Power and Volt-Amperes Practice Questions

D. The total ampere ratings of the units

A driver draws more current than the lamp wattage implies, and the conductor heats on current rather than on useful light. So the section names the ampere ratings of the units and says so for ballasts, transformers, autotransformers and drivers alike. An item that hands you a lamp wattage and a unit ampere rating in the same stem is testing this one line.

NEC 2026 120.11(B)

B. 6,000 volt-amperes

Volt-amperes is the voltage across the load times the current through it, so 240 times 25 gives 6,000 and the power factor never enters. The 4,800 figure is the watts, which is the useful work rather than what the conductor carries, and 7,500 comes from dividing by the power factor a second time after the current already reflects it. Take the current the stem gives you and stop.

NEC 2026 120.40

A. About 33.3 kilovolt-amperes

The line form is the line-to-line voltage times the line current times the square root of three, so 480 times 40 times 1.732 gives about 33,300 volt-amperes. Leaving the square root out gives 19.2 kilovolt-amperes and multiplying by three instead gives 57.6, and both of those wrong answers appear on paper often enough to be worth recognizing. The word line is doing the work in that formula.

NEC 2026 120.40

C. 173 amperes

Divide the volt-amperes by the square root of three times 208, which is about 360, and you get 173.2 amperes. Load calculations may be rounded to the nearest whole ampere with decimal fractions below 0.5 dropped, so 173 stands. The 300 comes from dividing by 208 alone, the 100 from dividing by three times 208, and the 520 from using the 120-volt figure, which is a phase voltage and not what this formula takes.

NEC 2026 120.5(A), 120.5(B)

D. Low by a factor of about 1.73

The three-phase line formula takes the line-to-line voltage, and on a wye system the line-to-line figure is the phase figure times the square root of three. The nominal designation prints both numbers, which is why using the wrong half of it is so easy. Written from the phase side the same quantity is three times the phase voltage times the phase current, with no square root anywhere, so two forms give one answer and mixing them gives you the factor of 1.73.

NEC 2026 120.5(A)

A. A load based on the ampere rating of the appliance or load served

The subsection sends you to the equipment rather than to a per-outlet figure, so read the rating on the appliance before you reach for a table number. The 180 volt-ampere figure belongs to general-use receptacle outlets and to outlets the section does not otherwise cover. The 1,500 figure is the small-appliance and laundry circuit number from the feeder and service part, and it does not belong at a single appliance outlet.

NEC 2026 120.14(A), 120.14(K)

B. 6,000 volt-amperes

The branch-circuit unit load for a dwelling is 3 volt-amperes per square foot, so 2,000 times 3 gives 6,000 volt-amperes. That figure exists to work out how many circuits the dwelling needs. A different and smaller figure carries the same idea into the feeder and service calculation, so read which of the two the stem is asking for before you multiply.

NEC 2026 120.13, 120.5(C)

C. 4,000 volt-amperes

The feeder and service unit load is 2 volt-amperes per square foot, so 2,000 times 2 gives 4,000 volt-amperes. It is deliberately lower than the branch-circuit figure because it feeds a calculation that already carries demand factors and diversity. Using one where the other belongs produces a plausible wrong answer, which is exactly why the two sections sit in different parts of the article.

NEC 2026 120.41

D. 11,700 volt-amperes

The table lists an office at 1.3 volt-amperes per square foot, so 9,000 times 1.3 gives 11,700. The wrong answers come from the warehouse row at 1.2, the retail row at 1.9, and the dwelling branch-circuit figure of 3, all of which are real numbers in the wrong place. A footnote to the table puts banks in the office row, so read the footnotes before you pick a row.

NEC 2026 120.42(A), Table 120.42(A)

A. 540 volt-amperes

The general figure is 180 volt-amperes for each single or multiple receptacle on one yoke, but a single assembly of four or more receptacles is calculated at 90 volt-amperes per receptacle instead. Six times 90 gives 540. Taking the 180 figure per receptacle gives 1,080, which is the trap, and treating the whole assembly as one yoke gives 180.

NEC 2026 120.14(I)

B. 3,600 volt-amperes

The show window figure is 200 volt-amperes per linear foot, so 18 times 200 gives 3,600. The section gives a choice between this method and the unit load per outlet, and an item can hand you an outlet count as well to see which you reach for. Note the 200 figure belongs to show windows and nowhere else in the section.

NEC 2026 120.14(G)

C. 1,080 volt-amperes

Where simultaneous use is unlikely, each 5 feet or fraction of a continuous length counts as one outlet of not less than 180 volt-amperes, so 30 feet is six outlets and six times 180 gives 1,080. Where simultaneous use is likely, each foot counts instead and the same run comes to 5,400. One sentence in the stem moves the answer by a factor of five, and the rule does not apply in dwelling units or hotel and motel guest rooms at all.

