309A Grounding and Bonding 1 — Questions and Answers
Question 1: What is the primary purpose of grounding an electrical system?
- To reduce electricity consumption
- To stabilize voltage to earth and provide a path for fault current to operate protective devices (Correct answer)
- To increase the speed of motors
- To improve power factor
Correct answer: To stabilize voltage to earth and provide a path for fault current to operate protective devices
System grounding stabilizes the voltage relative to earth under normal conditions and provides a low-impedance fault current path that enables overcurrent protective devices to clear ground faults quickly.
Question 2: What is the difference between grounding and bonding?
- They are the same thing
- Grounding connects to earth; bonding connects metallic parts together to maintain equipotential (Correct answer)
- Bonding connects to earth; grounding connects metallic parts together
- Grounding is for AC systems; bonding is for DC systems
Correct answer: Grounding connects to earth; bonding connects metallic parts together to maintain equipotential
Grounding establishes a connection to earth, while bonding connects all metallic parts together to ensure they remain at the same potential, preventing shock hazards from voltage differences.
Question 3: According to the CEC, what is the minimum size of a copper grounding electrode conductor for a 100 A service?
- No. 8 AWG
- No. 6 AWG (Correct answer)
- No. 4 AWG
- No. 2 AWG
Correct answer: No. 6 AWG
CEC Table 17 specifies a minimum No. 6 AWG copper grounding electrode conductor for services up to 100 A, ensuring adequate capacity to carry fault current to the grounding electrode.
Question 4: What is a grounding electrode?
- A circuit breaker that trips on ground faults
- A conducting object that establishes a direct connection to earth (Correct answer)
- A type of bonding bushing
- An insulated conductor in a raceway
Correct answer: A conducting object that establishes a direct connection to earth
A grounding electrode is a conductive body (such as a ground rod, metal water pipe, or concrete-encased electrode) that makes direct contact with the earth to establish the ground reference.
Question 5: What is the minimum length for a ground rod used as a grounding electrode according to the CEC?
- 1.5 m (5 ft)
- 2.4 m (8 ft)
- 3.0 m (10 ft) (Correct answer)
- 3.6 m (12 ft)
Correct answer: 3.0 m (10 ft)
CEC Rule 10-700 requires ground rods to have a minimum length of 3.0 m (10 ft) and be driven to their full length to ensure adequate contact with earth for a low-resistance ground connection.
Question 6: What is the maximum permitted ground resistance for a single ground rod according to the CEC?
- 5 Ω
- 10 Ω
- 15 Ω
- 25 Ω (Correct answer)
Correct answer: 25 Ω
CEC Rule 10-702 requires a maximum ground resistance of 25 Ω for a single grounding electrode. If this cannot be achieved, additional electrodes must be installed.
309A Grounding and Bonding 1
What is the primary purpose of grounding an electrical system?