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Branch Circuit Conductors — Texas Master Practice Questions

23 questions · 16% of the NEC Knowledge exam

Worked questions

3. A healthcare facility has a 480V, 3-phase, 100A motor for a life support system. What is the minimum conductor size required for this motor circuit?

  • A6 AWG
  • 8 AWG
  • C10 AWG
  • D12 AWG

Exam tip

Special equipment such as life support systems often have specific code requirements for conductor sizing to ensure safety and reliability.

Why B is correct

According to 2026 NEC Article 680.41(A), the minimum conductor size for a 480V, 3-phase motor circuit for a life support system is 8 AWG. Larger conductors are not required for this application.

4. A 208-volt medical-equipment branch circuit has an established required conductor ampacity of 50 amperes. Its copper THWN-2 conductors run in a raceway with not more than three current-carrying conductors at 30°C ambient. The specified termination ampacity limit is 75°C, no correction or adjustment applies, and all other circuit requirements are satisfied. What is the smallest conductor meeting the required ampacity under 2026 NEC Table 310.16?

  • 8 AWG
  • B10 AWG
  • C12 AWG
  • D6 AWG

Where to look it up

https://www.mikeholt.com/instructor2/img/product/pdf/1769017155.pdf

Why A is correct

At 75°C, 10 AWG copper is rated 35 A and is too small; 8 AWG is rated 50 A. The original 12 AWG answer is not adequate for the stated 50 A requirement. A healthcare location alone does not determine this conductor size. The stated required ampacity and conditions govern this selection; they are not universal wire sizes for every circuit in that location. Source: Mike Holt Enterprises, Understanding the 2026 National Electrical Code, Volume 1, first printing January 2026, public sample pages 370–379, especially Table 310.16 on page 379. https://www.mikeholt.com/instructor2/img/product/pdf/1769017155.pdf

5. A residential kitchen circuit serves ten receptacles and has an established required conductor ampacity of 20 amperes. It uses copper THWN-2 conductors in a raceway, not more than three current-carrying conductors at 30°C ambient, and a specified 60°C termination ampacity limit. No correction or adjustment applies, and all other circuit requirements are satisfied. What is the smallest conductor meeting the ampacity requirement under 2026 NEC Table 310.16?

  • A10 AWG
  • 12 AWG
  • C14 AWG
  • D16 AWG

Where to look it up

https://www.mikeholt.com/instructor2/img/product/pdf/1769017155.pdf

Why B is correct

At the specified 60°C limit, 14 AWG copper is rated 15 A and is too small; 12 AWG is rated 20 A. Ten receptacles do not themselves increase this established conductor-ampacity requirement to 10 AWG. The original explanation also reversed the meaning of AWG size numbers. The stated required ampacity and conditions govern this selection; they are not universal wire sizes for every circuit in that location. Source: Mike Holt Enterprises, Understanding the 2026 National Electrical Code, Volume 1, first printing January 2026, public sample pages 370–379, especially Table 310.16 on page 379. https://www.mikeholt.com/instructor2/img/product/pdf/1769017155.pdf

6. A dedicated residential kitchen branch circuit has an established required conductor ampacity of 20 amperes. It uses copper THWN-2 conductors in a raceway at 30°C ambient, not more than three current-carrying conductors and a specified 60°C termination ampacity limit. No correction or adjustment applies, and all other circuit requirements are satisfied. Which is the smallest conductor meeting this ampacity requirement under 2026 NEC Table 310.16?

