CME Grounding, Bonding & Overcurrent Protection 1 — Questions and Answers
Question 1: What is the minimum size copper equipment grounding conductor (EGC) required for a circuit protected by a 100A overcurrent device per NEC Table 250.122?
- 8 AWG (Correct answer)
- 6 AWG
- 4 AWG
- 2 AWG
Correct answer: 8 AWG
NEC Table 250.122 specifies a minimum 8 AWG copper EGC for circuits protected by overcurrent devices rated up to 100A.
Question 2: Per NEC Article 250, what is the primary purpose of bonding metal parts in an electrical system?
- To increase the current-carrying capacity of conductors
- To establish electrical continuity and conductivity between metal parts (Correct answer)
- To reduce voltage drop in branch circuits
- To provide surge protection from lightning
Correct answer: To establish electrical continuity and conductivity between metal parts
Bonding establishes electrical continuity and conductivity between conductive parts to ensure a reliable fault current path and equalize potential differences.
Question 3: Which of the following is explicitly prohibited as a grounding electrode per NEC 250.52(B)?
- Concrete-encased electrode
- Metal underground gas piping system (Correct answer)
- Ground ring
- Metal water pipe with 10+ feet in soil
Correct answer: Metal underground gas piping system
NEC 250.52(B) explicitly prohibits metal underground gas piping systems from being used as grounding electrodes due to safety hazards.
Question 4: The main bonding jumper at a service connects which two components?
- The grounded (neutral) conductor to the equipment grounding conductor at the main service (Correct answer)
- The hot conductor to the neutral conductor at the panel
- The grounding electrode conductor to the service entrance conduit
- The neutral bar to the grounding electrode only
Correct answer: The grounded (neutral) conductor to the equipment grounding conductor at the main service
Per NEC 250.28, the main bonding jumper connects the grounded (neutral) conductor to the equipment grounding conductor and enclosure at the main service disconnect.
Question 5: Per NEC Table 250.66, what is the minimum size copper grounding electrode conductor (GEC) for a service with 3/0 AWG copper service-entrance conductors?
- 4 AWG (Correct answer)
- 2 AWG
- 1/0 AWG
- 2/0 AWG
Correct answer: 4 AWG
NEC Table 250.66 requires a 4 AWG copper GEC when the largest service-entrance conductor is 3/0 AWG copper.
Question 6: Per NEC 250.30, where must the system bonding jumper be installed for a separately derived system?
- At the first disconnecting means only
- At the source of the separately derived system (Correct answer)
- At both the source and at each distribution panel
- At the main service disconnect of the building
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 connect the grounded conductor to the equipment grounding conductor.
Question 7: Per NEC 110.9, equipment used to interrupt fault current must have an interrupting rating that is:
- At least equal to the maximum available fault current at its terminals (Correct answer)
- Rated for 10,000 AIC minimum regardless of system fault levels
- Determined only by the utility company
- Based solely on the conductor ampacity
Correct answer: At least equal to the maximum available fault current at its terminals
NEC 110.9 requires that equipment intended to interrupt current at fault levels must have an interrupting rating sufficient for the available fault current at its terminals.
CME Grounding, Bonding & Overcurrent Protection 1
What is the minimum size copper equipment grounding conductor (EGC) required for a circuit protected by a 100A overcurrent device per NEC Table 250.122?