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Feeders — Texas Master Practice Questions

14 questions · 10% of the NEC Knowledge exam

Worked questions

1. A 200A feeder is supplying a new residential building. Which type of overcurrent protection device is required at the main service panel, according to 2026 NEC 240.21(A)?

  • ASingle-pole circuit breaker
  • Double-pole circuit breaker
  • CGround-fault circuit interrupter (GFCI)
  • DArc-fault circuit interrupter (AFCI)

Exam tip

Always check for the specific requirements for feeders to dwelling units, as they can differ from general requirements.

Why B is correct

According to 2026 NEC 240.21(A), a double-pole circuit breaker is required for feeders to a dwelling unit to prevent the possibility of a fire from spreading between the phases of a 240-volt, 3-wire, single-phase service. Single-pole circuit breakers are not sufficient for this purpose.

4. A high-rise apartment building is to be served by a 400A, 480V, 3-phase feeder. What is the minimum size of the grounding electrode conductor required according to 250.66(A)(1)?

  • A1/0 AWG
  • 2/0 AWG
  • C3/0 AWG
  • D4/0 AWG

Exam tip

Always refer to 250.66(A)(1) for the minimum size of grounding electrode conductors.

Why B is correct

According to 250.66(A)(1), the minimum size of the grounding electrode conductor required for a 400A, 480V, 3-phase feeder is 2/0 AWG. The other options are larger and not necessary for this application.

6. In a commercial building, a 400A feeder is supplying a lighting circuit. Which type of overcurrent protection is required for this circuit, according to 2026 NEC 210.11(A)?

  • AFused disconnect
  • Circuit breaker
  • CGround-fault circuit interrupter (GFCI)
  • DArc-fault circuit interrupter (AFCI)

Exam tip

Remember that circuit breakers are the standard overcurrent protection for feeders in commercial buildings.

Why B is correct

According to 2026 NEC 210.11(A), a circuit breaker is required for all branch circuits and feeders. Fused disconnects are not required for feeders in commercial buildings.

8. Which type of overcurrent protection is required for a 480V, 3-phase feeder in a commercial building according to 240.4(A)?

  • ASingle-pole fuse
  • Double-pole fuse
  • CGround-fault circuit interrupter (GFCI)
  • DNone, as it is a 3-phase system

Exam tip

Remember that 3-phase systems require double-pole protection.

Why B is correct

According to 240.4(A), a double-pole fuse or circuit breaker is required for a 480V, 3-phase feeder. Single-pole fuses are not suitable for 3-phase systems, and GFCIs are not required for feeders.

6 more in the bank

Answers and explanations for these are in the app.

  • A high-rise building is being constructed, and a 480V, 3-phase, 4-wire feeder is being installed. What is the grounding requirement for this feeder, according to 2026 NEC 250.184(A)?
  • A new 120/208V, 3-phase, 4-wire feeder is being installed for an industrial facility. The maximum load is 500kW. What is the minimum conductor size required, according to 2026 NEC 310.16(B)(1)?
  • A public utility is planning to install a new 12kV, 3-phase, 4-wire feeder. Which conductor material is required, according to 2026 NEC 310.12(A)?
  • A residential building is to be served by a 200A feeder. The maximum number of 20A, 120/240V branch circuits that can be supported is:
  • A retail store is to be served by a 100A, 120/240V single-phase feeder. What type of overcurrent protection is required for this feeder according to 240.4(B)(1)?
  • A suburban area is planning to install a new 120/240V, 3-phase, 4-wire feeder. What is the minimum spacing requirement between feeders, according to 2026 NEC 230.6(B)?

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