EETC Grounding Systems 2 — Questions and Answers
Question 1: What is the minimum burial depth for a ground ring conductor installed in soil under the NEC?
- 6 inches
- 12 inches
- 18 inches (Correct answer)
- 24 inches
Correct answer: 18 inches
NEC 250.52(A)(4) requires a ground ring to be buried at least 30 inches (762 mm) below the surface of the earth — but the conductor within that ring must be at least 2 AWG and buried no less than 2.5 feet; the 30-inch rule applies.
Question 2: Which NEC article primarily governs grounding and bonding requirements?
- Article 230
- Article 240
- Article 250 (Correct answer)
- Article 310
Correct answer: Article 250
NEC Article 250 covers all requirements for grounding and bonding of electrical systems and equipment.
Question 3: A separately derived system's grounding electrode conductor must be connected at which point?
- At the first overcurrent device
- At the source of the separately derived system (Correct answer)
- At the main service panel
- At any convenient grounding electrode
Correct answer: At the source of the separately derived system
Per NEC 250.30, the grounding electrode conductor for a separately derived system must connect at the source — such as the secondary of a transformer.
Question 4: What term describes the low-impedance path provided to facilitate the operation of overcurrent devices during a ground fault?
- Equipment grounding
- System grounding
- Effective ground-fault current path (Correct answer)
- Bonding jumper path
Correct answer: Effective ground-fault current path
An effective ground-fault current path is a permanent, low-impedance electrically conductive path that facilitates overcurrent device operation during a ground fault.
Question 5: When is a main bonding jumper required?
- At every subpanel
- At the service entrance to bond the neutral to the equipment ground (Correct answer)
- At each grounding electrode
- At transformer secondaries only
Correct answer: At the service entrance to bond the neutral to the equipment ground
The main bonding jumper connects the grounded conductor (neutral) to the equipment grounding conductor and service equipment enclosure at the service entrance.
Question 6: Which of the following is NOT an acceptable grounding electrode under NEC 250.52?
- Metal water pipe with 10 ft in soil
- Concrete-encased electrode (Ufer ground)
- Copper pipe used for gas supply (Correct answer)
- Ground ring of bare copper
Correct answer: Copper pipe used for gas supply
Gas supply piping must never be used as a grounding electrode because it creates a fire and explosion hazard.
Question 7: What minimum size copper conductor is required for a grounding electrode conductor when the service entrance conductors are 3/0 AWG copper?
- 6 AWG
- 4 AWG (Correct answer)
- 2 AWG
- 1/0 AWG
Correct answer: 4 AWG
Per NEC Table 250.66, service entrance conductors of 2/0–3/0 AWG require a 4 AWG copper grounding electrode conductor.
EETC Grounding Systems 2
What is the minimum burial depth for a ground ring conductor installed in soil under the NEC?