IEC Grounding and Bonding 2 — Questions and Answers
Question 1: What is the minimum size copper equipment grounding conductor required for a 60-ampere circuit per NEC Table 250.122?
- #10 AWG
- #8 AWG (Correct answer)
- #6 AWG
- #4 AWG
Correct answer: #8 AWG
NEC Table 250.122 requires a minimum #8 AWG copper equipment grounding conductor for circuits rated up to 60 amperes.
Question 2: Which NEC article specifically covers grounding and bonding requirements?
- Article 200
- Article 230
- Article 250 (Correct answer)
- Article 300
Correct answer: Article 250
NEC Article 250 contains all general requirements for grounding and bonding of electrical installations.
Question 3: A main bonding jumper in a service panel connects which two components?
- The neutral bar to the grounding electrode
- The equipment grounding bar to the grounding electrode conductor
- The neutral (grounded) conductor to the equipment grounding conductor (Correct answer)
- The service entrance conductors to the grounding electrode system
Correct answer: The neutral (grounded) conductor to the equipment grounding conductor
The main bonding jumper connects the neutral (grounded) conductor to the equipment grounding conductor at the service entrance.
Question 4: When is it permitted to connect the neutral bar and ground bar together in a subpanel?
- When the subpanel is located in the same building as the main panel
- When the subpanel is fed by a 3-wire feeder
- Never — neutral and ground must always be separate in subpanels (Correct answer)
- When the feeder originates from a separately derived system
Correct answer: Never — neutral and ground must always be separate in subpanels
In a subpanel (remote distribution panel), the neutral and equipment grounding conductors must always be kept separate to prevent objectionable current on grounding paths.
Question 5: What is the purpose of a grounding electrode system?
- To carry fault current back to the source during a short circuit
- To establish a reference voltage to earth and limit voltage imposed by lightning or line surges (Correct answer)
- To provide a low-impedance path for equipment grounding conductors
- To bond all metallic water pipes in a building together
Correct answer: To establish a reference voltage to earth and limit voltage imposed by lightning or line surges
The grounding electrode system establishes a reference to earth potential and limits voltages imposed by lightning, line surges, or unintentional contact with higher-voltage lines.
Question 6: Per NEC 250.68(A), a grounding electrode conductor must be connected to the grounding electrode in what manner?
- By pressure connectors, clamps, or other listed means (Correct answer)
- Only by exothermic welding
- By mechanical lugs rated for aluminum or copper
- Only by listed irreversible compression connectors
Correct answer: By pressure connectors, clamps, or other listed means
NEC 250.68(A) permits the grounding electrode conductor to be connected using listed pressure connectors, clamps, or other listed means; exothermic welding is not the only method.
Question 7: If a metal underground water pipe is used as a grounding electrode, what is the minimum buried length required by NEC 250.52(A)(1)?
- 5 feet
- 8 feet
- 10 feet (Correct answer)
- 20 feet
Correct answer: 10 feet
NEC 250.52(A)(1) requires a metal underground water pipe electrode to have at least 10 feet of direct burial contact with the earth.
IEC Grounding and Bonding 2
What is the minimum size copper equipment grounding conductor required for a 60-ampere circuit per NEC Table 250.122?