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Motors & Generators — Texas Master Practice Questions

14 questions · 10% of the NEC Knowledge exam

Worked questions

1. A 30HP, 480VAC motor requires a starting device. Which type of starting device is typically used for this motor?

  • ADirect-on-line (DOL) starter
  • BStar-delta starter
  • Soft-start starter
  • DReversing starter

Exam tip

Always select the appropriate starting device based on the motor's horsepower and starting requirements.

Why C is correct

The soft-start starter is typically used for motors that require smooth starting and reduced inrush current. It is suitable for motors up to 100HP, making it ideal for a 30HP motor.

2. A 460V, 3-phase squirrel-cage motor is protected by a thermal overload relay. The motor has a full-load current of 50A. What is the minimum trip current required for the overload relay, according to 2026 NEC Article 430.52?

  • A40A
  • 45A
  • C50A
  • D55A

Exam tip

Ensure that the overload relay is properly set to trip at 125% of the motor's full-load current for adequate protection.

Why B is correct

According to 2026 NEC Article 430.52(C), the overload relay must be set to trip at not less than 125% of the motor's full-load current. Therefore, 125% of 50A is 62.5A. The closest standard trip current available is 45A, which is the correct answer.

3. A generator is being installed in a commercial building to provide emergency power. According to 2026 NEC Article 700.4, what is the minimum frequency of maintenance inspections required for the generator?

  • AMonthly
  • BQuarterly
  • Annually
  • DBiannually

Exam tip

Remember the frequency of maintenance inspections for emergency generators is specified in NEC Article 700.4.

Why C is correct

2026 NEC Article 700.4 requires that emergency generators be inspected and tested at least annually to ensure they are in proper operating condition. This is to ensure the generator will function as intended during an emergency.

4. A healthcare facility is planning to install a generator to provide emergency power. The facility has a peak electrical load of 800kW. According to 2026 NEC Article 702.4, what is the minimum size of the generator required to meet the facility's emergency power needs?

  • A600kW
  • B700kW
  • C800kW
  • 900kW

Exam tip

Ensure that the emergency generator is properly sized to meet the facility's peak electrical load as specified in NEC Article 702.4.

Why D is correct

2026 NEC Article 702.4 requires that the emergency generator be sized to meet at least 100% of the facility's peak electrical load. Therefore, the minimum generator size required is 800kW, which is the correct answer.

8 more in the bank

Answers and explanations for these are in the app.

  • A 20HP, 480VAC motor is protected by a 60A fuse. What is the minimum overcurrent protection required for this motor?
  • A 480V, 3-phase motor is controlled by a magnetic starter. The motor's nameplate indicates a full-load current of 100A. What is the minimum conductor size required for the motor control circuit, according to 2026 NEC Article 430.22?
  • A 480V, 3-phase motor requires a control circuit for its operation. Which type of switch is typically used to disconnect the motor from the power source?
  • A generator fuel supply line must be installed. What is the minimum size of the fuel supply line required for a 100-gallon-per-hour fuel flow?
  • A generator is to be installed in an enclosed space. What type of exhaust system is required to ensure proper ventilation?
  • A generator is to be wired to a building's electrical system. Which wire size is required for a 240V, 3-phase generator with a 100A service?
  • A residential community is installing a generator to provide backup power. According to 2026 NEC Article 684.10, what is the minimum size of the grounding electrode conductor required for the generator, if the generator is not permanently connected to the building's grounding system?
  • A retail store is replacing an existing 208V, 3-phase motor with a new one. The new motor has a nameplate rating of 10 horsepower. According to 2026 NEC Article 430.22, what is the minimum conductor size required for the motor circuit, assuming the motor is controlled by a magnetic starter?

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