CSLB Trade — Electrical (C-10) Practice Test
Practice stays free. The full CSLB Class C-10 — Electrical (Trade Exam) study guide is the material itself, taught start to finish — a downloadable PDF + EPUB you keep.
| Administering body | Contractors State License Board (CSLB), California Department of Consumer Affairs — exam delivered by PSI Services LLC |
|---|---|
| Questions | Not published by CSLB What we read and found nothing in: CSLB — Step 7: Studying for the Examination |
| Time limit | 210 minutes |
| Passing score | Not published by CSLB What we read and found nothing in: CSLB — Step 7: Studying for the Examination |
| Fees |
Source: CSLB — List of All CSLB Fees |
| Languages offered | English |
Frequently asked questions
How many CSLB C-10 Electrical trade questions are here?+
480+ original practice questions across the content areas of the C-10 electrical exam — Planning & Estimating, Services & Distribution, Branch Circuits & Wiring, Equipment & Systems, Testing & Troubleshooting, and Safety — with 2023 NEC / 2025 California Electrical Code references.
Is the C-10 trade exam separate from the Law & Business exam?+
Yes. To get a C-10 Electrical contractor license you must pass BOTH the Law & Business exam AND this C-10 trade exam. They are two separate exams, each about 3.5 hours at a PSI testing center.
Which code is the C-10 exam based on?+
The California Electrical Code (Title 24, Part 3), which adopts the National Electrical Code (NEC / NFPA 70) — currently the 2023 NEC. Expect code-lookup, load calculations, conductor/box/conduit sizing, grounding & bonding, and motor questions. A calculator is provided.
Are these the real CSLB exam questions?+
No. Every question is 100% original, written from public sources (the 2023 NEC / 2025 California Electrical Code and Cal/OSHA Title 8). We never copy real exam questions or paid prep material.
Can I study the C-10 material in Chinese or Spanish?+
Yes — PrepPass practice and study guides are in English, 中文 and Español. The official CSLB exam is offered in English (Spanish and translator accommodations may be available through CSLB); you can switch the question language to English any time to rehearse the wording you'll see at the test center.
Sample practice questions
A few real questions from this free bank, with full explanations. Use the practice tool above for the whole set.
- 1. Services & Distribution
A 200 A service uses 250 kcmil copper ungrounded service-entrance conductors. Per Table 250.66, what is the minimum copper grounding electrode conductor (GEC)?
- a.2 AWG copper
- b.1/0 AWG copper
- c.4 AWG copper
- d.6 AWG copper
Answer: a
Explanation: In Table 250.66 the row 'over 3/0 through 350 kcmil' requires a 2 AWG copper GEC, so 250 kcmil falls here. 4 AWG serves only 2/0-3/0, 6 AWG serves 1 or 1/0, and 1/0 is not required until conductors exceed 350 kcmil.
Source: 2023 NEC §250.66
- 2. Services & Distribution
What is the minimum depth of working space in front of a 120/240 V panelboard (Condition 1, exposed live parts on one side)?
- a.3.5 ft (1.07 m)
- b.4 ft (1.2 m)
- c.2 ft (0.6 m)
- d.3 ft (0.9 m)
Answer: d
Explanation: Per Table 110.26(A)(1), Condition 1 for systems 0-150 V to ground requires 3 ft (900 mm) of clear working depth. 2 ft is too shallow, and 3.5 ft/4 ft apply to higher-voltage or Condition 2/3 situations.
Source: 2023 NEC §110.26
- 3. Services & Distribution
For a 200 A service where the equipment and conductors are all rated for it, the conductor ampacity used for termination sizing is normally based on which temperature column?
- a.75 degrees C
- b.90 degrees C
- c.60 degrees C
- d.105 degrees C
Answer: a
Explanation: Per 110.14(C), for circuits over 100 A (or conductors larger than 1 AWG), terminations are generally rated 75 degrees C, so the 75 degrees C column of Table 310.16 is used unless equipment is listed otherwise. The 90 degrees C column is only for derating starting points, and 60 degrees C applies to smaller circuits.
