Grounding and bonding is one of the most confusing parts of the code, and one of the most tested. You need to know which conductor does what and which table sizes it.
Every question here is based on the 2023 NEC. Some states are on a different edition, so check which one your exam uses.
-
Question 1 of 15
Which NEC term BEST matches: 'Connected to ground or to a conductive body that extends the ground connection'?
Show answerHide answer
Answer: A. Grounded
'Grounded' means connected to ground or to a conductive body that extends the ground connection (Article 100).
-
Question 2 of 15
Which statement BEST distinguishes a bonding jumper from a grounding electrode conductor (GEC)?
Show answerHide answer
Answer: A. A bonding jumper ensures continuity between metal parts; a GEC connects to the grounding electrode system (earth)
Bonding jumpers are used to bond metal parts together for continuity and fault path effectiveness, while a GEC connects the system/service to the grounding electrode system (earth).
-
Question 3 of 15
In a grounded utility service with one service disconnect, where is the neutral-to-ground bond made?
Show answerHide answer
Answer: A. The service disconnecting means (service equipment)
250.24(C) requires the main bonding jumper at the service disconnecting means. On the load side, 250.24(B) prohibits connecting the grounded conductor to equipment grounding conductors or metal parts, so downstream panels keep neutrals isolated.
-
Question 4 of 15
A building has two qualifying ground rods installed as grounding electrodes. The NEC generally requires that they be:
Show answerHide answer
Answer: A. Bonded together to form the grounding electrode system
All grounding electrodes present at a building must be bonded together to form the grounding electrode system per NEC 250.50.
-
Question 5 of 15
A technician says: 'If the breaker trips during a ground fault, that proves the ground rod did its job.' The MOST accurate response is:
Show answerHide answer
Answer: A. A breaker trip shows fault current found a low-impedance path back to the source; it doesn't show the ground rod was effective
A breaker trips when enough fault current flows, which requires an effective ground-fault current path back to the source (250.4(A)(5)). The trip doesn't show which path the current took, and the earth is not an effective ground-fault current path, so it doesn't prove the rod did anything.
-
Question 6 of 15
A branch circuit is protected by a 15-amp breaker. A wire-type copper EGC is used, and no upsizing applies. What is the minimum EGC size from Table 250.122?
Show answerHide answer
Answer: A. 14 AWG
Per NEC Table 250.122, a 15A overcurrent device requires a minimum 14 AWG copper equipment grounding conductor.
-
Question 7 of 15
In a subpanel, the grounded (neutral) conductors should terminate on:
Show answerHide answer
Answer: A. An insulated neutral bar isolated from the panel enclosure
Neutrals in a subpanel terminate on an insulated bar isolated from the enclosure to prevent normal return current from flowing on metal parts/grounding paths.
-
Question 8 of 15
Which NEC section provides the sizing requirements for grounding electrode conductors (GECs)?
Show answerHide answer
Answer: A. 250.66
NEC 250.66 sizes the grounding electrode conductor of an AC system using Table 250.66, based on the largest ungrounded service-entrance conductor (or equivalent area for parallel conductors). 250.66(A) through (C) allow smaller conductors where the GEC is the sole connection to certain electrode types.
-
Question 9 of 15
A very common exam trap is: 'Earth (ground rods) clears ground faults.' The BEST NEC-based correction is:
Show answerHide answer
Answer: A. Faults are cleared by an effective ground-fault current path back to the source; the earth is not an effective ground-fault current path
250.4(A)(5) requires an effective ground-fault current path back to the source so the OCPD opens, and states that the earth shall not be considered an effective ground-fault current path. Earth's impedance is too high to let enough fault current flow.
-
Question 10 of 15
Which NEC section provides the sizing requirements for equipment grounding conductors (EGCs)?
Show answerHide answer
Answer: A. 250.122
NEC 250.122 provides the minimum size requirements for equipment grounding conductors based on the rating of the overcurrent device.
-
Question 11 of 15
The MAIN reason neutrals and equipment grounds must generally be separated in subpanels is to prevent:
Show answerHide answer
Answer: A. Objectionable current on metal parts and equipment grounding paths
If neutrals and grounds are bonded in a subpanel, normal neutral return current can flow on equipment grounding paths and metal parts, creating objectionable current and shock hazards.
-
Question 12 of 15
If structural building steel qualifies as a grounding electrode, NEC generally requires that it be:
Show answerHide answer
Answer: A. Bonded into the grounding electrode system
Structural steel that qualifies as a grounding electrode must be bonded into the grounding electrode system per NEC 250.50 and 250.52.
-
Question 13 of 15
A ground fault occurs in a metal conduit run. The current travels through the conduit and a bonding bushing to the service, then through the main bonding jumper onto the grounded service conductor back to the utility source. What is this path?
Show answerHide answer
Answer: A. The effective ground-fault current path
The effective ground-fault current path is an intentionally constructed, low-impedance path that carries fault current back to the source so the OCPD can open. At the service, the main bonding jumper connects it to the grounded service conductor, which returns the current to the source.
-
Question 14 of 15
Which NEC section MOST directly addresses how equipment grounding conductors must be connected and spliced in boxes?
Show answerHide answer
Answer: A. 250.148
NEC 250.148 covers the continuity and connection of equipment grounding conductors and bonding of boxes/devices where EGCs are spliced or terminated.
-
Question 15 of 15
A technician measures current on the EGC in a subpanel under normal load with no fault. Which condition could explain the reading?
Show answerHide answer
Answer: A. A neutral-to-ground connection downstream of the service, such as a bonding screw left in a subpanel
A downstream neutral-to-ground connection creates a parallel path, so some normal neutral current returns on the EGC (250.6, 250.24(B)). The reading alone doesn't prove it, since equipment leakage can also put small currents on an EGC; you confirm by finding the neutral-to-case connection.
Want more? Electrician Practice has 1,100+ practice questions with explanations.
The classic mix-up: Table 250.66 sizes the grounding electrode conductor, and Table 250.122 sizes the equipment grounding conductor.
If subpanel questions tripped you up, remember the neutral and ground stay separate after the service.
Want more questions like these?
Electrician Practice has 1,100+ practice questions with explanations, timed practice exams, and weak-area drills.