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NEC CODE NEC 2020

Grounding and Bonding (NEC 250) — NEC 2020 Edition

Free NEC 2020 practice test on grounding and bonding. Covers grounding purpose, grounded conductor identification, grounding electrode conductor sizing, electrode types, and bonding requirements. Simple English, full explanations.

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The National Electrical Code (NFPA 70) is the benchmark standard for safe electrical installation in the US. It is updated every 3 years by the NFPA.

Study the edition adopted by your state. As of 2025, most states use the 2020 or 2023 NEC. These tests are written to the 2023 edition.

The most tested articles are 100 (Definitions), 200–250 (Wiring & Grounding), 300–314 (Wiring Methods), 400–411 (Conductors), 430 (Motors), and 700–701 (Emergency Systems).

How to Use This Practice Test

This Grounding and Bonding (NEC 250) — NEC 2020 Edition has 30 questions with detailed answers and NEC references. Take the full test, review every wrong answer, and look up the NEC article it references before moving on.

Tip: Use the NEC index (back of the book) — find answers by keyword, not by article number.

Topics covered: NEC articles 100, 210, 220, 240, 250, 300, 310, 430, and special occupancies.
Passing score: Aim for 80%+ on NEC code tests before exam day.
Questions: 30 multiple-choice, one correct answer each

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Grounding and Bonding (NEC 250) — NEC 2020 Edition — Question List

Question 1: What is the main purpose of grounding an electrical system, per NEC 250.4(A)(1)?

To limit voltage from lightning, surges, or unintentional contact
To increase system voltage
To eliminate all overcurrent devices
It has no real safety purpose

NEC Reference: NEC 250.4(A)(1)

Question 2: True or false: the secondary circuits of low-voltage lighting systems are generally not grounded.

True
False
Only for outdoor systems
Only for systems over 50 volts

NEC Reference: NEC 411.5

Question 3: True or false: an additional grounding connection must be made at a transformer supplying the service inside a building.

True
False
Only for 3-phase systems
Only for 3-wire systems

NEC Reference: NEC 250.24(A)(2)

Question 4: In a delta-connected, 3-phase, 3-wire system, the grounded conductor's ampacity must be less than the rating of what?

The ungrounded conductor
The secondary conductor
The neutral conductor
Nothing -- no limit applies

NEC Reference: NEC 250.24(C)(3)

Question 5: True or false: in a single raceway, the grounded conductor may be larger than the largest ungrounded conductor in the raceway.

True
False
Only in metal raceways
Only for services

NEC Reference: NEC 250.24(C)(1)

Question 6: In a single-phase, 3-wire electrical system, what is the middle conductor generally required to be?

Grounded
Ungrounded
A hot conductor
Not connected at all

NEC Reference: NEC 250.26

Question 7: Grounded (neutral) conductors 6 AWG and smaller are most commonly identified by which color?

White or natural gray
Red
Green
Black

NEC Reference: NEC 200.6(A)

Question 8: True or false: the grounded (neutral) conductor can never be interrupted by a circuit breaker or fuse under any circumstances.

True
False
Only for 3-phase systems
Only outdoors

NEC Reference: NEC 240.22

Question 9: A single-phase service uses 1/0 AWG aluminum as its largest ungrounded conductor. What size aluminum grounding electrode conductor is required?

Aluminum 6 AWG
Aluminum 4 AWG
Copper 2 AWG
Copper 6 AWG

NEC Reference: NEC Table 250.66

Question 10: Lightning protection system ground terminals must generally be bonded to which grounding system?

The building or structure grounding electrode system
A distribution panelboard only
The service entrance only
Nothing -- bonding is not required

NEC Reference: NEC 250.106

Question 11: An insulated equipment grounding conductor 6 AWG or smaller is usually identified by what color?

Green
Orange
Brown
Pink

NEC Reference: NEC 250.119

Question 12: A concrete-encased grounding electrode (Ufer ground) generally must have at least what length of qualifying conductor or rebar?

20 feet
10 feet
30 feet
50 feet

NEC Reference: NEC 250.52(A)(3)

Question 13: A ground rod must be driven so that how much of its length remains below grade?

The full rod length
Half of the rod
One inch
None -- it can stick straight up

NEC Reference: NEC 250.53(G)

Question 14: Where two ground rods are used, they should be spaced at least how far apart?

