Short answer: After every practice test, write down each miss and give it one cause: wrong article, wrong table column, skipped step, rounding, misread question or out of time. Count the causes and fix the biggest one first, because one cause usually costs more points than any single topic. A miss you only mark wrong and never sort will come back on the real exam.
A mistake log needs a steady supply of scored misses. The Practice Pack gives you 10 full timed two-part mocks with a score by part and by topic, a wrong-answer list and a weak-area check, and unlimited retakes. Its 299 step-by-step calculation solutions show the exact step where your work split from the right answer, so you can name the cause. US$39, one payment.
Tsai Electro is an independent learning site. Not affiliated with TDLR, PSI or NFPA. Exam rules can change, so confirm in the PSI bulletin linked below.
The six causes and how to spot them
| Cause | What it looks like | First fix |
|---|---|---|
| Wrong article | You answered from a rule that does not cover the question | Drill the lookup path, for example Article 210 to 210.19 |
| Wrong table column | Right table, wrong temperature column or wrong row | Say the column out loud before you read the value |
| Skipped step | You left out a percentage, a factor or a second condition | Write the steps as a list before you calculate |
| Rounding | Rounded too early, or rounded the wrong way | Round only at the step the method says |
| Misread question | Missed “copper unless noted”, a named method or the unit asked for | Reread the last line of the question before you answer |
| Out of time | Guessed because the clock ran down | Practice skip-and-return on a timed mock |
Our workbook lists traps that fit straight into these causes:
- Wrong table column: derating from the 75 C column instead of the 90 C column in Table 310.16.
- Skipped step: forgetting 125% on lighting, show window and sign loads that run all day.
- Wrong article or method: sizing motor conductors from nameplate current when 430.6(A)(1) sends you to the table full-load current.
- Misread question: taking the 75% demand with only three fastened-in-place appliances; 120.53 needs four or more.
How to keep the log
- Take the test on the clock. Untimed practice hides your “out of time” cause.
- Mark guesses as you go on your practice sheet, so a lucky guess still counts as a weak spot.
- Check every miss against the code path. Find the article, section or table that answers it, then pick the one cause that fits best.
- Count the causes with the calculator below.
- Fix the top cause first, then retest. A cause that stays the same needs a different drill.
Keep one line per miss: test name, question number, part, cause, and the correct code path. That last column turns the log into a lookup drill.
Read the log by part
Keep a separate count for each part, and sort the weaker part first. On NEC Knowledge the work is finding the rule fast, so watch wrong article and out of time. On Calculations the work is the setup and the math, so watch skipped step, rounding and wrong table column.
The bulletin says not to consider code exceptions or optional calculation methods unless the question directs you to. A miss from using one anyway goes under misread question.
Sort your misses
Mistake log by cause
Enter how many misses you had in each cause on one practice test or a set of tests. The counts shown are an example to replace with your own log.
- Wrong article
- Wrong table column
- Skipped step
- Rounding
- Misread question
- Out of time
[ETOS_ACCOUNT_CARD]
How do I review a failed journeyman practice test?
Find the code path that answers each miss and give it one cause. Then count the causes and drill the biggest one before your next timed mock.
What are common mistakes on the journeyman calculations part?
Our workbook flags traps such as derating from the 75 C column instead of 90 C, forgetting 125% on continuous loads, sizing motor conductors from nameplate current and using the full raceway area instead of the 40% area. Each one fits a cause in the log.
Does the real exam tell me what I got wrong?
A failing candidate gets a diagnostic report of strengths and weaknesses right after the exam. It shows weak areas, so a mistake log from your own practice is still the way to find the cause behind them.
Sources checked October 2026
As an Amazon Associate, I earn from qualifying purchases.
