Licensed Electrical Contractor Licensed Electrical Contractor Grounding and Bonding Questions and Answers 2 — Questions and Answers
Question 1: What is the minimum size copper grounding electrode conductor required for a 400-amp service per NEC Article 250?
- 1/0 AWG (Correct answer)
- 2/0 AWG
- 3/0 AWG
- 4/0 AWG
Correct answer: 1/0 AWG
NEC Table 250.66 requires a minimum 1/0 AWG copper grounding electrode conductor for services up to 500 kcmil.
Question 2: When using a concrete-encased electrode (Ufer ground), what is the minimum length of bare copper conductor that must be encased in the concrete?
- 10 feet
- 20 feet (Correct answer)
- 30 feet
- 40 feet
Correct answer: 20 feet
NEC 250.52(A)(3) requires at least 20 feet of bare copper conductor encased in concrete for a Ufer ground.
Question 3: What is the primary purpose of equipment bonding jumpers in an electrical system?
- To carry normal operating current
- To ensure electrical continuity and conductivity between metal parts (Correct answer)
- To provide a path for neutral current
- To reduce voltage drop in branch circuits
Correct answer: To ensure electrical continuity and conductivity between metal parts
Equipment bonding jumpers ensure electrical continuity between metal parts so fault current can flow and protective devices can operate.
Question 4: Per NEC 250.104, what metal piping system within a building must be bonded to the electrical service grounding system?
- Only copper water piping
- Only gas piping
- Interior metal water piping (Correct answer)
- All HVAC ductwork regardless of material
Correct answer: Interior metal water piping
NEC 250.104(A) requires interior metal water piping to be bonded to the service equipment enclosure or grounding electrode conductor.
Question 5: What is the maximum resistance to ground allowed for a single rod, pipe, or plate grounding electrode before a supplemental electrode is required?
- 5 ohms
- 10 ohms
- 15 ohms
- 25 ohms (Correct answer)
Correct answer: 25 ohms
NEC 250.53(A)(2) requires a supplemental electrode if a single rod, pipe, or plate electrode exceeds 25 ohms resistance to ground.
Question 6: In a separately derived system such as a transformer, where must the bonding jumper be installed?
- At the main service panel only
- At any convenient point in the system
- At the source of the separately derived system (Correct answer)
- At the nearest subpanel downstream
Correct answer: At the source of the separately derived system
NEC 250.30(A)(1) requires the system bonding jumper to be installed at the source of the separately derived system.
Licensed Electrical Contractor Licensed Electrical Contractor Grounding and Bonding Questions and Answers 2
What is the minimum size copper grounding electrode conductor required for a 400-amp service per NEC Article 250?