The Electrical (C-10) Exam: Format, Topics, and Passing Score
The C-10 exam is a closed-book, four-choice, computer-assisted trade examination at PSI, with 3.5 hours to complete it. CSLB does not publish one universal question count or numeric passing score on the public trade guide; the percentage required to pass is provided at the test site. The practical answer to the C-10 exam topics and passing score question is therefore to use the official blueprint and your test-site instructions.
The exam at a glance
| Exam item | Current answer |
|---|---|
| Format | Closed book; multiple choice with four choices |
| Location | PSI computer-assisted testing site |
| Time | 3.5 hours for each exam |
| Public question count | No universal public question count |
| Passing score | CSLB says the required percentage is provided at the test site |
| Retake and eligibility | 21 calendar days after a failed exam; 18-month eligibility period |
| Trade blueprint | Official study guide |
What the C-10 exam covers
The official C10 study guide is the controlling source for the blueprint. Its percentages are approximate, but they show where the exam writers expect the greatest concentration of knowledge.
1. Planning and Estimating (28%)
Existing system evaluation; plans and specifications; electrical calculations; code requirements; material selection; energy production and storage project planning.
2. Rough Wiring (27%)
System layout; clearances; raceways and panels; wire and equipment installation; grounding and bonding; rough energy-storage wiring.
3. Finish Wiring and Trim (11%)
Finish device placement; motors and equipment; labels; trims and sealants; finish wiring for energy systems.
4. Startup, Troubleshooting, and Maintenance (16%)
Energizing and testing; common electrical problems; locating and repairing failed components; test equipment; energy-system performance.
5. Safety (18%)
Lockout/tagout; PPE; tools and equipment; hazardous materials; job-site environments.
How to use the topic weights
The percentages are approximate, but they are still useful. A section with 38% deserves more study time than one with 20%, and a section with 11% should not consume the same number of evenings. The C10 guide also says the exam is written around one best answer, some questions require computation, a calculator is provided, and there is no penalty for guessing. Those details favor a repeatable process: identify the task, eliminate answers that violate the rule or unit, then choose the best remaining answer.
The official CSLB C-10 classification page is useful when you need to confirm scope, while the California contractor license roadmap connects the exam to experience and application steps.
A study plan that follows the blueprint
- Read the free Official study guide and make a one-page map of the weighted sections.
- Work through the Peerless Electrical (C-10) Study Guide Book in the same order as the blueprint.
- Pair the trade work with the CSLB Law & Business practice exam; every California contractor applicant must pass the business-and-law exam as well as any required trade exam.
- Use the Peerless Electrical online practice exam in timed blocks. Review every miss, including a lucky guess, and write the rule or calculation that should have controlled the answer.
- Before scheduling, aim for consistent 85%+ practice results across more than one session. That is a study checkpoint, not a CSLB passing-score claim.
One worked example
A 120-volt load draws 10 amps. What is its power?
- A. 12 watts
- B. 120 watts
- C. 1,200 watts
- D. 12,000 watts
Correct answer: C
Use P = V × I. Multiplying 120 volts by 10 amps gives 1,200 watts. The point is to recognize the relationship and choose the best answer, not to memorize a question.
How to practice without guessing
A practice score is useful only when it changes what you study next. Keep a small error log with three columns: topic, reason for the miss, and the rule or calculation that fixes it. If the same topic appears twice, return to the book before doing another random quiz. If you miss because you rushed, repeat the question slowly and identify the words that set the scope, unit, or safety condition.
Do not confuse a practice target with the official result. CSLB keeps its exam questions confidential and tells applicants the percentage needed to pass at the testing site. The most reliable preparation is therefore blueprint-based review, fresh questions, and honest correction of weak sections.
FAQ
How many questions are on the C-10 exam?
CSLB’s public trade study guides do not give one universal question count. Read every item and use the current Notice to Schedule and PSI instructions for the appointment-specific information.
What passing score do I need on the C-10 exam?
CSLB says applicants are told the percentage of correct answers needed to pass at the test site. Do not rely on an unverified percentage from a study forum or older article.
Is the C-10 exam open book?
No. The official C10 study guide describes the trade exam as closed book. Prepare by recalling the rule, calculation, or sequence without having the reference open beside you.
Can I use a calculator?
The CSLB study guides say some questions require mathematical computation and that a calculator will be provided. Practice setting up the calculation first, then check the arithmetic.
Are practice questions actual CSLB questions?
No. CSLB says test questions and answer keys are not available for review. Practice questions should be fresh exercises based on the published topic blueprint, not copied exam content.
Sources
- CSLB: Studying for the examination
- CSLB: My original exam application was accepted
- CSLB: Before applying for a license
- CSLB: C10 examination study guide
- CSLB: C-10 classification
Peerless Institute has helped Californians prepare for CSLB exams since 1953. Use the Peerless Electrical Study Guide Book with the online practice exam; the Silver bundle puts both trade-prep pieces together. The trade exam is only one part of the application, so review the Law & Business exam guide and practice exam before test day.