The C-10 Electrical Contractor License is one of the most in-demand CSLB classifications in California. If you want to legally install, alter, or repair electrical systems — from residential wiring to commercial power distribution — you need to pass the C-10 trade exam. This guide covers exam topics, study tips, and strategies specific to the C-10 classification so you can pass with confidence in 2026.
What Does a C-10 License Allow You to Do?
A C-10 Electrical contractor is authorized to install, service, and maintain electrical systems including:
- Power distribution and branch circuit wiring
- Lighting systems (residential, commercial, industrial)
- Low-voltage systems (fire alarms, communications, security)
- Solar photovoltaic electrical connections
- Motor controls and industrial electrical equipment
- Emergency and standby power systems
The C-10 is separate from the C-46 (Solar) and C-7 (Low Voltage) classifications, though there is some overlap. If your primary work involves general electrical installation and repair, the C-10 is the classification you need.
C-10 Exam Format
The C-10 trade exam is a computer-based, multiple-choice test administered at PSI testing centers. Key details:
- Number of questions: approximately 100–110
- Time limit: 3.5 hours
- Passing score: 72%
- Open-book: Yes — you will have digital access to the National Electrical Code (NEC) during the exam
Remember, you must also pass the Law & Business exam separately. Both require a 72% to pass.
Key Exam Topics
The C-10 trade exam draws heavily from the National Electrical Code (NEC) and California-specific amendments. Here are the major topic areas:
1. General Electrical Knowledge (25–30%)
Ohm’s law, voltage drop calculations, power formulas, conductor sizing, and basic circuit theory. These fundamentals appear throughout the exam.
2. NEC Code Application (30–35%)
Expect questions requiring you to look up specific NEC articles. Common areas include:
- Article 210 — Branch circuits
- Article 220 — Load calculations
- Article 250 — Grounding and bonding
- Article 300 — Wiring methods
- Article 310 — Conductor ampacity tables
- Article 430 — Motors and motor circuits
3. Safety and OSHA Requirements (10–15%)
Lockout/tagout procedures, personal protective equipment, arc flash safety, working clearances (NEC 110.26), and Cal/OSHA electrical safety orders.
4. Installation Practices (15–20%)
Raceway and conduit installation, box fill calculations (Article 314), cable tray systems, grounding electrode systems, and proper termination methods.
5. Plan Reading and Estimating (5–10%)
Reading electrical blueprints, interpreting symbols, understanding single-line diagrams, and basic project estimation.
Study Tips Specific to the C-10 Exam
Master NEC Navigation
The exam is open-book, but the NEC is over 800 pages. If you can’t find answers quickly, the time limit will beat you. Practice using the index and table of contents until you can locate any article in under 60 seconds. Focus on the articles listed above — they account for the majority of code-lookup questions.
Memorize Key Formulas
While the NEC is available, doing basic calculations from memory saves enormous time:
- Ohm’s Law: V = I × R
- Power: P = V × I
- Voltage drop: Vd = (2 × K × I × D) / CM
- VA per square foot for dwelling load calculations (NEC 220.12)
Practice with Realistic Questions
Generic electrical study guides won’t prepare you for CSLB-specific question phrasing. Our C-10 exam prep course features hundreds of practice questions modeled on actual exam content, complete with detailed explanations for every answer.
Don’t Neglect Grounding
Article 250 (Grounding and Bonding) is one of the most heavily tested sections. Many test-takers underestimate its complexity. Study grounding electrode systems, equipment grounding conductors, and bonding requirements thoroughly.
C-10 Pass Rates and What They Tell You
The C-10 exam has historically had a moderate pass rate — roughly in the 45–55% range for first-time takers. This is not meant to discourage you; it means that preparation matters. Candidates who use structured study programs pass at significantly higher rates than those who walk in relying solely on field experience.
Timeline: From Application to License
- Submit application with 4 years of electrical experience ( fee)
- Wait for approval (6–10 weeks)
- Schedule and pass both the C-10 trade exam and Law & Business exam
- Post your bond (,000) and workers’ comp insurance
- Receive your active license
Start Your C-10 Exam Prep Today
The C-10 Electrical exam is passable with the right preparation. Focus on NEC navigation, core formulas, and grounding — then reinforce everything with practice tests. Explore our C-10 exam prep course to access practice exams, topic reviews, and study schedules built specifically for this classification. Don’t leave your license to chance — check our pricing and start studying today.