Licensed Electrical Contractor Branch Circuit Calculations 3 — Questions and Answers
Question 1: A 240V, single-phase branch circuit has a 30-ampere breaker. What is the maximum continuous load permitted on this circuit?
- 24 amperes (Correct answer)
- 30 amperes
- 37.5 amperes
- 20 amperes
Correct answer: 24 amperes
For a continuous load, the maximum permitted is 80% of the breaker rating: 30A × 0.80 = 24 amperes.
Question 2: Which NEC article specifically covers branch circuit requirements including ratings, outlet requirements, and conductor sizing?
- Article 210 (Correct answer)
- Article 230
- Article 215
- Article 220
Correct answer: Article 210
NEC Article 210 covers branch circuits, including their ratings, conductor requirements, and outlet placement.
Question 3: A bathroom branch circuit in a dwelling supplies two GFCI receptacles. Per NEC 210.11(C)(3), what is the minimum circuit rating required?
- 20 amperes (Correct answer)
- 15 amperes
- 30 amperes
- 10 amperes
Correct answer: 20 amperes
NEC 210.11(C)(3) requires at least one 20-ampere branch circuit for bathroom receptacle outlets.
Question 4: When calculating branch circuit loads for general lighting in a store, what unit load in VA per square foot does the NEC Table 220.12 specify?
- 3.3 VA/sq ft (Correct answer)
- 2 VA/sq ft
- 1.5 VA/sq ft
- 5 VA/sq ft
Correct answer: 3.3 VA/sq ft
NEC Table 220.12 assigns a unit load of 3.3 VA per square foot for store (retail) occupancies.
Question 5: A branch circuit conductor has a calculated voltage drop of 4.8V on a 120V circuit. What is the percentage voltage drop?
- 4% (Correct answer)
- 2.4%
- 3%
- 5%
Correct answer: 4%
Voltage drop % = (4.8V / 120V) × 100 = 4%, which exceeds the recommended 3% for branch circuits.
Question 6: What is the maximum overcurrent device rating permitted for a branch circuit supplying only lighting outlets per NEC 210.23?
- 20 amperes (Correct answer)
- 15 amperes
- 30 amperes
- 50 amperes
Correct answer: 20 amperes
NEC 210.23(A) permits lighting outlets on circuits rated up to 20 amperes when combined with cord-and-plug connected loads.
Question 7: A 15-ampere, 120V branch circuit supplies receptacles in an office. Using the NEC demand factor for general-purpose receptacles, what load in VA is assigned to each receptacle?
- 180 VA (Correct answer)
- 150 VA
- 200 VA
- 100 VA
Correct answer: 180 VA
NEC 220.14(I) assigns 180 VA per general-purpose receptacle outlet for load calculation purposes.
Licensed Electrical Contractor Branch Circuit Calculations 3
A 240V, single-phase branch circuit has a 30-ampere breaker.
What is the maximum continuous load permitted on this circuit?