Free CSLB NEC Electrical Code Exam Practice Test
Realistic 50-question practice exam with instant feedback and score reports.
About this practice exam
Free CSLB NEC Electrical Code Exam practice test with 50 realistic multiple-choice questions, instant grading, and explanations. Administered by PSI. Typical passing score is about 72%. Study with drill mode, category score reports, and a personalized review plan.
Exam format
- 50 multiple-choice practice questions
- Based on the PSI exam format
- Typical passing score: 72%
- Drill mode with instant feedback and explanations after each answer
Study tips
- Review the official exam content outline before your first practice run.
- Take the full practice exam once to establish a baseline score by category.
- Focus review on categories where you score below the passing threshold.
- Re-take missed questions in drill mode until you can explain each correct answer.
- Schedule the real exam only after consistent passing scores on practice tests.
Sample NEC Electrical Code practice questions
Try a few representative questions below. Each includes the correct answer and a short explanation — the same style you'll see in the full practice test.
- Question 1Service Entrance Conductors
A 120/240V, 3-phase, 4-wire, 200A service supplies a commercial building. The main service disconnect is rated at 200A. What is the minimum allowable size for the ungrounded service-entrance conductors, considering standard conductor ampacities and a maximum ambient temperature of 30°C (86°F)?
- A.250 kcmil THHN
- B.2/0 AWG THHN
- C.3/0 AWG THHN
- D.4/0 AWG THHN(Correct)
Explanation
According to NEC Table 310.16, the ampacity of 3/0 AWG THHN copper conductors at 75°C is 200A. However, for a 200A service, NEC 230.42(A)(1) requires conductors to have an ampacity not less than the maximum calculated load, and not less than the rating of the service overcurrent device. For a 200A service, 4/0 AWG THHN copper conductors (rated 230A at 75°C) are required to provide sufficient capacity above the 200A rating.
- Question 2Branch Circuits - Bathrooms
In a California dwelling unit, what is the maximum number of 15A, 120V branch circuits permitted to supply outlets in a single bathroom not exceeding 200 sq ft, considering the need for GFCI protection on all receptacles?
- A.One(Correct)
- B.As many as needed, provided they are GFCI protected
- C.Two
- D.Three
Explanation
NEC 210.11(C)(3)(1) requires at least one 20A (not 15A) branch circuit to supply bathroom receptacle outlets. This circuit can also supply other outlets in the dwelling unit, but it must supply ALL bathroom receptacle outlets. Therefore, only one dedicated circuit is mandated, and it must be 20A minimum.
- Question 3Feeder Sizing
A facility utilizes a 480/277V, 3-phase, 4-wire electrical system. A continuous load of 80A is supplied by a feeder protected by a 100A circuit breaker. What is the minimum size copper THWN conductors required for this feeder, assuming an ambient temperature of 40°C (104°F)?
- A.2/0 AWG
- B.1 AWG
- C.3/0 AWG
- D.1/0 AWG(Correct)
Explanation
The continuous load is 80A. NEC 210.19(A)(1) and 230.42(A)(1) require conductors to be sized at 125% of the continuous load, so 80A * 1.25 = 100A. The conductor ampacity must also be at least the rating of the overcurrent device, which is 100A. Consulting NEC Table 310.16 for THWN copper conductors at 75°C (column for wet/dry locations), 1/0 AWG has an ampacity of 150A, which is sufficient. However, considering the ambient temperature of 40°C, a correction factor of 0.88 must be applied (Table 310.15(B)(1)). So, the required ampacity is 100A / 0.88 = 113.6A. 1/0 AWG THWN has an ampacity of 150A at 75°C, which is greater than 113.6A.
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Frequently asked questions
How many questions are on this NEC Electrical Code practice test?
This practice test includes 50 multiple-choice questions designed to mirror the format and difficulty of the real CSLB NEC Electrical Code Exam.
Is this NEC Electrical Code practice test free?
Yes. You can start practicing for free. Create an account to save progress, track weak categories, and retake the exam.
Do I get explanations after each question?
Yes. In drill mode you see why the correct answer is right, why distractors are wrong, and practical examples where relevant.
How should I use this practice test to prepare?
Take the full exam under timed conditions, review missed questions by category, then focus study on your weakest sections before scheduling the real exam.
Does this replace official PSI materials?
No. Use this as a supplement alongside official candidate information bulletins, textbooks, and hands-on experience required for your license or certification.
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