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.
Created by: Michael Johnston
1. Which of the following circuits is required to be grounded?
A. 120-volt (V) lighting circuits
B. Circuits for cranes over Class III locations
C. Isolated power systems for healthcare facilities
D. Lighting systems as provided in 411.6(A)
2. A _______ system does not have a neutral point.
A. 120/240V, single-phase, 3-wire
B. 480Y/277V, three-phase, 4-wire, wye-connected, 208Y/120V, three-phase, 4-wire, wye-connected
C. 480V, three-phase, 3-wire, delta
D. 480Y/277V, three-phase, 4-wire, wye-connected
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?
A. A 480V, three-phase, 3-wire, delta system
B. Circuits for equipment within electrolytic cell working zones, as provided in Article 668
C. Isolated power systems in healthcare facilities covered by 517.61 and 517.160
D. Secondary circuits of lighting systems for pools, as covered in 680.23(A)(2)
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 to ground or grounded parts from the ungrounded (phase) conductors of an ungrounded system are often due to distributed leakage capacitance in the system.