The 5 Most Commonly Missed Questions on NEC Mock Exams

These are the 5 questions students miss most on JCR's free 25-question NEC mock exam. Between 63% and 72% of students got each one wrong. Each link opens the question, the answer and the 2020 NEC rule behind it.

These are JCR practice questions, not questions from a state exam. Try each one with your code book open before you look at the answer.

The 5 most-missed NEC mock exam questions

1. #1. Pull box size for an angle pull (314.28)

   72% of students got it wrong. Three raceways enter one wall of a pull box. Most people size the box from the largest raceway and forget the rest of the row.

2. #2. Continuous loads on a 100%-rated assembly (210.20(A))

   71% of students got it wrong. How much continuous load can a breaker carry when the whole assembly is listed for 100%? Old habits push most people to the wrong number.

3. #3. Breakers used as switches: SWD and HID (240.83(D))

   67% of students got it wrong. Two statements about breakers that switch fluorescent lighting. Only one is a real NEC rule.

4. #4. Motor overload sizing and service factor (430.32)

   67% of students got it wrong. A true-or-false question about a motor with a 1.10 service factor. It tests whether you read the overload percentages the right way.

5. #5. Closet light clearance (410.16(C))

   63% of students got it wrong. A fluorescent light on the wall above a closet door. The clearance most people remember belongs to a different kind of fixture.

Why students miss these NEC exam questions

Each one hides a trap: look-alike numbers, an exception, a small word or a rule that isn't there. Tried them all? Here is the takeaway for each.

• #1 Pull box: count the whole row. 314.28(A)(2) sizes an angle pull from 6 times the largest raceway, plus the sum of the other raceways in that row on the same wall. Eight times is the straight-pull rule. See the pull box math.
• #2 100%-rated assembly: read the listing. Most people answer 80 percent, the load a standard breaker carries after 125% sizing. Under the 210.20(A) exception, an assembly listed for 100% operation, overcurrent devices included, can carry its full rating. See the 100% exception.
• #3 Breakers used as switches: test each statement. 240.83(D) asks for a listing and an SWD or HID marking. "Approved for continuous duty" sounds right, but it isn't in the rule. See the SWD and HID rule.
• #4 Motor overloads: "no more than," not "at least." 430.32(A)(1) sets ceilings. A motor needs a marked service factor of 1.15 or higher, or a marked temperature rise of 40°C or less, to reach 125%. Every other motor tops out at 115%. See the overload limits.
• #5 Closet lights: match the fixture to the number. In 410.16(C), 12 in. belongs to surface-mounted incandescent or LED fixtures with an enclosed light source. Surface-mounted fluorescent gets 6 in., the same as recessed fixtures. See every closet clearance.

More practice questions

Want all 5 as a quick quiz with an answer key? Take the 2020 NEC practice test. These questions from JCR's full 500+ question mock exam also trip people up:

• Motor breaker size from Table 430.52
• Dwelling service load calculation
• Main bonding jumper size
• Ceiling box weight limits for lights and fans

See every worked example on JCR's NEC Answers page.

Common questions

Are these questions from the real electrical exam?

No. They come from JCR's practice exams, which are written on the 2020 NEC. Real exam questions are kept confidential, but they cover the same NEC topics.

What is the most-missed question on JCR's NEC mock exam?

The angle pull box question (NEC 314.28). 72% of students got it wrong, most often by leaving out the smaller raceways in the row.

Which NEC edition do these questions use?

The 2020 NEC. Several states still test on it, including North Carolina. Check which edition your state uses.

How should I practice for an open-book NEC exam?

Answer questions with your code book open and a timer running, the way you will at the test center. Look up the section for every answer, even the ones you get right.

JCR checked these questions against the 2020 NEC on October 21, 2026.