PC - Professional Electrical Contractor Grounding and Bonding Questions and Answers

Question 1

An electrical service is supplied by 3/0 AWG copper ungrounded conductors.
The grounding electrode system consists solely of two 8-foot ground rods spaced 10 feet apart.
According to NEC Article 250, what is the minimum size copper grounding electrode conductor (GEC) required for this installation?

Accepted Answer

6 AWG

Answer

4 AWG

Answer

2 AWG

Answer

1/0 AWG

Question 2

A 400A feeder circuit's ungrounded conductors are increased in size from 500 kcmil copper to 750 kcmil copper to account for voltage drop. Per NEC Table 250.122, the minimum size copper equipment grounding conductor (EGC) for a 400A circuit is 3 AWG. What is the minimum size copper EGC required for this modified circuit?

Accepted Answer

1/0 AWG

Answer

3 AWG

Answer

2 AWG

Answer

1 AWG

Question 3

Which of the following best describes the primary purpose of bonding in an electrical system?

Accepted Answer

To provide a low-impedance path for fault current to facilitate the operation of overcurrent devices.

Answer

To stabilize the system voltage to ground during normal operation.

Answer

To provide a direct connection to the earth for lightning protection.

Answer

To limit voltage surges from the utility.

Question 4

A contractor installs a single ground rod as the grounding electrode for a new 200A service. A resistance measurement to earth shows a value of 30 ohms. According to the NEC, what is the appropriate next step?

Accepted Answer

Install a second grounding electrode and bond it to the first.

Answer

The installation is compliant as only one electrode is required.

Answer

Drive the single rod deeper until it reaches 25 ohms or less.

Answer

Replace the ground rod with a concrete-encased electrode.

Question 5

In a commercial building, a metal underground water pipe is used as the primary grounding electrode. Which of the following statements is correct regarding this installation?

Accepted Answer

A supplemental grounding electrode is required.

Answer

The metal water pipe is sufficient and no other electrodes are needed.

Answer

The grounding electrode conductor must be bonded to the pipe within 10 feet of where it enters the building.

Answer

The water pipe must be in direct contact with the earth for at least 8 feet.

Question 6

What is the primary function of the Main Bonding Jumper (MBJ) in a service panel?

Accepted Answer

To bond the service neutral conductor and the equipment grounding conductor(s) to the service disconnect enclosure.

Answer

To connect the grounding electrode conductor to the panel enclosure.

Answer

To connect the equipment grounding conductors to the neutral bar.

Answer

To provide a terminal for connecting bonding jumpers from other systems like telephone and CATV.