Licensed Electrical Contractor Licensed Electrical Contractor Branch Circuit Calculations Questions and Answers 2 — Questions and Answers
Question 1: A 120V branch circuit supplies a 1,500W electric water heater. What is the minimum circuit ampere rating required per NEC Article 422?
- 15 amperes
- 20 amperes (Correct answer)
- 25 amperes
- 30 amperes
Correct answer: 20 amperes
A 1,500W load at 120V draws 12.5A, and since a fixed appliance requires 125% sizing, the minimum is 15.625A, requiring a 20A circuit.
Question 2: What is the maximum number of 180VA receptacle outlets permitted on a 20-ampere, 120-volt general-purpose branch circuit?
- 10
- 13 (Correct answer)
- 8
- 16
Correct answer: 13
A 20A circuit at 120V provides 2,400VA, and dividing by 180VA per outlet yields a maximum of 13 receptacle outlets.
Question 3: When calculating branch circuit loads for a commercial kitchen, a 5,000W electric oven connected to a 240V single-phase circuit draws how many amperes?
- 20.83 amperes (Correct answer)
- 24.0 amperes
- 26.04 amperes
- 30.0 amperes
Correct answer: 20.83 amperes
Dividing 5,000W by 240V yields approximately 20.83 amperes of current draw.
Question 4: Per NEC 210.11(C)(3), a dwelling unit requires at least how many 20-ampere small-appliance branch circuits for the kitchen and dining areas?
- 1
- 2 (Correct answer)
- 3
- 4
Correct answer: 2
The NEC requires a minimum of two 20-ampere small-appliance branch circuits serving kitchen countertop and dining area receptacles.
Question 5: A 14 AWG copper conductor on a 15-ampere branch circuit can safely supply a maximum continuous load of how many amperes?
- 12 amperes (Correct answer)
- 15 amperes
- 10 amperes
- 13.5 amperes
Correct answer: 12 amperes
A continuous load on a 15A branch circuit is limited to 80% of the rating, which equals 12 amperes.
Question 6: For a multiwire branch circuit supplying line-to-neutral loads, the neutral conductor carries the unbalanced current. If Line A draws 12A and Line B draws 8A, what current flows on the neutral?
- 20 amperes
- 4 amperes (Correct answer)
- 10 amperes
- 8 amperes
Correct answer: 4 amperes
On a multiwire branch circuit, the neutral carries only the difference between the two line currents, which is 12A minus 8A equaling 4A.
Licensed Electrical Contractor Licensed Electrical Contractor Branch Circuit Calculations Questions and Answers 2
A 120V branch circuit supplies a 1,500W electric water heater.
What is the minimum circuit ampere rating required per NEC Article 422?