The C-10 Electrical Exam Study Guide: Everything to Cover

The C-10 exam isn't a mystery. The CSLB publishes a blueprint that tells you which subject areas the trade exam pulls from and roughly how much weight each one carries. Study to that blueprint instead of guessing, and you stop burning hours on topics worth two questions while ignoring the areas worth twenty. This guide walks the whole thing section by section, points you to the deeper topic guides, and lays out a sane order to work through it.

One note before we start: everything below explains concepts to help you study. The technical content is grounded in the 2023 NEC as adopted by the 2025 California Electrical Code, but the exam draws from the current adopted edition and the CSLB can adjust its content outlines. Always defer to the official code and confirm current details at cslb.ca.gov.

Two exams, not one

Getting the license means passing two separate tests: the trade exam (electrical knowledge) and the Law and Business exam (contracts, employment, safety, business practices). They're scored independently. Plenty of strong field electricians clear the trade side and stumble on Law and Business because they never opened a book on lien rights or workers' comp. Treat them as two study projects. This article covers the trade exam in depth; the Law and Business exam has its own study guide worth reading early.

For the ground rules on format, question count, and what a passing score means, start with the C-10 exam format and passing score breakdown.

The trade exam blueprint, weighted

The trade exam splits into major subject areas, each carrying a share of the questions. The CSLB groups them roughly like this — confirm the current percentages on your exam bulletin, but the relative emphasis has held steady for years:

The two heavyweight sections, Planning and Estimating and Rough Wiring, are more than half the exam. That's also where the math sits. If your calculations are shaky, no amount of memorizing definitions saves you.

Calculations: where the exam is won or lost

More candidates lose points to arithmetic than to any single code concept. The good news: the calculation types repeat, and once you've drilled them they turn into free points. Cover all five.

• Dwelling load calculations. The standard method (Article 220, Part III) and the optional method for a single dwelling (220.82). Know when general lighting loads, small-appliance circuits, and the largest-motor rule apply. Work the full sequence in the dwelling load calculation guide.
• Conductor ampacity and sizing. Table 310.16, the temperature-correction and conductor-adjustment factors, and the 60/75/90°C termination rules. This is the backbone of half the wiring questions — the conductor ampacity and wire sizing guide breaks it down.
• Conduit and box fill. Chapter 9 tables for raceway fill, 314.16 for box fill. Tedious, but mechanical once you learn the steps. See conduit fill and box fill calculations.
• Voltage drop. Not a hard NEC mandate for general branch circuits, but tested as a design concept and flagged in informational notes (see 210.19 and 215.2). Know the single-phase and three-phase formulas cold — voltage drop calculations has the worked examples.
• Motor and transformer calculations. Motor FLC from Tables 430.248/430.250, conductor sizing at 125%, and overcurrent device sizing — a different animal from ordinary branch-circuit math. The motor and transformer calculation guide walks it.

Do these with a pencil and the book closed, exactly like exam day. Speed comes from reps, not from reading.

Grounding, bonding, and protection — the concept killers

Article 250 is dense, and the exam knows it. The distinction that trips up the most people is grounding versus bonding — two different jobs that share a lot of hardware. If you can't cleanly explain why a grounding electrode conductor isn't the same thing as an equipment bonding jumper, spend time on grounding vs. bonding, the topic that trips people up before test day.

Overcurrent protection is its own cluster: breaker and fuse ratings, overload versus short-circuit protection, tap rules, and the standard ratings from 240.6. Pair that with how overcurrent protection is tested on the C-10.

Then there's GFCI and AFCI — location-and-application memory work. The exam loves asking whether a specific receptacle requires GFCI protection (210.8) or whether a circuit needs AFCI (210.12). These are gift questions if you've memorized the lists and brutal ones if you haven't. The GFCI and AFCI requirements guide has the current lists.

A study order that actually works

Don't grind the blueprint top to bottom. Build from the fundamentals the calculations depend on.

1. Weeks 1–2: Conductor ampacity and Ohm's law fundamentals. Everything downstream needs these.
2. Weeks 2–4: Load calculations and conduit/box fill. The heaviest-weighted math.
3. Weeks 4–5: Grounding/bonding and overcurrent protection. Concept-heavy and code-lookup intensive.
4. Weeks 5–6: Motors, transformers, GFCI/AFCI, voltage drop. The specialized topics.
5. Weeks 6–7: Law and Business. Run it in parallel if you have the bandwidth.
6. Final weeks: full timed practice exams. Nothing else replicates the pressure.

That's a frame, not a law — compress or stretch it to your schedule. For a realistic timeline on the whole licensing process, see how long it takes to get a C-10 license, and for the study method itself, how to study for the C-10 exam without wasting months.

Use the code book to study, not to test

Both exams are closed book. CSLB's own study guide says no reference materials may be used, and a calculator is provided. So the book is for study: read a section, close it, and reproduce the value or the steps from memory. Do that with Table 310.16, the Article 250 sizing tables and the Chapter 9 fill rules until the numbers come without looking. The candidates who finish with time to spare are the ones who never have to rebuild a value from scratch.

Bottom line

The C-10 trade exam rewards two things: solid calculation reps and having the code's key values in recall. Study to the blueprint weights, drill the five calculation types until they're boring, and lock down the grounding/bonding and GFCI/AFCI details that separate a pass from a retake. The only way to know you're ready is to sit timed practice exams under real conditions. Do enough of those and exam day feels like just another Tuesday. Wondering how tough it really is? Here's an honest look at how hard the C-10 exam is.