Maryland voltage drop practice
Voltage drop is one of those topics that looks simple and still costs guys points on test day. The Maryland exam is open book on the 2020 NEC, so the trap is not memorizing a number. It is knowing the 3 percent figure is a recommendation, not a rule, and running the formula clean under the clock.
Last reviewed June 2026
Why voltage drop is on the test at all
The NEC does not enforce a hard voltage-drop limit on a standard branch circuit. The 3 percent figure most people quote lives in an informational note under NEC 210.19. Informational notes are recommendations, not enforceable rules, and that is exactly the distinction the exam likes to test. A question can show you a run that exceeds 3 percent and ask whether it is acceptable. The honest answer is that it is past the recommendation, so you would size the conductor up.
Because the Maryland exam is open book, you are not asked to memorize this. You are asked to know which article to open and run the math fast enough to finish.
The formula, set up the same way every time
For a single-phase circuit, voltage drop is two times K times the current times the one-way length, divided by the conductor circular mils. K is about 12.9 for copper. You double the length because the current runs out and back. The two places people slip are forgetting the factor of two and mixing up circular mils with conductor size, so lock the setup in before exam day.
- VD is the voltage drop in volts.
- K is about 12.9 for copper.
- I is the load current in amps.
- L is the one-way length in feet (the formula doubles it for the round trip).
- Circular mils is the conductor area from NEC Chapter 9, Table 8.
Worked example
Take a 120 volt single-phase circuit carrying 16 amps a distance of 100 feet on 12 AWG copper. From NEC Chapter 9, Table 8, 12 AWG copper is 6,530 circular mils. Run it through the formula.
That 5.3 percent is well past the 3 percent the NEC recommends in the 210.19 informational note. So this run does not meet the recommendation, and the fix is to upsize the wire. A larger conductor has more circular mils, and circular mils is the denominator, so a bigger wire pulls the voltage drop back down. If a question asks whether this run is acceptable, the answer is no, and the next move is the next conductor size up.
Why this topic quietly costs points
Voltage drop punishes two habits. Guys who studied closed-book style try to recall the rule and get the recommendation-versus-requirement distinction backwards. Guys who rush the math drop the factor of two or grab the wrong circular-mils value and land on a clean-looking wrong number. Both lose a question they could have banked.
On a 70-question journeyperson exam where 70% clears it, that is 49 correct out of 70. Every calculation you can set up in 30 seconds buys back time for the lookups that take longer. Voltage drop is one of the cheapest points to earn once the setup is automatic.
How to practice it the right way
Do not grind a giant trivia bank. Find out whether voltage drop and the 210.19 note are actually costing you points first, then drill that flip path until the formula and the conductor table are second nature. Run the free diagnostic, see where you stand, and put your nights on the article families that are dragging the score.
Ready to see where you stand? Take the free Maryland diagnostic.
Where these exam facts come from: Maryland State Board of Electricians — License Requirements, PSI Maryland Master & Journeyperson Candidate Bulletin, Maryland Electricians Act (SB 762, 2021), COMAR 09.09.02.01 (continuing education). Last reviewed June 2026.
See if voltage drop is costing you points
The free diagnostic shows which article families are dragging your Maryland score, so you drill voltage drop and the rest of your weak spots instead of everything. Then the full platform runs original questions on the 2020 NEC that walk the formula and the codebook flip path.