C-10 Electrical exam questions, with answers

10 practice questions for the CSLB Electrical trade exam, each with the answer, a plain explanation and the source it rests on.

From our free C-10 test · Updated 14 October 2026

The C-10 exam has 5 sections. The questions below are grouped by section, with the share of the exam each one carries. Read the question, pick an answer, then open “Show the answer”. The other questions of the free test, scored section by section, are in the free 25-question C-10 test.

Planning and Estimating · 28% of the exam

Existing system evaluation; plan and specification interpretation; electrical calculations; code requirements; material selection; energy production and storage project planning (photovoltaic, wind, generators, batteries, capacitors).

1. The specifications for an office tenant improvement call for two empty spare conduits from the new panelboard into the ceiling space and a panelboard with more spaces than the load calculation needs. The tenant asks why the engineer specified more than the minimum. Which statement from Article 90 explains this planning choice?

1. Plans with room in raceways, spare raceways and extra spaces let the system grow with future loads
2. The Code requires every new panelboard to leave 25 percent of its spaces empty for future circuits
3. Code-minimum sizing already includes room for future loads, so the spares only please the owner
4. Spare raceways are needed only where the inspector orders them by special permission under 90.4

2. Your C-10 company takes a one-day job adding two circuits in a house. To save money, you plan to send a laborer who is neither a certified electrician nor a registered electrician trainee, since the job is so short. According to the DIR Electrician Certification Unit, may he do this electrical work?

1. No; certification applies however short the job is, unless he is a supervised trainee
2. Yes; certification applies only to jobs that last longer than one week on the same site
3. Yes, if the C-10 license holder pulls the permit and checks the work when it is done
4. Yes; certification applies only to new construction, not to work in existing houses

Rough Wiring · 27% of the exam

System layout; clearance and accessibility requirements; raceway and panel installation; wire and equipment installation; grounding and bonding; energy production and storage rough wiring.

3. A new single-family home has a laundry room with a washer receptacle and a utility sink. Which plan for the washer receptacle meets 210.11(C)(2) and 210.8(A)?

1. On a 15-A general-purpose circuit shared with the hallway, protected by a GFCI device
2. On a 20-A laundry circuit that also feeds the room's ceiling light, protected by a GFCI
3. On a 20-A laundry circuit that serves no other outlets, protected by a GFCI device
4. On a 20-A laundry circuit that serves no other outlets, with no GFCI for one appliance

4. On a house remodel, the owner suggests four places for a new 100-A subpanel. Which location does 240.24 allow?

1. On a hallway wall, with clear working space in front of it
2. Inside the bedroom clothes closet, behind the hanging rod
3. On the wall of the main bathroom, beside the linen shelves
4. On the stairwell wall, directly over the steps of the stair

Finish Wiring and Trim · 11% of the exam

Finish device placement and installation; motor and equipment installation; wire and equipment labeling; trims and sealants; energy production and storage finish wiring.

5. At a commercial car wash, a 20-A, 125-V receptacle is mounted on a bay wall that is cleaned routinely with high-pressure spray. Under the 406.9(B)(1) exception for receptacles subject to routine high-pressure spray washing, what is required?

1. A flush plate with no cover; the receptacle must instead be a GFCI listed WR
2. A cover weatherproof with the plug removed; a standard non-WR receptacle is acceptable
3. Any cover at all; the spray-washing exception drops the weatherproof cover rule
4. A cover weatherproof with the plug removed; the receptacle must still be listed WR

6. You install a permanently connected 100-W towel warmer in a bathroom. It has no switch of its own, and its branch-circuit breaker is in a panel in the garage, out of sight. Under 422.31, may that breaker serve as the warmer's disconnecting means?

1. No; every permanently connected appliance needs a disconnect within sight of the appliance
2. Yes, but only if a lock-off device that stays in place is added to the breaker
3. Yes; the branch-circuit breaker may be the disconnect for appliances of 300 VA or less
4. No; the breaker may serve as the disconnect only for cord-and-plug appliances

Startup, Troubleshooting, and Maintenance · 16% of the exam

System energizing and testing; common electrical problems; location, repair, and replacement of inoperable electrical wires and components; selection and use of electrical testing equipment; energy production and storage system performance.

7. You are commissioning a home's Enphase system with IQ Battery 5P and need to turn the PV production off for one step of the start-up. Per Enphase's best-practices brief for this system, where should you shut off the PV circuits?

1. At each microinverter's connector on the roof, unplugging them one at a time
2. At the IQ Combiner or PV subpanel, not with the breaker inside the IQ System Controller
3. With the PV breaker inside the IQ System Controller, since it is the quickest point to reach
4. At the main service breaker, so the gateway and the batteries shut down together

8. You will take voltage readings on the underground line that runs from a farmhouse's service to a well pump out in the field. Per Fluke's meter-safety guide, which measurement category should your meter be rated for?

1. CAT I
2. CAT II
3. CAT IV
4. CAT III

Safety · 18% of the exam

Lockout/tagout procedures; personal protective equipment (PPE); tools and equipment; hazardous materials and job site environments.

9. On a remote job, your crew runs corded tools from a small portable generator: a two-wire, single-phase unit rated 4 kW whose circuit conductors are insulated from the frame and all grounded surfaces. Under Title 8 §2405.4(c), do the generator's 120-V, 20-A receptacles need GFCI protection?

1. No; a two-wire generator like this, rated 5 kW or less, is exempt from the GFCI rule
2. Yes; that exemption covers only generators rated 2 kW or less with a bonded frame
3. Yes; on construction sites the GFCI rule covers all generator receptacles in use
4. No; the GFCI rule covers only receptacles that are part of the permanent wiring

10. Your crew will service flooded lead-acid batteries with ordinary vent caps, kept on charge on open racks in a UPS room at an industrial plant where workers can reach them. Under Title 8 §5185, what must be provided in this battery area?

1. A posted area where smoking is allowed at least 25 ft from the racks
2. Battery racks of bare steel so that each battery is bonded to ground
3. Metal stirring rods kept beside the racks for mixing the electrolyte
4. Facilities for quick drenching or flushing of the eyes and body

Where to go from here

How the license works, from experience to fees: how to get a C-10 license. Everything about the course: the C-10 exam page.

Questions from our free C-10 test, written from CSLB License Examination Study Guide, Electrical (C-10), form 13E-10 (03-2026), for examinations scheduled on or after June 1, 2024. CSLB notes that the percentages are approximate. Reviewed 14 October 2026. Study guidance only; we are not affiliated with CSLB or PSI.