The minimum number of 120-volt, 15-amp lighting circuits required for a dwelling with a 70 × 30 ft floor area is

• A. 2
• B. 3
• C. 5
• D. 4

Answer: (D)

The main idea is to estimate the dwelling’s general lighting load and see how many 15A, 120V circuits are needed to carry that load.

For dwelling lighting, the code uses about 3 volt-amperes per square foot. The floor area is 70 ft by 30 ft, which is 2100 ft². So the total lighting load is 2100 × 3 = 6300 VA.

Each 120V, 15A circuit can carry up to 120 × 15 = 1800 VA. Dividing the total load by the per-circuit capacity gives 6300 ÷ 1800 ≈ 3.5. You must round up to a whole circuit, so four circuits are needed.

So, four lighting circuits is the minimum. (This ignores other loads like receptacles or specialty systems, which would add more circuits if accounted for.)