Free E2 Grounding and Bonding Questions and Answers 1 — Questions and Answers
Question 1: What is the minimum size copper grounding electrode conductor (GEC) required for a service with 500 kcmil copper ungrounded service-entrance conductors?
- 2 AWG
- 1 AWG
- 1/0 AWG (Correct answer)
- 2/0 AWG
Correct answer: 1/0 AWG
NEC Table 250.66 is used to size the grounding electrode conductor based on the size of the service-entrance conductors. For 500 kcmil copper conductors, the table requires a minimum GEC size of 1/0 AWG copper. This ensures the GEC can safely conduct fault current to the grounding electrode.
Question 2: A grounding electrode conductor is connected only to a concrete-encased electrode (Ufer ground). What is the largest size copper conductor required for this connection?
- 6 AWG
- 4 AWG (Correct answer)
- 2 AWG
- 1/0 AWG
Correct answer: 4 AWG
According to NEC 250.66(B), if a grounding electrode conductor is connected solely to a concrete-encased electrode, it is not required to be larger than 4 AWG copper. This is because the concrete encasement provides protection and limits the potential fault current the conductor would need to carry.
Question 3: Which of the following, if present and meeting the required specifications, MUST be used as part of the grounding electrode system for a commercial building?
- An interior metal water pipe
- A metal underground gas piping system
- A metal underground water pipe (Correct answer)
- The aluminum siding of the building
Correct answer: A metal underground water pipe
NEC 250.52(A) lists the items that are required to be used as grounding electrodes if they are present. A metal underground water pipe in direct contact with the earth for 10 feet or more is listed in 250.52(A)(1) and must be part of the grounding electrode system. Interior piping and gas piping are specifically prohibited or restricted for use as electrodes.
Question 4: What is the minimum size copper equipment grounding conductor (EGC) required for a branch circuit protected by a 400-ampere circuit breaker?
- 4 AWG
- 3 AWG (Correct answer)
- 2 AWG
- 1 AWG
Correct answer: 3 AWG
NEC Table 250.122 sizes the equipment grounding conductor based on the rating of the overcurrent protective device. For a 400-ampere OCPD, the table specifies a minimum EGC size of 3 AWG copper. The EGC provides a low-impedance path for fault current to facilitate the opening of the OCPD.
Question 5: On the load side of the service disconnect, which conductor is generally prohibited from being used to ground the metal frame of equipment?
- The equipment grounding conductor
- A bonding jumper
- The grounding electrode conductor
- The grounded conductor (Correct answer)
Correct answer: The grounded conductor
NEC 250.142(B) prohibits using the grounded circuit conductor (neutral) for grounding non-current-carrying metal parts of equipment on the load side of the service disconnecting means. Doing so would allow normal neutral current to flow on equipment frames, creating a shock hazard. A separate equipment grounding conductor must be used.
Question 6: A commercial service is supplied by 3/0 AWG copper conductors. What is the minimum size copper bonding jumper required to bond the interior metal water piping system to the service equipment?
- 6 AWG
- 4 AWG (Correct answer)
- 2 AWG
- 3/0 AWG
Correct answer: 4 AWG
The size of the bonding jumper for the metal water piping system is determined by NEC Table 250.102(C)(1), based on the size of the service conductors. For 3/0 AWG copper service conductors, the table requires a minimum bonding jumper size of 4 AWG copper. This ensures the piping system is effectively bonded to the grounding system.
Free E2 Grounding and Bonding Questions and Answers 1
What is the minimum size copper grounding electrode conductor (GEC) required for a service with 500 kcmil copper ungrounded service-entrance conductors?