What's Actually on the C-10 Electrical Exam

The C-10 isn't one test. To get licensed as an electrical contractor in California you sit for two exams: the Trade exam (the electrical knowledge) and the Law and Business exam (running a contracting business legally). You pass both or you pass neither. Plenty of sharp field electricians clear the trade side and then get blindsided by the business side, so treat them as two separate projects.

Here's what each one covers, how the questions are distributed, and the spots where candidates bleed points.

The Trade exam is built from a blueprint

The CSLB doesn't write trade questions at random. Every classification has an exam content outline — a blueprint — that groups the material into major areas and assigns each a percentage weight. That weight tells you roughly how many questions come from each area. It's the single most useful study document you'll find, because it tells you where the points live.

Section names and percentages get updated periodically, so pull the current C-10 exam content outline straight from the CSLB before you start studying. The shape has been stable for years, and it looks like this:

Those are the percentages in CSLB's own C-10 study guide, which calls them approximate. Planning and Estimating plus Rough Wiring is more than half the exam, and Planning and Estimating is where most of the calculation questions live.

The calculation questions are the whole ballgame

The questions that involve a code lookup or a math step are what decide most exams. They take longer, they're easier to get wrong, and there are a lot of them. Get comfortable with these before anything else:

• Dwelling load calculations. Standard method vs. the optional method (NEC 220.82), general lighting loads, small-appliance and laundry circuits, ranges, dryers, HVAC. This is the number-one place people lose time and points — work through dwelling load calculations until they're automatic.
• Conductor ampacity and sizing. Table 310.16, temperature correction, ambient adjustment, and the termination-temperature rule in 110.14(C) that quietly caps a lot of answers. Our walkthrough on conductor ampacity and wire sizing covers the traps.
• Overcurrent protection. Breaker and fuse sizing, the "next size up" rule in 240.4(B), tap rules. See overcurrent protection on the C-10 exam.
• Conduit fill and box fill. Chapter 9 tables plus 314.16 for boxes. Pure lookup once you know the procedure.
• Motors and transformers. Motor tables (430.250), with separate rules for conductor sizing, overload, and short-circuit protection. Different rules for the same motor — that's the whole test.
• Voltage drop. Not a hard code mandate for branch circuits, but it shows up as a calculation. Know the formula cold.

Get those six categories fast and accurate under time pressure and the trade exam stops being scary.

Where candidates actually lose points

After watching a lot of people take this test, the failures cluster in the same few places.

Grounding vs. bonding. People use the words interchangeably in the field and then can't tell a grounding electrode conductor from an equipment bonding jumper on the exam. Article 250 is dense and the exam leans on it hard. If you deep-clean one conceptual topic, make it grounding vs. bonding.

Reading the wrong table. Ampacity questions punish you for grabbing the number off Table 310.16 without applying correction and adjustment factors, or for ignoring the 60°C/75°C termination limit. The answer choices are built so the un-adjusted number is one of the options — it's a trap, not a typo.

GFCI/AFCI locations. 210.8 and 210.12 change with almost every code cycle. Candidates study an old edition and miss current required locations — dishwashers, outdoor receptacles, basements. Study the current GFCI and AFCI requirements, not what you remember from your apprenticeship.

Running out of time. Every one of these is a slow question, and the clock is real. Speed comes from having the procedures and the common values in recall, not from being smarter than the next candidate.

Know the code cold, because you won't have it

The trade exam is closed book, so nothing you need can be looked up at the testing center. California adopts the 2023 NEC as the 2025 California Electrical Code, with state amendments — so study the California edition, not a plain NEC. Study with it open, then close it and reproduce the values: the Table 310.16 ampacities you use most, the Article 220 demand factors, the Chapter 9 fill percentages. The exam rewards recall and a clean method, not page-flipping.

The Law and Business exam is its own animal

This is where strong electricians get humbled. The Law and Business exam is the same test every contractor classification takes, and none of it is electrical. It covers:

• Business organization and licensing law (who can hold a license, bonds, workers' comp)
• Contracts, including the home-improvement contract rules the CSLB enforces aggressively
• Employment and payroll — prevailing wage, workers' comp, payroll taxes, safety
• Mechanics liens, preliminary notices, and getting paid
• Public works, insurance, and basic financial management

None of that is intuitive if you've spent your career pulling wire. Budget real study time and work through the Law and Business exam study guide as a distinct subject. The candidates who wing it here are the ones retaking a test they thought was the easy one.

How to actually prepare

Two exams, two study plans. For the trade side, drill the six calculation categories and the grounding/bonding concepts until they're reflexes. For the business side, treat it like learning a new subject, because it is. The people who pass on the first try aren't the ones who read the most — they're the ones who worked the most practice questions and full-length timed runs, so the format and the clock feel routine on exam day. Working problems under time is how the material sticks.

Everything above is meant to help you study smarter — always confirm current sections, weights, and fees with the CSLB and defer to the official code and current exam outline. For a clearer picture of test day itself, read up on the C-10 exam format and passing score next.