Michigan voltage drop practice questions

The pattern these questions follow

Voltage drop questions on the 2023 NEC exam are predictable once you have seen a few. You are handed a voltage, a current, a one-way distance, and a conductor size. Your job is to run the drop in volts, turn it into a percentage of the source voltage, and decide whether it clears the limit the NEC recommends. The same shape repeats with different numbers, so the win is recognizing it fast and setting it up without thinking.

• Single phase: 2 times K times I times L, divided by circular mils.
• Three phase: swap the 2 for 1.732, everything else holds.
• K is about 12.9 for copper and about 21.2 for aluminum.
• L is the one-way distance in feet. The 2 in the formula already accounts for the run out and back.
• Use the load current the question gives you, not the breaker or overcurrent device rating.

Worked example

Take a 120 volt single-phase circuit carrying 16 amps a one-way distance of 100 feet on 12 AWG copper, which is 6,530 circular mils. Run the drop, then read it against the recommendation.

1. Write the formula. VD = (2 × K × I × L) ÷ circular mils, with K about 12.9 for copper.
2. Plug in the numbers. VD = (2 × 12.9 × 16 × 100) ÷ 6,530.
3. Solve. The top is 412,800. Divide by 6,530 and you get 6.3 volts of drop.
4. Turn it into a percentage. 6.3 volts is 5.3% of 120 volts.
5. Judge it. 5.3% is past the 3% the NEC recommends in the 210.19 informational note, so you would upsize the wire to bring the drop back down.

Notice what the exam is really checking. It is not asking you to memorize a table. It is checking whether you can set up the formula, keep the units straight, and know that 3% is the line for a branch circuit. Get those three things automatic and this question stops eating your clock.

Why this topic costs points

Voltage drop bleeds points for reasons that have nothing to do with being a bad electrician. The math is short, but the traps are quiet, and on an open-book exam guys try to find the answer in the code instead of running it. There is no table to flip to here. You either know the formula or you lose the question and the time you spent hunting for it.

• Using the breaker rating instead of the actual load current.
• Forgetting the 2 for single phase or the 1.732 for three phase, which throws the answer by a wide margin.
• Doubling the distance by hand when the formula’s 2 already covers the round trip.
• Reading the drop in volts but never converting it to a percentage, so you cannot tell if it clears the 3% line.
• Treating the 210.19 informational note as a hard pass-fail rule. It is a recommendation, but the exam still expects you to know the 3% and 5% figures.

How to drill it for the Michigan exam

Reading one worked example is not the same as being fast under a timer. The Michigan exam gives you under two minutes a question, and calculations like this eat more than their share. So the prep that moves your score is repetition on the same pattern with fresh numbers until the setup is reflex, not understanding it once and moving on.

Start with the free diagnostic

Before you grind random questions, find out whether voltage drop is even one of your weak spots. The free 15-minute diagnostic projects your score and points to the NEC chapters costing you the most. If calculations are your gap, you will see it, and you can spend your nights there instead of guessing.

From there, the JourneymanIQ Michigan bank drills voltage drop and the rest of the calculation chapters with original questions that cite the NEC article behind each answer. We are not going to quote a count of voltage drop questions in the bank, because we have not verified per-topic numbers and we do not invent them. What we will tell you is the format the bank trains: the same 80-question, 150-minute, 75%-to-pass shape the PSI exam uses, on the 2023 NEC.

Voltage drop FAQ