C-10 Electrical Practice Test — California (CSLB)

What's on the C-10 Electrical exam

The C-10 is CSLB's trade exam for electrical contractors. It assumes you can pull wire and checks whether you plan, install and commission to California code. The official study guide splits it into five weighted sections, and the weights are lopsided — planning and rough wiring together are more than half the exam.

Planning and estimating (28%)

The largest section: evaluating an existing system, reading plans and specifications, electrical calculations, code requirements, material selection, and planning energy production and storage projects — photovoltaic, wind, generators, batteries, capacitors. Dwelling load calculations follow the Code, not the job: general lighting is figured at 3 volt-amperes per square foot of the building's outside dimensions, excluding open porches, garages and unfinished space not adaptable for future use, and the two required small-appliance circuits and the laundry circuit count 1,500 volt-amperes each, plugged in or not. The familiar 3% branch-circuit and 5% total voltage-drop figures sit in the Code's informational notes: guidance, not an enforceable limit.

Rough wiring (27%)

System layout, clearance and accessibility, raceway and panel installation, grounding and bonding, and rough wiring for energy production and storage. Minimum cover underground depends on the wiring method: 24 inches for direct-buried cable, 18 inches for nonmetallic raceway, only 6 inches for rigid or intermediate metal conduit, and 12 inches for a residential branch circuit rated 120 volts and 20 amperes or less with GFCI (ground-fault circuit interrupter) protection. A bored hole sits at least 1-1/4 inches back from the edge of the stud, or the cable gets a steel plate. And 25 ohms is not a resistance the grounding system must achieve — it is the measurement that excuses a single rod from needing a second.

Finish wiring and trim (11%)

The smallest section: finish device placement, motor and equipment installation, wire and equipment labeling, trims and sealants. Both traps are about reading the right number off the right place. On a motor, the branch-circuit conductors and the short-circuit and ground-fault protection are sized from the Code's full-load current tables, while the running overload protection is sized from the motor nameplate's full-load amperes — swapping the two is the classic miss. Labeling is a code requirement, not housekeeping: a panelboard directory must state each circuit's clear, evident and specific purpose, and identification that depends on who lives there today does not qualify.

Startup, troubleshooting, and maintenance (16%)

Energizing and testing, common electrical problems, locating and replacing inoperable components, choosing test equipment, and energy system performance. Learn symptom-to-cause chains, not parts lists. Lights that brighten in half the house and dim in the other half as loads switch is the signature of a lost neutral: the two 120-volt halves end up in series across 240 volts, so the lightly loaded leg climbs while the loaded leg collapses. And a module's open-circuit voltage rises as it gets colder, which is why maximum system voltage is calculated for the lowest expected ambient temperature, not the 25 °C nameplate — a string that measures fine in August can push an inverter past its limit in January.

Safety (18%)

Lockout/tagout, personal protective equipment, tools, hazardous materials and jobsite environments — in California, Cal/OSHA's Electrical Safety Orders in Title 8 of the California Code of Regulations. Approved insulated gloves are required above 250 volts to ground, and acetate, nylon, polyester or rayon clothing is barred for anyone exposed to flames or electric arcs unless the fabric is flame-retardant treated (§2320.2). Connecting de-energized equipment to a live circuit, you attach the wire to the de-energized part first; disconnecting, you remove the source end first. Overhead clearances come in two flavours: 6 feet from a 600-to-50,000-volt line, but 10 feet for material storage and boom-type lifting equipment (§2946).

How exam day works

You take the C-10 on a computer at a PSI test center, closed book, with 3-1/2 hours for the exam — the limit published in CSLB's official Examinations FAQ. Questions are multiple choice with four choices and one best answer; some need arithmetic, and while you cannot bring a calculator, the study guide says one is provided. There is no penalty for guessing, so never leave a blank. You get a printed pass/fail report before you leave; a failing one breaks the result down by section. You may retake after 21 calendar days, paying PSI a re-examination fee, inside your application's 18-month window. The C-10 is not among the ten exams CSLB publishes in Spanish; for other trades and languages CSLB may allow a translator you choose, approved by the Board in advance — that review takes four to six weeks. Every C-10 applicant also sits the CSLB Law & Business exam.

A realistic study plan

The LICENA C-10 course is 500 questions across 5 blocks. At 30 a day that is about three weeks: two full passes, with room to re-drill your weakest block. Weight your effort the way the exam does: planning (28%) and rough wiring (27%) dominate, while finish wiring is 11%. Read the explanation on every miss, and on the ones you guessed right: the exam rewords facts, so an answer letter is worth nothing while the reason behind it survives any wording. If your work also touches heating and cooling, the same motor, disconnect and Cal/OSHA logic reappears on the C-20 HVAC exam. Pair it with CSLB's free official C-10 study guide and the current California Electrical Code, and treat any guaranteed-pass promise as a warning sign.