309A Grounding and Bonding 2 — Questions and Answers
Question 1: What is the purpose of the bonding jumper at a service panel?
- To connect the neutral bus to the equipment grounding bus (Correct answer)
- To connect the panel to the water pipe only
- To provide overcurrent protection
- To isolate the neutral from ground
Correct answer: To connect the neutral bus to the equipment grounding bus
The main bonding jumper connects the neutral bus to the equipment grounding bus at the service entrance panel, establishing the connection between the grounded conductor and the equipment grounding system.
Question 2: Why must the neutral and ground be bonded at only one point in a distribution system?
- To save on materials
- To prevent objectionable current flow on equipment grounding conductors (Correct answer)
- To increase system capacity
- To comply with utility requirements only
Correct answer: To prevent objectionable current flow on equipment grounding conductors
If neutral and ground are bonded at multiple points, normal return current can flow through equipment grounding conductors, metal raceways, and building steel, creating shock hazards and fire risks.
Question 3: What is the purpose of an equipment bonding conductor in a raceway system?
- To carry normal load current
- To provide a low-impedance path for fault current back to the source (Correct answer)
- To act as the neutral conductor
- To provide lightning protection
Correct answer: To provide a low-impedance path for fault current back to the source
The equipment bonding conductor provides a low-impedance fault current path from any point of a ground fault back to the source, enabling the overcurrent device to operate quickly and clear the fault.
Question 4: According to the CEC, what is the minimum bonding conductor size for a circuit protected by a 60 A breaker?
- No. 14 AWG
- No. 12 AWG
- No. 10 AWG (Correct answer)
- No. 8 AWG
Correct answer: No. 10 AWG
CEC Table 16 specifies the minimum bonding conductor size based on the overcurrent device rating. For a 60 A circuit, a No. 10 AWG copper bonding conductor is required.
Question 5: What is an intersystem bonding termination?
- A connector for bonding plumbing to electrical systems
- A device providing connection points for bonding communication system grounds to the power system ground (Correct answer)
- A type of ground rod connector
- A lightning arrestor mounting point
Correct answer: A device providing connection points for bonding communication system grounds to the power system ground
An intersystem bonding termination provides accessible connection points near the service entrance for bonding communication systems (telephone, cable TV, satellite) to the power system's grounding electrode system.
Question 6: What material must not be used as a sole grounding electrode?
- Copper rod
- Cast iron water pipe
- Concrete-encased rebar
- Aluminium rod driven into the earth (Correct answer)
Correct answer: Aluminium rod driven into the earth
Aluminium is not permitted as a grounding electrode in contact with earth because it corrodes rapidly in soil, losing its electrical connection to earth over time.
309A Grounding and Bonding 2
What is the purpose of the bonding jumper at a service panel?