Can You Use a Code Book on the C-10 Exam?
Short answer: no. The California C-10 Electrical Contractor exam is closed book. You will not have a Code book on the desk, you cannot bring a tabbed copy, and you cannot bring notes, formula sheets, or printed tables. Same goes for the Law and Business exam.
That single fact should reshape how you study. A lot of candidates prepare as if they will be able to look things up under pressure — they get very good at flipping to a table and very bad at recalling what is in it. On a closed-book exam, the flipping skill is worth zero.
Why closed book changes the whole plan
Open-book exams reward navigation. Closed-book exams reward two things:
- Recall of values — the numbers that show up over and over.
- Procedure fluency — knowing the steps of a calculation well enough to run them without a prompt.
If you can do those two things, the exam feels reasonable. If you cannot, no amount of "I know where to find it" saves you.
The practical implication: every time you look something up while studying, ask yourself whether that value is a recurring one. If it is, it goes on your memorization list. If it is a one-off oddity, let it go — the exam is built around the common cases described in what is actually on the C-10 electrical exam, not trivia hunting.
What you can and cannot bring
Rules are set by the testing vendor CSLB contracts with, and they are enforced strictly. Treat your Notice to Appear as the governing document, and check cslb.ca.gov if anything is unclear.
| Item | Into the test room? |
|---|---|
| Valid government photo ID | Yes — required |
| Notice to Appear / scheduling confirmation | Bring it; follow the instructions on it |
| Code book (CEC/NEC), any edition | No |
| Tabs, sticky notes, highlighted printouts | No |
| Handwritten notes or formula sheets | No |
| Personal calculator | Generally no — assume not allowed |
| Phone, smart watch, earbuds, fitness tracker | No — stored in a locker |
| Bags, jackets, food, drink | No — stored outside |
| Scratch paper / erasable board | Provided by the center, not brought by you |
Anything not allowed goes in a locker before you are seated. Plan for that: leave what you do not need in the car, and do not count on having your phone during a break. More on the flow of the day in C-10 exam day: what to expect.
The calculator situation
Assume you will be using a basic calculator — either an on-screen one built into the testing software or a simple unit handed to you. Scientific and programmable calculators with memory functions are the ones test centers care most about, and they are typically barred.
What that means in practice:
- Practice without your fancy calculator. If you have been doing square-root and exponent work by pressing one button, do a few sessions with a plain four-function calculator and see how it feels. It is a different experience.
- Know your square root of 3. Three-phase math leans on 1.732 constantly. Know it, and know when it belongs in the denominator versus the numerator.
- Get comfortable with mental estimation. Being able to eyeball whether an answer is roughly right catches the keystroke errors that closed-book, timed conditions produce.
- Round the way the Code rounds. Knowing when to round up to the next standard device size versus round a demand factor is a scoring difference, not a style preference.
Voltage drop work in particular gets slower without a scientific calculator — see voltage drop calculations for the C-10 exam for the procedure to drill.
What to actually memorize
Here is where closed book stops being scary. You do not need to memorize the 2025 California Electrical Code. You need a fairly short list of high-frequency values and a handful of procedures.
Values worth knowing cold:
- Standard overcurrent device ratings in ascending order — you will be asked to select "the next standard size" repeatedly, and hesitating there costs you time on question after question.
- Common conductor ampacities for the wire sizes residential and light commercial work actually uses, at the temperature columns that matter, plus how termination temperature ratings limit what you can use.
- Ambient temperature and conductor-count adjustment concepts — including where they apply and how they stack.
- Box fill volume allowances per conductor size, and what counts as a conductor (devices, clamps, grounds, and how they are tallied).
- Conduit fill percentages for one, two, and over-two conductors.
- Grounding and bonding conductor sizing logic — the difference between an equipment grounding conductor and a grounding electrode conductor, and what each is sized from.
- General lighting load values per square foot for common occupancies, and the demand factors that apply to them.
- Motor sizing multipliers — the percentages used for branch-circuit conductors, overload protection, and short-circuit/ground-fault protection.
- GFCI and AFCI required locations — these are pure recall questions and free points if you have them memorized.
Procedures worth being fluent in:
- Dwelling unit service and feeder load calculations, standard method, start to finish.
- Conductor sizing from load to ampacity to overcurrent device, including the adjustment and correction steps in the right order.
- Voltage drop, single-phase and three-phase.
- Motor and transformer calculations, including full-load current lookups and the protection percentages.
- Box fill and conduit fill from a described installation.
Each of those has a dedicated deep dive: load calculations, conductor ampacity and sizing, grounding and bonding, and conduit and box fill.
How to study for a closed-book exam
The method that works is boring and effective:
Study with the Code book open, test yourself with it closed. Read the section, understand why the rule exists, then close the book and reproduce the value from memory. Understanding beats rote memorization because it survives a reworded question — but you still need the number.
Build your own one-page value sheet by hand. Not to bring anywhere — writing it repeatedly is the point. Rewrite it from memory once a week and see what falls out. The gaps are your study list.
Drill calculations to the point of boredom. A load calculation you have done forty times takes three minutes under pressure. One you have done four times takes twelve, and you do not have twelve.
Do questions under time. This is the part people skip. Untimed practice with the book nearby measures nothing about how you will perform in a proctored room with a countdown clock. See how to study for the C-10 exam for a full schedule, and C-10 exam format and passing score for how the sections are weighted so you can spend your hours where the questions are.
The bottom line
Closed book is not a trick — it is a signal about what the exam is measuring. It wants a contractor who has the common numbers in their head and can run the standard calculations without stopping to research. That is a real-world skill, and it is trainable in a few weeks of honest work.
The fastest way to find out which values you actually have and which ones you only think you have is to sit down with a timer and work through questions cold, no book, no notes. That is the closest thing to the real thing, and it tends to be a very informative afternoon.