Grounding and Bonding in Electrical
Systems UPDATED ACTUAL Exam
Questions and CORRECT Answers
What is the purpose of a Main Bonding Jumper (MBJ)? - CORRECT ANSWER - The MBJ
provides a path back to the source for faults that occur within the service disconnect means.
What must the MBJ be made of if it is a screw? - CORRECT ANSWER - It must have a
green finish so that the head of the screw is visible for inspection.
How should an MBJ be attached? - CORRECT ANSWER - Using exothermic welding, a
listed pressure connector, listed clamp, or other listed means.
What is the minimum size requirement for an MBJ according to NEC Table 250.102(C)(1)? -
CORRECT ANSWER - The MBJ cannot be smaller than the sizes given in NEC Table
250.102(C)(1).
What is the main function of a lightning rod? - CORRECT ANSWER - To dissipate the
negative static charge that would cause a positive lightning charge to strike a structure.
What does the NEC allow regarding ground faults in branch circuits and feeders? - CORRECT
ANSWER - It allows any ground fault to travel back to the source of supply at the utility.
What happens to the ground fault current without an MBJ? - CORRECT ANSWER - The path
back to the source would be through the grounding electrode system and the earth, which does
not provide a low-impedance path.
What is the formula to calculate current using Ohm's Law? - CORRECT ANSWER -I=E÷
R, where E is system voltage, R is resistance, and I is system current.
, In the example provided, what was the calculated current when using a resistance of 2002 ohms
and a voltage of 120V? - CORRECT ANSWER - The calculated current was 6A.
What is the smallest overcurrent device in the sample dwelling's electrical system? - CORRECT
ANSWER - 15A.
What does NEC Section 250.92(A) require regarding electrical continuity? - CORRECT
ANSWER - It requires that electrical continuity must be maintained at the service.
What items must be bonded according to NEC Section 250.92(A)? - CORRECT ANSWER -
Service raceways, auxiliary gutters, service cable armor or sheaths, service enclosures containing
service-entrance conductors, and any metallic raceway or armor enclosing a grounding electrode
conductor.
What is the significance of bonding intervening raceways, boxes, and enclosures? - CORRECT
ANSWER - Bonding ensures electrical continuity between the service equipment and the
grounding electrode.
What components typically require bonding in an electrical system? - CORRECT ANSWER -
The mast, weather-head, meter enclosure, armor of the SE cable (if it has armor), and the service
disconnect.
What is the exception noted in NEC Section 250.53(A)(2) regarding resistance? - CORRECT
ANSWER - The total resistance must be less than 250 ohms to ensure adequate current flow.
What is the role of the MBJ in relation to the grounded conductor of the service? - CORRECT
ANSWER - With the MBJ installed, the path back to the utility source is through the MBJ to
the grounded conductor, allowing sufficient current to flow.
What does the combined resistance of EMT and metal water piping affect? - CORRECT
ANSWER - It affects the amount of current that could flow back to the utility source.
Systems UPDATED ACTUAL Exam
Questions and CORRECT Answers
What is the purpose of a Main Bonding Jumper (MBJ)? - CORRECT ANSWER - The MBJ
provides a path back to the source for faults that occur within the service disconnect means.
What must the MBJ be made of if it is a screw? - CORRECT ANSWER - It must have a
green finish so that the head of the screw is visible for inspection.
How should an MBJ be attached? - CORRECT ANSWER - Using exothermic welding, a
listed pressure connector, listed clamp, or other listed means.
What is the minimum size requirement for an MBJ according to NEC Table 250.102(C)(1)? -
CORRECT ANSWER - The MBJ cannot be smaller than the sizes given in NEC Table
250.102(C)(1).
What is the main function of a lightning rod? - CORRECT ANSWER - To dissipate the
negative static charge that would cause a positive lightning charge to strike a structure.
What does the NEC allow regarding ground faults in branch circuits and feeders? - CORRECT
ANSWER - It allows any ground fault to travel back to the source of supply at the utility.
What happens to the ground fault current without an MBJ? - CORRECT ANSWER - The path
back to the source would be through the grounding electrode system and the earth, which does
not provide a low-impedance path.
What is the formula to calculate current using Ohm's Law? - CORRECT ANSWER -I=E÷
R, where E is system voltage, R is resistance, and I is system current.
, In the example provided, what was the calculated current when using a resistance of 2002 ohms
and a voltage of 120V? - CORRECT ANSWER - The calculated current was 6A.
What is the smallest overcurrent device in the sample dwelling's electrical system? - CORRECT
ANSWER - 15A.
What does NEC Section 250.92(A) require regarding electrical continuity? - CORRECT
ANSWER - It requires that electrical continuity must be maintained at the service.
What items must be bonded according to NEC Section 250.92(A)? - CORRECT ANSWER -
Service raceways, auxiliary gutters, service cable armor or sheaths, service enclosures containing
service-entrance conductors, and any metallic raceway or armor enclosing a grounding electrode
conductor.
What is the significance of bonding intervening raceways, boxes, and enclosures? - CORRECT
ANSWER - Bonding ensures electrical continuity between the service equipment and the
grounding electrode.
What components typically require bonding in an electrical system? - CORRECT ANSWER -
The mast, weather-head, meter enclosure, armor of the SE cable (if it has armor), and the service
disconnect.
What is the exception noted in NEC Section 250.53(A)(2) regarding resistance? - CORRECT
ANSWER - The total resistance must be less than 250 ohms to ensure adequate current flow.
What is the role of the MBJ in relation to the grounded conductor of the service? - CORRECT
ANSWER - With the MBJ installed, the path back to the utility source is through the MBJ to
the grounded conductor, allowing sufficient current to flow.
What does the combined resistance of EMT and metal water piping affect? - CORRECT
ANSWER - It affects the amount of current that could flow back to the utility source.
