E2 Grounding and Bonding 3 — Questions and Answers
Question 1: Under NEC 250.104, metal water piping systems in a commercial building must be bonded to which of the following?
- Grounding electrode only
- Service equipment enclosure, grounded conductor, or grounding electrode conductor (Correct answer)
- Each electrical panel individually
- Building structural steel only
Correct answer: Service equipment enclosure, grounded conductor, or grounding electrode conductor
NEC 250.104(A) requires metal water piping systems to be bonded to the service equipment enclosure, grounded conductor, or grounding electrode conductor.
Question 2: What is the minimum burial depth for a ground rod electrode per NEC 250.53(G)?
- 4 feet
- 6 feet
- 8 feet (Correct answer)
- 10 feet
Correct answer: 8 feet
NEC 250.53(G) requires ground rods to be driven to a depth of at least 8 feet to ensure adequate earth contact.
Question 3: Which type of grounding electrode is considered a 'made electrode' under NEC 250.52(B)?
- Concrete-encased electrode
- Metal underground water pipe
- Ground rod (Correct answer)
- Building steel
Correct answer: Ground rod
Ground rods (and ground plates/rings) are classified as 'made electrodes' under NEC 250.52(B) because they are installed specifically for grounding.
Question 4: When is a main bonding jumper required in service equipment?
- Only for services over 400 amperes
- At every service disconnect enclosure (Correct answer)
- Only when the neutral is not grounded
- Only for three-phase services
Correct answer: At every service disconnect enclosure
NEC 250.28 requires a main bonding jumper at each service disconnecting means to bond the grounded conductor to the equipment grounding conductor and enclosure.
Question 5: Concrete-encased electrodes (Ufer grounds) must contain at least how many feet of rebar or wire?
- 10 feet
- 20 feet (Correct answer)
- 25 feet
- 50 feet
Correct answer: 20 feet
NEC 250.52(A)(3) requires at least 20 feet of one or more steel reinforcing bars or bare copper conductors encased in concrete.
Question 6: A supply-side bonding jumper is used in which location?
- On the load side of the service overcurrent device
- Between the service point and service disconnecting means (Correct answer)
- Within branch circuit panels only
- At every junction box
Correct answer: Between the service point and service disconnecting means
Supply-side bonding jumpers are installed between the service point and the service disconnecting means, on the line side of the overcurrent device.
Question 7: What determines the minimum size of the grounding electrode conductor for a service using 4/0 AWG copper conductors?
- Rating of the main overcurrent device
- Size of the service-entrance conductors per NEC Table 250.66 (Correct answer)
- Total connected load
- Number of electrodes in the grounding electrode system
Correct answer: Size of the service-entrance conductors per NEC Table 250.66
NEC Table 250.66 sizes the grounding electrode conductor based on the size of the largest service-entrance conductor or equivalent area.
E2 Grounding and Bonding 3
Under NEC 250.104, metal water piping systems in a commercial building must be bonded to which of the following?