NEC 2026 120.14(H)

D. The full-load current table value of 14 amperes, since horsepower describes shaft output and the terminal current is larger by the efficiency and again by the power factor

Three assumptions sit between a horsepower rating and an ampere figure, which is why the code refuses the arithmetic and names the tables instead. The table values are used for conductor ampacity, switch ratings and branch-circuit short-circuit and ground-fault protection, in place of the nameplate. Nameplate current has its own job in this article, and it is the overload calculation rather than the conductor.

NEC 2026 430.6(A), Table 430.250

A. The input is the larger figure, and the ratio of about 85 percent is the efficiency

Five horsepower is 3,730 watts at the shaft, and 3,730 divided by 4,400 is about 0.85, so input exceeds output by the losses. Efficiency is output over input, so an answer above 100 percent means the two were divided the wrong way round. This is a second reason the code sends motor conductor sizing to a table rather than letting you work from power.

NEC 2026 430.6(A)

B. 40.5 amperes

Capacitor circuit conductors are sized at not less than 135 percent of the rated current of the capacitor, so 30 times 1.35 gives 40.5 amperes. The 37.5 figure comes from applying 125 percent, which is the multiplier used elsewhere and not here. Conductors connecting a capacitor to motor terminals or to motor circuit conductors carry a second floor as well, at one third the ampacity of the motor circuit conductors.

NEC 2026 460.8

C. 30 amperes

Four hours clears the three hour mark in the definition, so this is a continuous load and the conductor is sized at 125 percent of it. Twenty-four times 1.25 gives 30 amperes. The 27.6 figure comes from 115 percent, which belongs to a motor overload calculation and not here, and 24 ignores the multiplier entirely.

NEC 2026 210.19(A), Article 100

D. A load where the maximum current is expected to continue for 3 hours or more

Three hours is the whole test and it is about the maximum current rather than about whether the equipment is switched on. The definition sits in Article 100 rather than in the branch-circuit article, which is where candidates go looking for it. Every 125 percent multiplier in a load calculation traces back to this one sentence.

NEC 2026 Article 100

A. Not less than 125 percent of the largest motor load plus the sum of the other loads

Only the largest motor load takes the multiplier, because the point of it is starting current in one machine rather than a general safety margin. Applying 125 percent to everything oversizes the circuit and applying nothing undersizes it. Where a circuit supplies only motor loads the conductor sizing rule in the motor article governs instead.

NEC 2026 120.11(A), 430.24

B. 9,000 volt-amperes

Office buildings take the larger of two figures, so work both. Forty outlets at 180 volt-amperes gives 7,200, and 1 volt-ampere per square foot gives 9,000, so the area figure governs here. Change the outlet count to 60 and the other figure wins, which is why an item on this always gives you both facts and expects you to compare rather than pick.

NEC 2026 120.14(J), 120.14(I)

C. 2,080 square feet and 4,160 volt-amperes

The floor area for each floor is taken from the outside dimensions, so 26 times 40 is 1,040 per floor and both floors count, giving 2,080 square feet. At the feeder and service unit load of 2 volt-amperes per square foot that is 4,160. The 6,240 answer uses the branch-circuit figure of 3 instead, and the two answers with 1,040 have quietly forgotten the second floor.

NEC 2026 120.5(C), 120.41

A. A table of references pointing at the article and part that holds the rule, in this case Article 440 Part IV

The article carries a pointer table for specific-purpose calculations that amend or supplement it, and reading that table is faster than hunting. The same table sends capacitors, fixed electric space heating, several kinds of motor calculation and storage-type water heaters to their own articles. Knowing the table exists turns a two minute hunt into a ten second lookup.

NEC 2026 120.4, Table 120.4

D. Not less than the sum of the loads on the branch circuits supplied, after any applicable demand factors have been applied

The general section says the calculated load is built up from the branch circuits and then allowed to come down by whatever demand factors the later parts permit. Demand factors are the whole reason a service is smaller than the sum of everything connected to it. The other three answers each describe a rule that exists somewhere in the code but not here.

NEC 2026 120.40

B. About 42.5 amperes

Watts is volt-amperes times power factor, so run it backward: 30,000 divided by 0.85 gives about 35,300 volt-amperes, and dividing that by the square root of three times 480 gives about 42.5 amperes. The 36.1 answer is what the same load would draw at unity power factor, which is the figure a candidate gets by ignoring the power factor entirely. Same useful work, more current, larger conductor.

NEC 2026 120.40

C. General-use receptacle outlets of 20-ampere rating or less including those on the required bathroom and garage circuits, the outdoor receptacle outlets for balconies, decks and porches, and the required lighting outlets

The section exists so you do not add outlet-by-outlet loads on top of a unit load that already includes them, and it names the three groups it swallows. It is the hotel and motel counterpart of the sentence that does the same job for dwelling units. An item on this is really asking whether you double counted.

NEC 2026 120.44, 120.41

A. 35 amperes

Continuous-duty motor branch-circuit conductors are sized at 125 percent of the table full-load current, so 28 times 1.25 gives 35 amperes. The 32.2 figure comes from 115 percent, which belongs to an overload calculation, and 43.75 comes from taking 125 percent twice. Notice the multiplier lands on the table value rather than on anything printed on the motor.

NEC 2026 430.22, Table 430.248