IEC Conductors and Branch Circuits 2 — Questions and Answers
Question 1: What is the minimum branch circuit rating permitted for a single outlet on a household appliance circuit where the appliance nameplate rating is 12 amperes?
- 15 amperes (Correct answer)
- 20 amperes
- 25 amperes
- 30 amperes
Correct answer: 15 amperes
A 15-ampere branch circuit is sufficient when the single outlet serves an appliance rated at 12 amperes, since 12A does not exceed 80% of 15A for continuous loads.
Question 2: Which NEC table is used to determine the allowable ampacity of conductors in conduit based on temperature rating and insulation type?
- Table 310.16 (Correct answer)
- Table 220.12
- Table 250.66
- Table 430.52
Correct answer: Table 310.16
NEC Table 310.16 lists the allowable ampacities of insulated conductors rated up to 2000V in raceway, cable, or earth.
Question 3: A 20-ampere, 120-volt branch circuit supplies multiple receptacle outlets. What is the maximum load that may be connected continuously?
- 12 amperes
- 16 amperes (Correct answer)
- 20 amperes
- 24 amperes
Correct answer: 16 amperes
Continuous loads on a branch circuit must not exceed 80% of the circuit rating, so 80% of 20A = 16 amperes.
Question 4: What gauge is the smallest copper conductor permitted for branch circuits under NEC Article 210?
- 14 AWG (Correct answer)
- 12 AWG
- 10 AWG
- 8 AWG
Correct answer: 14 AWG
NEC Section 210.19 permits 14 AWG copper as the minimum conductor size for branch circuits, which corresponds to a 15-ampere rating.
Question 5: When conductors of different circuits are installed in the same raceway, which NEC adjustment factor must be applied?
- Temperature correction factor
- Bundling or fill derating factor (Correct answer)
- Voltage drop correction
- Demand factor
Correct answer: Bundling or fill derating factor
When more than three current-carrying conductors are in a raceway, NEC Table 310.15(C)(1) bundling derating factors must be applied to reduce allowable ampacity.
Question 6: Under the NEC, what is the maximum voltage permitted between conductors on a branch circuit supplying luminaires in a dwelling unit?
- 120 volts
- 150 volts (Correct answer)
- 240 volts
- 277 volts
Correct answer: 150 volts
NEC Section 210.6 limits branch circuits supplying luminaires in dwelling units to a maximum of 150 volts to ground.
Question 7: What is the purpose of a neutral conductor on a multiwire branch circuit?
- It carries fault current to ground
- It carries the unbalanced load current and completes the circuit (Correct answer)
- It provides equipment grounding
- It limits voltage drop on long runs
Correct answer: It carries the unbalanced load current and completes the circuit
The neutral on a multiwire branch circuit carries the difference (unbalanced) current between the two hot conductors and completes the return path.
IEC Conductors and Branch Circuits 2
What is the minimum branch circuit rating permitted for a single outlet on a household appliance circuit where the appliance nameplate rating is 12 amperes?