bundled without spacing over that length. A short run through a nipple is the case the length condition was written for.

NEC 2026 310.15(C)(1)

A. None, because the adjustment factors do not apply to a raceway not exceeding 24 inches

A short raceway does not hold heat the way a long one does, so the code releases it outright rather than softening the factor. The relief is stated as a length and nothing else, and 24 inches is the same figure that appears in the general condition for applying the factors. Reaching for a reduced factor rather than no factor is the trap the option list is built around.

NEC 2026 310.15(C)(1)

B. Nine

The section says outright that each current-carrying conductor of a paralleled set is counted as a current-carrying conductor. Paralleling divides the current but not the heat, since every conductor in the raceway still has its own share to get rid of. Counting a parallel set as one conductor per phase is a shortcut that puts the answer three bands too high.

NEC 2026 310.15(C)(1)

C. Seven, every conductor in the raceway

Fill is about physical space, so a conductor takes up room whatever it is doing electrically and nothing is excluded. The derating count and the fill count are two different numbers taken off the same drawing. A well-built item hands you one raceway and asks for both, and the candidate carrying one number in their head answers half of it correctly.

NEC 2026 Chapter 9 Table 1

D. Nothing, since the feeder neutral load calculation and the current-carrying count are separate rules in different chapters

One rule decides how large the neutral conductor has to be, and the other decides whether that conductor adds to the heat in the raceway. Neither answers the other, and an item can hand you both in one stem. Naming which question you are answering before you open a table is what keeps them apart.

NEC 2026 120.61, 310.15(E)

A. It is the code's own phrase and a judgment rather than a stated percentage, so an exam stem will say outright that the condition is met

No percentage is printed anywhere in the section, and an item writer knows nobody could infer it from a list of equipment. What makes a load nonlinear is a switching supply in front of it, so electronic ballasts, LED drivers, computer power supplies and variable frequency drives all qualify while a resistance heater does not. Answers that supply a threshold are supplying something the code does not.

NEC 2026 310.15(E)(1)