Which NEC topics does this cover?

Four core load-calculation areas tested on licensing exams: single-phase voltage drop, outlet box fill under 314.16, conduit fill using the Chapter 9 forty-percent limit, and the standard-method dwelling service load under Article 220. Each problem is generated with fresh random numbers so you can drill the method repeatedly.

How is voltage drop calculated here?

It uses the single-phase formula VD equals 2 times K times I times L divided by circular mils, with K of 12.9 for copper. The conductor's circular mils come from the standard AWG table. The result is then expressed as a percent of nominal voltage, which the NEC recommends keeping at or below three percent on a branch circuit.

What counts toward box fill?

Per 314.16(B) each conductor passing through counts once by its AWG volume allowance, all equipment grounds together count as one, all internal cable clamps together count as one, and each device yoke counts as two of the largest conductor. The tool sums these counts and multiplies by the per-conductor cubic-inch allowance.

How does the dwelling service demand work?

The standard method adds general lighting at 3 VA per square foot, two 1500 VA small-appliance circuits, a 1500 VA laundry circuit, and any fixed appliances, then applies the demand factor: the first 3000 VA at 100 percent and the remainder at 35 percent. Dividing by 240 volts gives the calculated service current.

Is this a substitute for the code book?

No. It drills the methods using standard values and tolerances, but real installations depend on the exact code edition your jurisdiction has adopted, correction and adjustment factors, and table footnotes. Always verify your work against the current NEC and any local amendments.

Electrical Apprentice NEC Code Study Calculator

Passing a journeyman or master electrician exam comes down to executing a handful of load-calculation methods quickly and correctly under time pressure. This study tool generates an endless supply of fresh problems in the four areas that show up most — voltage drop, box fill, conduit fill, and the dwelling service load — grades your answer, and walks through the full solution so you learn the method, not just the number.

How it works

Each problem is generated with random but realistic inputs and a deterministic, code-correct answer. The formulas follow standard NEC methods:

Voltage drop (1-phase):  VD = 2 x K x I x L / CM      (K = 12.9 copper)
Box fill (314.16):       volume = sum_of_counts x per-AWG allowance
Conduit fill (Ch.9):     required area = conductor area / 0.40
Dwelling service (220):  demand = 3000 + (connected - 3000) x 0.35

Your typed answer is compared against the exact result within a small tolerance, so rounding the way you would on the exam still grades as correct. The running score tracks how many you have gotten right.

Tips and example

A typical voltage-drop problem might give a 30 A load on a 150 ft run of 10 AWG copper at 240 V. Plugging in: VD equals 2 times 12.9 times 30 times 150 divided by 10,380 circular mils, which is about 1.12 V, or roughly 0.47 percent — well under the three-percent guideline.

Work each problem on paper exactly as you would in the exam room before checking, and always reveal the solution on the ones you miss so you internalize the code reference, not just the arithmetic. Switch the category selector to drill a single weak area until it is automatic, then return to random to keep all four sharp.