  • A10 AWG
  • 12 AWG
  • C14 AWG
  • D16 AWG

Where to look it up

https://www.mikeholt.com/instructor2/img/product/pdf/1769017155.pdf

Why B is correct

Use 12 AWG copper: it is rated 20 A in the specified 60°C column. The 15 A rating of 14 AWG is insufficient, while 10 AWG exceeds the needed size. A 90°C insulation rating does not remove the stated 60°C termination ampacity limit. The stated required ampacity and conditions govern this selection; they are not universal wire sizes for every circuit in that location. Source: Mike Holt Enterprises, Understanding the 2026 National Electrical Code, Volume 1, first printing January 2026, public sample pages 370–379, especially Table 310.16 on page 379. https://www.mikeholt.com/instructor2/img/product/pdf/1769017155.pdf

7. A 600-volt, three-phase substation feeder has an established required ampacity of 1200 amperes. It uses four identical parallel sets of copper THWN-2 phase conductors, each set in a separate raceway with not more than three current-carrying conductors at 30°C ambient. The specified termination ampacity limit is 75°C; all parallel-installation conditions are satisfied, and no correction, adjustment or other condition requires a larger size. What is the minimum conductor size in each set under 2026 NEC Table 310.16?

  • A250 kcmil
  • B300 kcmil
  • 350 kcmil
  • D400 kcmil

Where to look it up

https://www.mikeholt.com/instructor2/img/product/pdf/1769017155.pdf

Why C is correct

Each of the four equal sets must provide at least 1200 / 4 = 300 A. At 75°C, 300 kcmil copper provides 285 A per set, or 1140 A total, and fails. The next size, 350 kcmil, provides 310 A per set, or 1240 A total, and meets the requirement. This answer depends on four properly installed parallel sets; a single 350 kcmil conductor does not carry 1200 A. Source: Mike Holt Enterprises, Understanding the 2026 National Electrical Code, Volume 1, public sample pages 366–367 (310.10(G)) and 379 (Table 310.16). https://www.mikeholt.com/instructor2/img/product/pdf/1769017155.pdf

8. An outdoor lighting branch circuit has an established required conductor ampacity of 15 amperes. It uses wet-location-listed copper THWN-2 conductors in a raceway, with not more than three current-carrying conductors at 30°C ambient and a specified 60°C termination ampacity limit. No correction, adjustment or other condition requires a larger size. These are ordinary branch-circuit conductors, not fixture wires or taps. What is the smallest adequate conductor under 2026 NEC Table 310.16?

  • A12 AWG
  • 14 AWG
  • C16 AWG
  • D18 AWG

Where to look it up

https://www.mikeholt.com/instructor2/img/product/pdf/1769017155.pdf

Why B is correct

Choose 14 AWG copper, rated 15 A in the specified 60°C column. The 10 A rating of 16 AWG is too low; 12 AWG is rated 20 A and exceeds the needed size. Being outdoors does not by itself impose a 12 AWG minimum. The insulation and installation must still suit the wet environment. No special permission for an 18 AWG fixture wire or tap is part of this ordinary branch-circuit case. Source: Mike Holt Enterprises, Understanding the 2026 National Electrical Code, Volume 1, public sample pages 362–365 and 379. https://www.mikeholt.com/instructor2/img/product/pdf/1769017155.pdf

9. For an ordinary branch circuit supplying receptacles in a patient-care space, which wiring-method requirement is imposed by 2026 NEC 517.13(A)? No exception applies; the separate requirements of 517.13(B) must also be satisfied.

  • ANM cable with nonmetallic boxes solely because the conductors are insulated
  • BAny MC cable, even if its armor or sheath does not qualify as an equipment grounding conductor
  • CIndividual THWN-2 conductors without a qualifying metallic wiring method
  • A metal raceway or qualifying metallic cable system, with metal boxes, fittings and enclosures, whose metallic path qualifies as an equipment grounding conductor under 250.118

Where to look it up

https://steeltubeinstitute.org/wp-content/uploads/2025/12/2026-NEC-Changes.pdf

Why D is correct

D is correct: the metallic wiring method must itself qualify as an equipment grounding conductor, and its boxes, fittings and enclosures must be metal. An insulation designation such as THWN-2 does not establish that complete wiring method. Nor does the generic label MC or AC establish every assembly’s suitability for patient-care use. Compliance with this part alone does not waive 517.13(B) or other applicable requirements. Source: Steel Tube Institute, 2026 NEC Changes, page 19, 517.13(A). https://steeltubeinstitute.org/wp-content/uploads/2025/12/2026-NEC-Changes.pdf

10. An industrial plant has a 60 A, 480 VAC, 60 Hz motor branch circuit fed directly from the supply, without an adjustable-speed drive. The candidate listed conductors already meet all applicable ampacity, temperature, environmental and installation requirements. Considering voltage rating only, which is the lowest offered conductor voltage rating adequate for this circuit?

