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Wiring Methods — Texas Master Practice Questions

6 questions · 7% of the Calculations exam

Worked questions

1. A commercial building has a lighting load of 20,000 watts. The lighting fixtures are 120/277V. What is the minimum branch-circuit ampacity required?

  • A83.33A
  • 100A
  • C125A
  • D150A

Exam tip

When calculating branch-circuit ampacity for lighting, always multiply the total load by 1.25, as per NEC Article 210.6(A)(1).

Why B is correct

According to 2026 NEC Article 210.6(A)(1), the branch-circuit ampacity is determined by multiplying the total load in watts by 1.25. In this case, 20,000 watts x 1.25 = 25,000 watts. The 25,000 watts divided by 277V gives 90.3A, which rounds up to 100A. The other options are incorrect as they do not meet the calculated requirement.

2. A commercial building requires a 2-inch EMT raceway to carry 20 12AWG THHN conductors. What is the allowable fill of the raceway?

  • 60% of the raceway area
  • B70% of the raceway area
  • C80% of the raceway area
  • D90% of the raceway area

Exam tip

Remember to consider the fill requirements for both the conduit and the raceway as specified in NEC Article 318.

Why A is correct

According to 2026 NEC Article 318.6, the allowable fill for 12AWG conductors in a 2-inch EMT raceway is 60% of the raceway area. The other options are incorrect as they exceed the fill requirements specified in the NEC.

4. A residential circuit is to be wired with 10 AWG THWN-2 copper conductors. The conduit is 1-inch diameter. What is the allowable fill of the conduit?

  • A70% of the conduit area
  • B60% of the conduit area
  • 50% of the conduit area
  • D40% of the conduit area

Exam tip

Remember that conduit fill calculations are based on the size of the conduit and the number of conductors, as specified in NEC Article 318.

Why C is correct

According to 2026 NEC Article 318.8, the allowable fill for 10 AWG conductors in a 1-inch conduit is 50% of the conduit area. The other options are incorrect as they do not meet the requirements specified in the NEC.

5. A residential service panel has a 200A main disconnect. What is the minimum size of the overcurrent protection required for a 120V, 20A branch circuit?

  • 15A
  • B20A
  • C30A
  • D40A

Exam tip

When selecting overcurrent protection, ensure it does not exceed 125% of the branch circuit rating, as per NEC Article 210.11(A).

Why A is correct

According to 2026 NEC Article 210.11(A), the overcurrent protection for a 120V, 20A branch circuit must not exceed 125% of the branch circuit rating. In this case, 20A x 1.25 = 25A. The 15A breaker is the minimum size that meets this requirement. The other options are incorrect as they exceed the allowable overcurrent protection size.

6. An industrial installation requires a grounding conductor for a 600V, 3-phase, 4-wire system. The maximum current is 500A. What is the minimum size of the grounding conductor required?

  • A6AWG
  • 8AWG
  • C10AWG
  • D12AWG

Exam tip

Always refer to NEC Article 250.122(B) for the minimum size of grounding conductors in 3-phase, 4-wire systems.

Why B is correct

According to 2026 NEC Article 250.122(B), the grounding conductor must be at least 8AWG for a 600V, 3-phase, 4-wire system with a maximum current of 500A. The other options are incorrect as they do not meet the requirements specified in the NEC.

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