Source: 2023 NEC §110.14
- 4. Branch Circuits & Wiring
The dedicated equipment space above a panelboard indoors extends from the top of the equipment to what height, or to the structural ceiling if lower?
- a.6 ft
- b.4 ft
- c.3 ft
- d.10 ft
Answer: a
Explanation: Section 110.26(E)(1)(a) requires the dedicated space above indoor electrical equipment such as panelboards to extend 6 ft above the equipment or to the structural ceiling, whichever is lower, kept clear of foreign piping and ducts. 3 and 4 ft are too little; 10 ft is more than the code requires.
Source: 2023 NEC §110.26(E)
- 5. Branch Circuits & Wiring
For a branch circuit rated 100 A or less, which temperature column must be used for conductor ampacity at the terminations unless the equipment or terminals are listed for a higher temperature?
- a.Any column may be used
- b.90°C
- c.60°C
- d.75°C
Answer: c
Explanation: Per 110.14(C)(1), for circuits 100 A or less the 60°C column applies unless the equipment/terminals are listed for 75°C (or higher). The 90°C column is never the termination limit, and you cannot freely choose the column.
Source: 2023 NEC §110.14(C)
- 6. Equipment & Systems
If a motor-compressor (rated-load 18 A) will not start on the 175% device, NEC 440.22(A) permits increasing the protection to a maximum of what value?
- a.300% = 54 A
- b.250% = 45 A
- c.225% = 40.5 A
- d.200% = 36 A
Answer: c
Explanation: NEC 440.22(A) allows an increase up to 225% of the rated-load current where the 175% device will not carry starting current: 18 x 2.25 = 40.5 A. 200%, 250%, and 300% are not the permitted ceilings for hermetic-compressor branch-circuit protection.
Source: 2023 NEC §440.22
- 7. Equipment & Systems
Cord-connected luminaires, hanging luminaires, and similar equipment shall not have parts located within what zone measured from the bathtub rim or shower threshold, unless marked for damp or wet locations?
- a.3 feet horizontally and 8 feet vertically
- b.6 feet horizontally and 10 feet vertically
- c.5 feet horizontally and 8 feet vertically
- d.3 feet horizontally and 6 feet vertically
Answer: a
Explanation: Section 410.10(D) prohibits such luminaire parts within a zone 3 feet horizontally and 8 feet vertically from the top of the bathtub rim or shower stall threshold, unless the luminaire is listed for damp or wet locations. This keeps ordinary fixtures out of reach of a person in the tub or shower.
Source: 2023 NEC §410.10
- 8. Planning & Estimating
How often is a new edition of the National Electrical Code, on which the California Electrical Code is based, normally published?
- a.Every 3 years
- b.Every 5 years
- c.Every 10 years
- d.Every 2 years
Answer: a
Explanation: The NEC is revised on a three-year cycle (e.g., 2017, 2020, 2023), and California adopts it with state amendments on a similar cycle. The other intervals do not match the code's revision schedule.
- 9. Planning & Estimating
The NEC is updated on a three-year cycle. The 2023 NEC directly follows which prior edition?
- a.2017 NEC
- b.There is no prior edition
- c.2014 NEC
- d.2020 NEC
Answer: d
Explanation: On the three-year cycle, the edition immediately before the 2023 NEC is the 2020 NEC. The 2017 and 2014 editions are earlier cycles, not the one directly preceding 2023.
- 10. Safety
Class 00 and Class 0 rubber insulating gloves are rated for maximum AC use voltages of approximately:
- a.250 volts and 500 volts
- b.5,000 volts and 10,000 volts
- c.500 volts and 1,000 volts respectively
- d.50 volts and 100 volts
Answer: c
Explanation: Class 00 gloves are rated to about 500V and Class 0 gloves to about 1,000V AC maximum use voltage. The 5,000/10,000V figures apply to higher classes, and 250/500V or 50/100V understate the ratings of these two glove classes.
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