Specific System Markings
Requirements for grounding electrical systems are provided in Section 250.20. Section 250.21 includes requirements for electrical systems permitted, but not required, to be grounded. All applicable National Electrical Code rules must be applied. There are specific marking requirements for ungrounded electrical systems and those grounded in a manner that produces a high leg of the system. The marking requirements are generally intended to warn qualified personnel and occupants to the system’s uniqueness and stress exercising additional precautionary measures.
1. The high leg of a grounded electrical system is required to be marked with the color _____ or by other effective means.
Correct Answer: Orange
2. An ungrounded electrical system operating at 480V is not required to have ground detection.
Correct Answer: False
3. An isolated power system for a hospital operating room is an example of a system where the secondary circuits of such systems are permitted to be grounded but not required to be grounded.
Correct Answer: False
4. If an electrical system can be grounded so that maximum voltage to ground from any of the ungrounded conductors does not exceed _____, then the system is required to be grounded.
Correct Answer: 150
5. The high leg of a three-phase, 4-wire, delta-connected system is required to be the “B” phase of the system, except for within metering equipment.
Correct Answer: True
6. A switchboard, panelboard or switchgear that contains a three-phase, 4-wire, delta-connected system high leg must be marked with which of the following:
Correct Answer: Caution _____ phase has _____ volts to ground
7. If an electrical system is grounded, a connection to _____ is required.
Correct Answer: Earth
8. A 480V, three-phase, 3-wire, delta system is an example of a system that is not required to be grounded but is permitted to be grounded.
Correct Answer: True
9. The grounded conductor of an electrical system is generally and commonly identified by which of the following colors:
Correct Answer: Either A or B
10. An ungrounded system shall be marked at the source or first disconnecting means with which of the following:
Correct Answer: Caution: ungrounded system operating at _____ volts between conductors
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