Minimum Requirements for Motors and More

Chapter 4 of the NEC, Equipment for General Use, includes the minimum requirements for equipment such as motors, transformers, appliances, heating equipment and more. According to Section 90.3, these rules are general in nature but could be amended by the specific requirements in chapters 5–7. Properly applying the NEC requires steady use and accurate navigation, so students of the Code are always learning.

1. Generally, what is the percentage for primary-only overcurrent protection for a transformer greater than 9A?

Correct Answer: 125%

2. Generally, when using primary plus secondary overcurrent protection for a 30-kVA transformer, what is the maximum percentage of the overcurrent protection on the primary?

Correct Answer: 250%

3. What is the current on the primary side of a 30-kVA, 480V, three-phase transformer with a 240V secondary?

Correct Answer: 36.1

4. An individual _____, single- or polyphase, identified by a single nameplate, unless otherwise indicated in Article 450, best defines which of the following?

Correct Answer: Transformer

5. Conductor overcurrent protection for supplying transformers is covered in Article 450.

Correct Answer: False

6. Conductors for capacitors shall be sized at not less than _____% of the rated current of the capacitor.

Correct Answer: 135

7. Potential transformers installed indoors or enclosed are required to be protected by which of the following?

Correct Answer: Primary fuses

8. Generally, dry-type transformers installed indoors and rated 112½ kVA or less shall have a separation of at least _____ from combustible material unless separated from the combustible material by a fire-resistant, heat-insulated barrier.

Correct Answer: 12 inches

9. How many amperes does a 100-horsepower, 460V, three-phase motor draw?

Correct Answer: 124

10. The rating of an overcurrent protective device for a capacitor shall be sized _____.

Correct Answer: As low as practicable