EETC Grounding Systems 4 — Questions and Answers
Question 1: What is the minimum length of a ground rod electrode required by the NEC?
- 4 feet
- 6 feet
- 8 feet (Correct answer)
- 10 feet
Correct answer: 8 feet
NEC 250.52(A)(5) requires ground rod electrodes to be at least 8 feet in length and must be installed to make contact with the soil.
Question 2: An equipment grounding conductor run in a conduit with ungrounded conductors must be sized based on which NEC table?
- Table 250.66
- Table 250.102(C)(1)
- Table 250.122 (Correct answer)
- Table 310.15
Correct answer: Table 250.122
NEC Table 250.122 is used to size equipment grounding conductors based on the ampere rating of the overcurrent device protecting the circuit.
Question 3: What is 'touch potential' in grounding system analysis?
- The voltage between two ground rods
- The voltage between a grounded structure and a point on the earth's surface within arm's reach (Correct answer)
- The voltage drop across the grounding electrode conductor
- The difference in potential between two electrodes in series
Correct answer: The voltage between a grounded structure and a point on the earth's surface within arm's reach
Touch potential is the voltage difference between a grounded metallic structure and a point on the earth's surface that a person standing nearby could simultaneously contact.
Question 4: Which of the following is required when a grounding electrode conductor is run exposed along a wall?
- It must be painted green
- It must be protected from physical damage where subject to it (Correct answer)
- It must be in a metal conduit at all times
- It must be a minimum of 1/0 AWG
Correct answer: It must be protected from physical damage where subject to it
NEC 250.64(B) requires that a grounding electrode conductor exposed to physical damage be protected by conduit, armor, or other approved means.
Question 5: What does the term 'bonding' mean in the context of NEC grounding requirements?
- Connecting equipment to a grounding electrode
- Permanently joining metallic parts to form an electrically conductive path (Correct answer)
- Installing a ground rod next to metal piping
- Connecting the neutral to the equipment ground at a subpanel
Correct answer: Permanently joining metallic parts to form an electrically conductive path
Bonding is the permanent joining of metallic parts to ensure electrical continuity and the ability to safely conduct any fault current.
Question 6: In a corner-grounded delta system, which conductor is grounded?
- The center tap of one winding
- One phase conductor (Correct answer)
- The neutral conductor
- The equipment grounding conductor only
Correct answer: One phase conductor
In a corner-grounded delta system, one of the three phase conductors is connected to ground, which must be identified with green color coding.
Question 7: What is the minimum size copper conductor permitted for a grounding electrode conductor where connected to a rod, pipe, or plate electrode?
- 10 AWG
- 8 AWG
- 6 AWG (Correct answer)
- 4 AWG
Correct answer: 6 AWG
Per NEC 250.66(A), the grounding electrode conductor need not be larger than 6 AWG copper when the electrode is a rod, pipe, or plate.
EETC Grounding Systems 4
What is the minimum length of a ground rod electrode required by the NEC?