IEC Conductors and Branch Circuits 3 — Questions and Answers
Question 1: A multiwire branch circuit in a dwelling unit must have a means to simultaneously disconnect all ungrounded conductors. Which NEC section requires this?
- 210.4(B) (Correct answer)
- 250.130(C)
- 310.15(B)
- 220.42
Correct answer: 210.4(B)
NEC Section 210.4(B) requires that each multiwire branch circuit in a dwelling unit be provided with a means to simultaneously disconnect all ungrounded conductors at the panelboard.
Question 2: What factor primarily determines the voltage drop on a branch circuit conductor run?
- Insulation color
- Conductor length and load current (Correct answer)
- Number of splices in the run
- Type of conduit used
Correct answer: Conductor length and load current
Voltage drop is primarily a function of conductor resistance (related to length and wire gauge) multiplied by the load current.
Question 3: Under NEC Article 210, which branch circuit type is required for bathroom receptacles in a dwelling unit?
- 15-ampere general-purpose circuit
- 20-ampere circuit dedicated to bathroom receptacles (Correct answer)
- 30-ampere circuit for high-load appliances
- Any GFCI-protected circuit is acceptable
Correct answer: 20-ampere circuit dedicated to bathroom receptacles
NEC Section 210.11(C)(3) requires at least one 20-ampere branch circuit dedicated to bathroom receptacles in dwelling units.
Question 4: When must tap conductors be protected by an overcurrent device at the point where they receive their supply?
- Always, with no exceptions
- Only when the tap exceeds 10 feet
- Exceptions in NEC 240.21 allow unprotected taps under specific length and ampacity conditions (Correct answer)
- Only when the tap feeds a motor
Correct answer: Exceptions in NEC 240.21 allow unprotected taps under specific length and ampacity conditions
NEC Section 240.21 provides tap conductor exceptions that allow conductors to be run without overcurrent protection at the source under defined length and ampacity rules.
Question 5: Which conductor insulation temperature rating allows the highest ampacity for a given AWG size in a dry location?
- 60°C (THHN)
- 75°C (THWN)
- 90°C (THHN/THWN-2) (Correct answer)
- 105°C (MTW)
Correct answer: 90°C (THHN/THWN-2)
A 90°C-rated insulation (such as THHN or THWN-2 in dry locations) permits the highest ampacity table values for a given conductor size.
Question 6: For a 240-volt, 2-wire branch circuit (no neutral), what conductors are present?
- Two hot conductors and one grounding conductor (Correct answer)
- One hot, one neutral, and one grounding conductor
- Two hot conductors only, with no grounding required
- One hot and one grounding conductor
Correct answer: Two hot conductors and one grounding conductor
A 240V 2-wire branch circuit has two ungrounded (hot) conductors and an equipment grounding conductor; no neutral is needed since neither leg is grounded.
Question 7: What is the minimum headroom required above the working space for electrical panelboards supplying branch circuits in commercial occupancies?
- 5.5 feet (1.7 m)
- 6.0 feet (1.8 m) or the height of the equipment, whichever is greater (Correct answer)
- 7.0 feet (2.1 m)
- 8.0 feet (2.4 m)
Correct answer: 6.0 feet (1.8 m) or the height of the equipment, whichever is greater
NEC Section 110.26(A)(3) requires a minimum headroom of 6.0 feet or the height of the equipment, whichever is greater, in front of electrical equipment.
IEC Conductors and Branch Circuits 3
A multiwire branch circuit in a dwelling unit must have a means to simultaneously disconnect all ungrounded conductors.
Which NEC section requires this?