Electrician Grounding and Bonding 2 — Questions and Answers
Question 1: For a separately derived system such as a step-down transformer, where must the system bonding jumper be installed per NEC 250.30(A)(1)?
- At the first overcurrent device downstream of the transformer
- At the transformer primary terminals
- At the source of the separately derived system (Correct answer)
- At the remote panelboard served by the transformer
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 to establish the neutral-to-ground bond.
Question 2: Per NEC 250.52(A)(3), a concrete-encased grounding electrode must contain at least how much bare copper conductor or rebar encased in the concrete?
- 10 feet
- 15 feet
- 20 feet (Correct answer)
- 25 feet
Correct answer: 20 feet
NEC 250.52(A)(3) requires at least 20 feet of bare copper conductor or rebar encased within a concrete foundation to qualify as a concrete-encased electrode.
Question 3: Per NEC 250.56, if a single ground rod electrode has a resistance to earth exceeding what value, a supplemental electrode must be added?
- 15 ohms
- 25 ohms (Correct answer)
- 50 ohms
- 100 ohms
Correct answer: 25 ohms
NEC 250.56 requires a supplemental grounding electrode whenever a single rod electrode has a measured resistance exceeding 25 ohms.
Question 4: Which NEC table is used to determine the minimum size of a grounding electrode conductor based on the size of the service entrance conductors?
- Table 250.52
- Table 250.66 (Correct answer)
- Table 310.16
- Table 250.122
Correct answer: Table 250.66
NEC Table 250.66 cross-references service entrance conductor size to the minimum required grounding electrode conductor size.
Question 5: What is the minimum conductor size required for a ground ring grounding electrode per NEC 250.52(A)(4)?
- 6 AWG bare copper
- 4 AWG bare copper
- 2 AWG bare copper (Correct answer)
- 1/0 AWG bare copper
Correct answer: 2 AWG bare copper
NEC 250.52(A)(4) requires a ground ring to consist of at least 2 AWG bare copper conductor encircling the building or structure.
Question 6: At what minimum depth below grade must a ground ring electrode be buried per NEC 250.52(A)(4)?
- 18 inches
- 24 inches
- 30 inches (Correct answer)
- 36 inches
Correct answer: 30 inches
NEC 250.52(A)(4) requires the ground ring conductor to be buried at least 30 inches (750 mm) below the earth's surface.
Question 7: Per NEC 250.53(B), what is the minimum separation required between two ground rod electrodes when more than one is installed?
- 2 feet
- 4 feet
- 6 feet (Correct answer)
- 8 feet
Correct answer: 6 feet
NEC 250.53(B) requires ground rods to be spaced at least 6 feet apart so each rod contacts independent soil and resistance zones do not overlap.
Electrician Grounding and Bonding 2
For a separately derived system such as a step-down transformer, where must the system bonding jumper be installed per NEC 250.30(A)(1)?