EETC Grounding Systems 3 — Questions and Answers
Question 1: What is the purpose of equipotential bonding in a swimming pool area?
- To increase current flow for safety
- To eliminate voltage differences between conductive parts that a person could contact (Correct answer)
- To reduce the size of the grounding electrode required
- To allow the pool pump to operate without a GFCI
Correct answer: To eliminate voltage differences between conductive parts that a person could contact
Equipotential bonding ties all metallic parts together so no dangerous voltage difference exists between surfaces a person can simultaneously touch.
Question 2: A concrete-encased electrode must contain at least how many feet of steel rebar or 4 AWG bare copper conductor?
- 10 feet
- 15 feet
- 20 feet (Correct answer)
- 25 feet
Correct answer: 20 feet
NEC 250.52(A)(3) requires at least 20 feet of one or more steel reinforcing bars or 20 feet of bare copper conductor encased in concrete.
Question 3: Which conductor connects the grounding electrode to the grounded conductor or equipment?
- Bonding jumper
- Equipment grounding conductor
- Grounding electrode conductor (Correct answer)
- System neutral
Correct answer: Grounding electrode conductor
The grounding electrode conductor (GEC) is the conductor that connects the grounding electrode system to the grounded conductor or to the equipment grounding conductor.
Question 4: In a high-impedance grounded neutral system, what is the primary advantage over a solidly grounded system?
- Lower installation cost
- Allows continued operation during a single line-to-ground fault without tripping (Correct answer)
- Eliminates the need for grounding electrodes
- Provides better protection against lightning
Correct answer: Allows continued operation during a single line-to-ground fault without tripping
High-impedance grounding limits ground fault current to a very low level, allowing the system to continue operating during a single ground fault while an alarm alerts personnel.
Question 5: What is the maximum resistance to ground permitted for a made electrode (ground rod) per NEC 250.56 when a single rod is used?
- 5 ohms
- 25 ohms (Correct answer)
- 50 ohms
- 100 ohms
Correct answer: 25 ohms
NEC 250.56 requires that if a single ground rod has a resistance to earth exceeding 25 ohms, an additional grounding electrode must be installed.
Question 6: Which type of grounding electrode is also known as a 'Ufer ground'?
- Ground rod
- Ground ring
- Concrete-encased electrode (Correct answer)
- Metal water pipe
Correct answer: Concrete-encased electrode
The concrete-encased electrode was pioneered by Herbert G. Ufer and is commonly called a 'Ufer ground'; it uses rebar or copper in concrete footings.
Question 7: When multiple grounding electrodes are used, they must be bonded together. What is this collection of electrodes called?
- Ground bus
- Electrode array
- Grounding electrode system (Correct answer)
- Common ground grid
Correct answer: Grounding electrode system
NEC 250.50 requires that all electrodes present at a building or structure be bonded together to form the grounding electrode system.
EETC Grounding Systems 3
What is the purpose of equipotential bonding in a swimming pool area?