Licensed Electrical Contractor FREE 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-ampere 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 a metal water pipe is used as a grounding electrode, it must be supplemented by an additional electrode unless the pipe meets which condition?
- It is at least 10 feet in direct contact with the earth
- It is copper pipe with a minimum 1-inch diameter
- It is connected to a ground rod within 5 feet of entry
- No supplemental electrode is ever required with metal water pipes (Correct answer)
Correct answer: No supplemental electrode is ever required with metal water pipes
NEC 250.53(D)(2) always requires a supplemental electrode when using a metal underground water pipe as a grounding electrode.
Question 3: What is the maximum resistance to ground permitted for a single ground rod before a supplemental electrode must be installed?
- 10 ohms
- 15 ohms
- 20 ohms
- 25 ohms (Correct answer)
Correct answer: 25 ohms
Per NEC 250.53(A)(2), a single rod electrode must have a resistance of 25 ohms or less, otherwise a supplemental electrode is required.
Question 4: In a commercial building, where must the bonding jumper for a metal raceway containing service-entrance conductors be connected?
- At any convenient point along the raceway
- At each end and at every pull point (Correct answer)
- Only at the service equipment end
- Only at the meter base end
Correct answer: At each end and at every pull point
NEC 250.92(B) requires bonding of service raceways at each end and at all intervening points where access is available.
Question 5: What type of connection is prohibited for grounding electrode conductor splices unless it is an irreversible compression type?
- Bolted connections
- Exothermic welds
- Wire nut connectors (Correct answer)
- Listed split-bolt connectors
Correct answer: Wire nut connectors
NEC 250.64(C) prohibits splicing grounding electrode conductors unless the splice uses irreversible compression connectors, exothermic welding, or listed connectors.
Question 6: According to the NEC, what is the purpose of an equipment bonding jumper on the supply side of a service?
- To carry normal load current during operation
- To ensure an effective ground-fault current path for overcurrent device operation (Correct answer)
- To reduce voltage drop in branch circuits
- To provide a low-impedance path for lightning strikes only
Correct answer: To ensure an effective ground-fault current path for overcurrent device operation
Supply-side bonding jumpers ensure a low-impedance fault current path so that overcurrent protective devices can quickly clear ground faults.
Licensed Electrical Contractor FREE Licensed Electrical Contractor Grounding and Bonding Questions and Answers 2
What is the minimum size copper grounding electrode conductor required for a 400-ampere service per NEC Article 250?