Licensed Electrical Contractor Branch Circuit Calculations 2 — Questions and Answers
Question 1: A 20-ampere branch circuit serves a small appliance circuit in a kitchen. What is the maximum load, in watts, allowed on this circuit at 120V using the 80% rule?
- 1,920 watts (Correct answer)
- 2,400 watts
- 1,600 watts
- 2,000 watts
Correct answer: 1,920 watts
The 80% continuous load rule limits a 20A circuit at 120V to 20A × 0.80 × 120V = 1,920 watts.
Question 2: Per NEC Article 210, how many small appliance branch circuits are required for the kitchen countertop receptacle outlets in a dwelling unit?
- At least two 20-ampere circuits (Correct answer)
- At least one 15-ampere circuit
- At least three 20-ampere circuits
- At least one 20-ampere circuit
Correct answer: At least two 20-ampere circuits
NEC 210.11(C)(1) requires at least two 20-ampere small appliance branch circuits for kitchen countertop receptacles.
Question 3: A branch circuit conductor must be sized so that voltage drop does not exceed what percentage for branch circuits per NEC recommendations?
- 3% (Correct answer)
- 5%
- 2%
- 10%
Correct answer: 3%
The NEC recommends (informational note) that voltage drop on a branch circuit not exceed 3% for best performance.
Question 4: What is the minimum wire gauge (AWG) required for a 20-ampere, 120V branch circuit using copper conductors?
- 12 AWG (Correct answer)
- 14 AWG
- 10 AWG
- 8 AWG
Correct answer: 12 AWG
NEC 240.4(D) requires 12 AWG copper conductors for circuits protected by 20-ampere overcurrent devices.
Question 5: A branch circuit supplies a 7.5 kVA, 240V single-phase motor load. What is the full-load current of this motor?
- 31.25 amperes (Correct answer)
- 62.5 amperes
- 15.6 amperes
- 21.7 amperes
Correct answer: 31.25 amperes
I = kVA × 1000 / V = 7,500 / 240 = 31.25 amperes for a single-phase load.
Question 6: What NEC section governs the maximum number of outlets permitted on a branch circuit in a commercial occupancy?
- There is no NEC limit on number of outlets; load calculations govern (Correct answer)
- NEC 210.24 limits outlets to 10 per circuit
- NEC 210.19 limits outlets to 13 per circuit
- NEC 210.11 limits outlets to 8 per circuit
Correct answer: There is no NEC limit on number of outlets; load calculations govern
The NEC does not set a maximum number of outlets per branch circuit; the total connected load determines the circuit size.
Question 7: For a branch circuit supplying a continuous load, the overcurrent protective device must be rated at no less than what percentage of the continuous load?
- 125% (Correct answer)
- 80%
- 100%
- 115%
Correct answer: 125%
NEC 210.20(A) requires the overcurrent device to be rated at not less than 125% of the continuous load.
Licensed Electrical Contractor Branch Circuit Calculations 2
A 20-ampere branch circuit serves a small appliance circuit in a kitchen.
What is the maximum load, in watts, allowed on this circuit at 120V using the 80% rule?