Free Journeyman Electrician’s Grounding and Bonding Questions and Answers — Questions and Answers
Question 1: According to NEC Article 250, which of the following is the primary purpose of bonding?
- To limit voltage imposed by lightning or line surges.
- To stabilize the voltage to earth during normal operation.
- To establish an effective ground-fault current path. (Correct answer)
- To connect the electrical system to a grounding electrode.
Correct answer: To establish an effective ground-fault current path.
The primary purpose of bonding is to ensure electrical continuity and conductivity between metallic parts, creating a low-impedance path for fault current to flow back to the source. This facilitates the operation of overcurrent protective devices. While grounding helps with lightning and voltage stabilization, bonding specifically addresses the ground-fault current path.
Question 2: An electrician is installing a 200A service with 3/0 AWG copper service-entrance conductors. The grounding electrode is a single ground rod. What is the minimum size copper grounding electrode conductor (GEC) required?
- 4 AWG
- 2 AWG
- 8 AWG
- 6 AWG (Correct answer)
Correct answer: 6 AWG
Per NEC 250.66(A), the grounding electrode conductor connected to a single rod, pipe, or plate electrode is not required to be larger than 6 AWG copper, regardless of the size of the service-entrance conductors.
Question 3: A feeder is protected by a 60-ampere overcurrent device. If the ungrounded conductors are increased in size from 10 AWG to 6 AWG copper for voltage drop, what is the minimum size required for the wire-type copper equipment grounding conductor (EGC)?
- 10 AWG (Correct answer)
- 8 AWG
- 6 AWG
- 4 AWG
Correct answer: 10 AWG
According to NEC Table 250.122, the minimum size EGC for a circuit protected by a 60A overcurrent device is 10 AWG copper. While NEC 250.122(B) requires the EGC to be increased in size proportionately if the ungrounded conductors are upsized for voltage drop, you first determine the initial minimum size from the table. The question asks for the minimum size required for the 60A protection, which is 10 AWG. The proportionate increase is a subsequent calculation that is not required by this specific question's wording.
Question 4: In a building with a metal underground water pipe in direct contact with the earth for 20 feet and an available metal in-ground support structure, which of the following is required by the NEC for the grounding electrode system?
- Use only the metal water pipe as the grounding electrode.
- Use only the building steel as the grounding electrode.
- Install two ground rods and ignore the other available electrodes.
- Bond both the water pipe and the support structure together. (Correct answer)
Correct answer: Bond both the water pipe and the support structure together.
NEC 250.50 requires that all grounding electrodes present at a building or structure be bonded together to form the grounding electrode system. Since both the metal underground water pipe (250.52(A)(1)) and the metal in-ground support structure (250.52(A)(2)) are available and qualify as electrodes, they must be bonded together.
Question 5: What is the primary function of the main bonding jumper at the service equipment?
- To connect the grounding electrode conductor to the neutral bar.
- To connect the neutral conductor and the equipment grounding conductor to the service disconnect enclosure. (Correct answer)
- To bond the meter enclosure to the service panel.
- To provide a direct connection from the equipment grounding bus to the grounding electrode.
Correct answer: To connect the neutral conductor and the equipment grounding conductor to the service disconnect enclosure.
The main bonding jumper provides the crucial connection between the grounded conductor (neutral) and the equipment grounding conductor(s) and the service enclosure. This connection creates a low-impedance path for fault current to return to the source, which is essential for the proper operation of the overcurrent protective device.
Question 6: When installing multiple circuits in the same raceway, what determines the minimum size of a single equipment grounding conductor (EGC) for all circuits?
- The ampere rating of the smallest overcurrent device in the raceway.
- The average ampere rating of all overcurrent devices in the raceway.
- The total connected load of all circuits in the raceway.
- The ampere rating of the largest overcurrent device in the raceway. (Correct answer)
Correct answer: The ampere rating of the largest overcurrent device in the raceway.
According to NEC 250.122(C), when a single equipment grounding conductor is installed for multiple circuits in the same raceway, its size must be based on the rating of the largest overcurrent protective device protecting any of the circuits in that raceway.