  • 600V
  • B1000V
  • C1500V
  • D2000V

Where to look it up

https://www.southwire.com/wire-cable/building-wire/simpull-sup-sup-thhn-thwn-2-copper/p/SPEC10000

Why A is correct

600 V, A, is the lowest offered rating that covers this 480 VAC application. Southwire’s SIMpull THHN/THWN-2 specification documents 600 V conductors for industrial branch-circuit use. Higher offered voltage ratings are not inherently unsuitable; they simply are not the lowest choice. The 60 A circuit rating does not establish a 1500 V insulation requirement, and ampacity must be evaluated separately. Sources: Southwire SPEC 10000, Application & Features: https://www.southwire.com/wire-cable/building-wire/simpull-sup-sup-thhn-thwn-2-copper/p/SPEC10000 ; Mike Holt, 2026 General Requirements, 110.3(B), listed equipment instructions: https://www.mikeholt.com/newsletters.php?action=display&letterID=3022

11. For new 120-volt, 15- or 20-ampere dwelling branch circuits, which choice names spaces not independently listed in the room-based AFCI requirement of 2026 NEC 210.12(B)? Assume each circuit serves only the stated space; the garage and crawl space are unfinished, nonhabitable and not used as any listed or similar room.

  • ABedrooms
  • BLiving rooms
  • Crawl spaces and garages under the stated conditions
  • DKitchens

Where to look it up

https://www.mikeholt.com/newsletters.php?action=display&letterID=3029

Why C is correct

Crawl spaces and garages are not independently listed; bedrooms, living rooms and kitchens are. This is not a blanket exemption for every circuit entering a garage or crawl space: a circuit serving a listed room still needs the required protection. GFCI rules are a separate check. Source: Mike Holt, GFCI and AFCI, based on the 2026 NEC, AFCI Protection for Dwelling Units, 210.12(B). https://www.mikeholt.com/newsletters.php?action=display&letterID=3029

12 more in the bank

Answers and explanations for these are in the app.

  • A 120/240-volt, 3-phase, 4-wire system is used in a commercial office building. What is the minimum conductor rating required for a 100-ampere load, according to 2026 NFPA 70 NEC?
  • A 30A branch circuit in a commercial building is protected by a 30A fuse. What is the maximum allowable conductor size for this circuit?
  • A 30A branch circuit is used for lighting in a commercial office building. Which type of overcurrent protection is required for this circuit?
  • A high-rise apartment building has a 200A, 120/240V branch circuit. Which type of overcurrent protection is required to prevent conductor overheating?
  • A hotel has a 20A, 120V branch circuit for kitchen appliances. Which type of overcurrent protection is required for this circuit?
  • A raceway in an office building has a total cross-sectional area of 100 square inches. What is the maximum allowable fill percentage, according to 2026 NFPA 70 NEC?
  • A residential kitchen requires a dedicated branch circuit for countertop appliances. Which conductor size is required for a 20A circuit, according to the 2026 NEC?
  • A retail store has a 20A branch circuit with a total load of 18A. What type of overcurrent protection is required for this circuit?
  • A retail store has a 30-ampere branch circuit with a 30-ampere circuit breaker. What is the maximum number of 15-ampere receptacles that can be safely installed on this circuit, according to 2026 NFPA 70 NEC?
  • A school district is installing a new branch circuit for computer labs. Which type of conductor protection is required to prevent physical damage in the floor raceway?
  • An industrial facility has a 100A, 480V motor that operates continuously. What is the minimum conductor size required for this motor circuit?
  • In an industrial facility, all electrical equipment must be bonded to the grounding system. Which of the following is the correct method for bonding electrical equipment, according to 2026 NFPA 70 NEC?

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