Staying Grounded

The National Electrical Code includes requirements to ground electrical systems. It also contains information regarding electrical systems that are prohibited from being grounded and those systems that are permitted to be—but not required to be—grounded. If an electrical system is grounded as a requirement or by choice, all the rules related to grounded systems must be applied.

1. Which of the following circuits is required to be grounded?

120-volt (V) lighting circuits

Circuits for cranes over Class III locations

Isolated power systems for healthcare facilities

Lighting systems as provided in 411.6(A)

Correct Answer: 120-volt (V) lighting circuits

2. A _______ system does not have a neutral point.

120/240V, single-phase, 3-wire

480Y/277V, three-phase, 4-wire, wye-connected, 208Y/120V, three-phase, 4-wire, wye-connected

480V, three-phase, 3-wire, delta

480Y/277V, three-phase, 4-wire, wye-connected

Correct Answer: 480V, three-phase, 3-wire, delta

3. A 240V, three-phase, 3-wire, delta-connected system is required to be grounded.

True

False

Correct Answer: False

4. Which of the following circuits are permitted to be grounded?

A 480V, three-phase, 3-wire, delta system

Circuits for equipment within electrolytic cell working zones, as provided in Article 668

Isolated power systems in healthcare facilities covered by 517.61 and 517.160

Secondary circuits of lighting systems for pools, as covered in 680.23(A)(2)

Correct Answer: A 480V, three-phase, 3-wire, delta system

5. According to the NEC, is the phase-to-ground voltage (by definition) of the ungrounded conductors supplied by a 480V, three-phase, 3-wire, corner-grounded delta system?

120V

240V

277V

480V

Correct Answer: 480V

6. An AC system supplying premises wiring must be grounded where the maximum voltage to ground from any ungrounded conductor does not exceed 150V.

True

False

Correct Answer: True

7. A phase-to-ground fault in an ungrounded system unintentionally grounds the system and activates ground detectors.

True

False

Correct Answer: True

8. If a system is not grounded, only one conductor supplied by the system is intentionally grounded

True

False

Correct Answer: False

9. Ground detectors are not required for 240V, three-phase, ungrounded, delta-connected systems.

True

False

Correct Answer: False

10. The voltage readings to ground or grounded parts from the ungrounded (phase) conductors of an ungrounded system are often due to distributed leakage capacitance in the system.

True

False

Correct Answer: True

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Staying Grounded

1. Which of the following circuits is required to be grounded?

2. A _______ system does not have a neutral point.

3. A 240V, three-phase, 3-wire, delta-connected system is required to be grounded.

4. Which of the following circuits are permitted to be grounded?

5. According to the NEC, is the phase-to-ground voltage (by definition) of the ungrounded conductors supplied by a 480V, three-phase, 3-wire, corner-grounded delta system?

6. An AC system supplying premises wiring must be grounded where the maximum voltage to ground from any ungrounded conductor does not exceed 150V.

7. A phase-to-ground fault in an ungrounded system unintentionally grounds the system and activates ground detectors.

8. If a system is not grounded, only one conductor supplied by the system is intentionally grounded

9. Ground detectors are not required for 240V, three-phase, ungrounded, delta-connected systems.

10. The voltage readings&nbsp;to ground or grounded parts&nbsp;from the&nbsp;ungrounded (phase)&nbsp;conductors of an ungrounded system are often due to distributed leakage capacitance in the system.

10. The voltage readings to ground or grounded parts from the ungrounded (phase) conductors of an ungrounded system are often due to distributed leakage capacitance in the system.