NEC Grounding and Bonding 3 — Questions and Answers
Question 1: According to NEC 250.68, how must a grounding electrode conductor connection to a grounding electrode be made?
- Accessible and using listed means (Correct answer)
- Buried at least 12 inches below grade
- Connected only with compression connectors
- Welded using exothermic welding only
Correct answer: Accessible and using listed means
NEC 250.68 requires grounding electrode conductor connections to be accessible and made with listed connectors, clamps, or fittings.
Question 2: What is the minimum burial depth for a bare copper grounding electrode conductor run underground per NEC 250.64(B)?
- No burial depth requirement — it may run exposed if protected (Correct answer)
- 6 inches
- 12 inches
- 18 inches
Correct answer: No burial depth requirement — it may run exposed if protected
NEC 250.64(B) allows grounding electrode conductors to be exposed or in a raceway but does not mandate burial; physical protection is required where subject to damage.
Question 3: Per NEC 250.30, what is required at a separately derived system such as a transformer?
- A system bonding jumper and grounding electrode (Correct answer)
- Only a grounding electrode conductor
- Only a system bonding jumper
- An equipment grounding conductor only
Correct answer: A system bonding jumper and grounding electrode
NEC 250.30(A) requires both a system bonding jumper and a grounding electrode for a separately derived system.
Question 4: Which of the following is NOT an acceptable grounding electrode per NEC 250.52?
- A plastic water pipe (Correct answer)
- A metal in-ground support structure
- A concrete-encased electrode
- A ground ring
Correct answer: A plastic water pipe
Plastic water pipe is not conductive and cannot serve as a grounding electrode; NEC 250.52 lists only metal or conductive electrodes.
Question 5: What minimum diameter must a ground rod electrode be if made of stainless steel or listed material per NEC 250.52(A)(5)?
- 5/8 inch (Correct answer)
- 1/2 inch
- 3/4 inch
- 1 inch
Correct answer: 5/8 inch
NEC 250.52(A)(5) requires ground rods of stainless steel or listed materials to be at least 5/8 inch in diameter.
Question 6: Under NEC 250.104, what must be bonded in a building that has a metal gas piping system?
- The metal gas piping must be bonded to the equipment grounding conductor (Correct answer)
- Gas piping must be bonded to the water pipe only
- Gas piping requires no bonding if it enters through plastic fittings
- Gas piping must be bonded to the grounding electrode directly
Correct answer: The metal gas piping must be bonded to the equipment grounding conductor
NEC 250.104(B) requires metal gas piping to be bonded to the equipment grounding conductor of the circuit that may energize the piping.
Question 7: Per NEC 250.142, which systems are permitted to use the grounded conductor (neutral) to ground equipment on the supply side of the service?
- Service equipment and meter enclosures only (Correct answer)
- All panelboards in the building
- Subpanels fed from the main service
- Any equipment connected to the grounded conductor
Correct answer: Service equipment and meter enclosures only
NEC 250.142(A) permits using the grounded conductor to ground equipment only on the supply side of or within service equipment.
NEC Grounding and Bonding 3
According to NEC 250.68, how must a grounding electrode conductor connection to a grounding electrode be made?