FREE NEC Grounding and Bonding Questions and Answers

Question 1

An electrician is installing a new 480/277V, 3-phase separately derived system from a transformer inside a building. According to NEC 250.30(A), which of the following must be used as the grounding electrode for this new system?

Accepted Answer

The existing building or structure grounding electrode system

Answer

NEC Section 250.30(A)(4) mandates that the existing building or structure grounding electrode system shall be used as the grounding electrode for a separately derived system. This ensures all systems within a building are bonded to a common electrode system, preventing potential differences between them.

Question 2

When installing an equipotential bonding grid for a permanently installed swimming pool, what is the MINIMUM size solid copper conductor required by NEC Article 680?

Accepted Answer

8 AWG

Answer

According to NEC Section 680.26(B), the conductors used for equipotential bonding in and around swimming pools must be solid copper and not smaller than 8 AWG. Aluminum conductors are not permitted for this application due to corrosion concerns.

Question 3

A service is supplied by 500 kcmil copper ungrounded service-entrance conductors. If the only connection to the grounding electrode system is to two 8-foot ground rods, what is the MINIMUM size copper grounding electrode conductor (GEC) required?

Accepted Answer

6 AWG

Answer

NEC Section 250.66(A) provides an exception to the general sizing rules in Table 250.66. It states that if a grounding electrode conductor connects only to rod, pipe, or plate electrodes, the conductor is not required to be larger than 6 AWG copper.

Question 4

A main bonding jumper is being installed in a service panel. Its size is determined based on which of the following?

Accepted Answer

The size of the ungrounded service-entrance conductors

Answer

According to NEC 250.28(D) and Table 250.102(C)(1), the main bonding jumper shall be sized based on the size of the ungrounded service-entrance conductors. This ensures the jumper can safely carry any fault current it might be subjected to.

Question 5

Which of the following locations is a required point of attachment for bonding an interior metal water piping system in a building?

Accepted Answer

The service equipment enclosure

Answer

NEC Section 250.104(A)(1) requires the metal water piping system to be bonded to the service equipment enclosure, the grounded service conductor, the grounding electrode conductor, or one of the grounding electrodes used. The service equipment enclosure is one of the specifically listed and most common points of attachment.

NEC Practice Test

NEC Practice Test

FREE NEC Grounding and Bonding Questions and Answers