NCCER Electrical Grounding & Bonding 1 — Questions and Answers
Question 1: What is the primary purpose of an equipment grounding conductor (EGC) in an electrical circuit?
- To carry normal load return current back to the source
- To provide a low-impedance fault current path so overcurrent devices can operate (Correct answer)
- To reduce voltage drop on long circuit runs
- To balance the load between phase conductors
Correct answer: To provide a low-impedance fault current path so overcurrent devices can operate
EGCs provide a low-impedance path for fault current, enabling overcurrent protective devices to clear the fault quickly and safely.
Question 2: According to NEC Table 250.122, what is the minimum copper equipment grounding conductor size for a branch circuit protected by a 20-ampere overcurrent device?
- 14 AWG
- 12 AWG (Correct answer)
- 10 AWG
- 8 AWG
Correct answer: 12 AWG
NEC Table 250.122 requires a minimum 12 AWG copper EGC for circuits protected by overcurrent devices rated up to 20 amperes.
Question 3: Per NEC 250.56, when must a supplemental ground rod be added to a grounding electrode system?
- When the service is rated over 200 amperes
- When the soil is sandy or rocky
- When a single rod electrode has a measured resistance exceeding 25 ohms to earth (Correct answer)
- When the building has more than two stories
Correct answer: When a single rod electrode has a measured resistance exceeding 25 ohms to earth
NEC 250.56 requires a supplemental electrode if the resistance of a single rod to earth exceeds 25 ohms.
Question 4: What is the minimum length required for a driven rod electrode per NEC 250.52(A)(5)?
- 4 feet
- 6 feet
- 8 feet (Correct answer)
- 10 feet
Correct answer: 8 feet
NEC 250.52(A)(5) specifies that rod electrodes must be at least 8 feet (2.44 m) in length.
Question 5: What is the key difference between a grounded conductor and an equipment grounding conductor?
- They are functionally the same and can be interchanged
- A grounded conductor carries normal load return current; an EGC carries fault current (Correct answer)
- An EGC carries normal load current; a grounded conductor carries fault current
- A grounded conductor is only used in three-phase systems
Correct answer: A grounded conductor carries normal load return current; an EGC carries fault current
The grounded conductor (neutral) carries normal return current under load, while the EGC provides a fault current path during a ground fault.
Question 6: Which of the following qualifies as an acceptable grounding electrode under NEC 250.52(A)(1)?
- A plastic underground water pipe
- A metal underground water pipe with at least 10 feet in direct contact with the earth (Correct answer)
- A steel fence post driven 4 feet into the ground
- A PVC conduit installed underground
Correct answer: A metal underground water pipe with at least 10 feet in direct contact with the earth
NEC 250.52(A)(1) permits a metal underground water pipe with at least 10 feet of direct earth contact as a grounding electrode.
Question 7: Per NEC 250.119, which of the following is an acceptable identification for an equipment grounding conductor?
- White insulation with a black stripe
- Green insulation, bare conductor, or green insulation with yellow stripes (Correct answer)
- Gray insulation only
- Orange insulation for high-leg identification
Correct answer: Green insulation, bare conductor, or green insulation with yellow stripes
NEC 250.119 permits EGCs to be identified by green insulation, bare copper, or green insulation with one or more yellow stripes.
NCCER Electrical Grounding & Bonding 1
What is the primary purpose of an equipment grounding conductor (EGC) in an electrical circuit?