Grounded and Ungrounded Systems
Chapter 2 of the National Electrical Code addresses wiring and protection and includes electrical grounding and bonding requirements. While many electrical systems today under 1,000V require grounding, there are a few justified reasons it is prohibited. In these cases, installing and operating the system ungrounded provides additional or increased protection. Ungrounded electrical systems provide a greater level of assurances of continuity of electrical power, even during a first, phase-to-ground fault event.
1. What is the maximum phase-to-ground voltage for a 480V three-phase delta system that is not grounded?
Correct Answer: 480
2. An electrical system or equipment not connected to ground or to a conducting body that extends the connection to ground is considered not grounded.
Correct Answer: True
3. As far as NFPA is concerned, the NEC is purely advisory but made available for private and public use. This could include adoption into law and for regulatory purposes and standardization activities such as insurance underwriting, building and facilities construction and management, and product testing and certification.
Correct Answer: True
4. A 480V three-phase, 3-wire, closed delta-connected system is always required to be grounded.
Correct Answer: False
5. Which of the following is not present when installing an ungrounded system?
Correct Answer: Grounded conductor
6. An AC system supplying premises wiring is required to be grounded where the maximum voltage to ground from any ungrounded conductor does not exceed 150V.
Correct Answer: True
7. All conductors and equipment covered by the NEC are required to be listed.
Correct Answer: False
8. The authority having jurisdiction for NEC enforcement is responsible for which of the following?
Correct Answer: All of the above
9. A phase-to-ground fault in an ungrounded system accidentally grounds the system and should activate required ground detectors.
Correct Answer: True
10. Isolated power systems installed in healthcare facilities are required to be installed and operated as _____ systems.
Correct Answer: Ungrounded
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