6 feet apart
1 foot apart
50 feet apart
Touching each other

NEC Reference: NEC 250.53(A)(3)

Question 15: Metal water piping in a building must be bonded to what?

The service equipment or grounding electrode system
Nothing at all
The nearest fence
A telephone pole

NEC Reference: NEC 250.104(A)

Question 16: A grounding electrode conductor may be made of what material?

Copper, aluminum, or copper-clad aluminum
Plastic only
Wood
Rubber

NEC Reference: NEC 250.62

Question 17: The main bonding jumper connects the equipment grounding conductor to the grounded conductor at what location?

At the service
At every subpanel equally
Nowhere -- it is optional
At the utility pole

NEC Reference: NEC 250.28

Question 18: A service uses 2 AWG copper as its largest ungrounded conductor. What size copper grounding electrode conductor is required?

8 AWG
10 AWG
6 AWG
4 AWG

NEC Reference: NEC Table 250.66

Question 19: A circuit is protected by a 60-ampere overcurrent device. What is the minimum size copper equipment grounding conductor required?

10 AWG
12 AWG
8 AWG
14 AWG

NEC Reference: NEC Table 250.122

Question 20: Grounding connections generally must be made using what type of fittings or methods?

Listed pressure connectors or clamps
Any random splice, no listing needed
Electrical tape only
Nothing is required

NEC Reference: NEC 250.8

Question 21: The bonding jumper size for the water piping system is based on what?

The largest ungrounded service conductor
The pipe color
The homeowner's preference
Nothing -- any size works

NEC Reference: NEC Table 250.66

Question 22: An isolated ground receptacle is generally used to reduce what, for sensitive electronic equipment?

Electrical noise
The room temperature
The building's square footage
Nothing useful

NEC Reference: NEC 250.146(D)

Question 23: An intersystem bonding termination is generally provided at the service to bond what type of systems to the building grounding electrode system?

Communications systems
Nothing -- it has no purpose
Only gas piping
Only HVAC ductwork

NEC Reference: NEC 250.94

Question 24: A metal underground water pipe in direct contact with earth for at least 10 feet is used as a grounding electrode. What additional requirement applies?

It must be supplemented by an additional electrode
No supplement is ever required
It must be removed instead
It must be painted

NEC Reference: NEC 250.53(D)(2)

Question 25: Metal piping systems (other than water piping) that may become energized, such as gas piping, generally must be what?

Bonded to the equipment grounding system
Left completely isolated
Removed entirely
Painted a bright color only

NEC Reference: NEC 250.104(B)

Question 26: A portable generator that only supplies equipment mounted on the generator, or cord-and-plug equipment through its own receptacles, may be exempt from what requirement?

A grounding electrode connection
Any grounding at all, permanently
A fuel cap
An oil change

NEC Reference: NEC 250.34

Question 27: A grounding electrode conductor exposed to physical damage must generally be what?

Protected, such as in a raceway
Left completely bare and exposed
Removed entirely
Painted red

NEC Reference: NEC 250.64(B)

Question 28: A separately derived system, such as the secondary of a step-down transformer, requires what type of bonding jumper at the source?

A system bonding jumper
No bonding jumper at all
A telephone wire
A padlock

NEC Reference: NEC 250.30(A)(1)

Question 29: Where multiple grounding electrodes are present at a building, what does NEC 250.50 require?

All present qualifying electrodes must be bonded together
Only one electrode may ever be used
They must be kept completely separate
Nothing -- bonding is optional

NEC Reference: NEC 250.50

Question 30: Which of the following can serve as an equipment grounding conductor, per NEC 250.118?

A copper conductor, or in some cases the metal raceway
A garden hose
A wooden dowel
Nothing is ever permitted

NEC Reference: NEC 250.118

Key NEC References for This Test

Article	What It Covers
Ch. 1–4	General rules — apply to all installations
Ch. 5–7	Special rules — override Ch. 1–4 where they conflict
Ch. 8	Communications — completely independent of Ch. 1–7
Ch. 9	Tables — referenced by articles, not standalone enforceable rules
Art. 210.12	AFCI — major expansion in NEC 2026
Art. 230.67	Surge protection at service equipment — new NEC 2026

Study Tip: Learn the NEC index — use keywords, not article numbers. Practice finding 5 different topics in under 2 minutes each.

Grounding and Bonding (NEC 250) — NEC 2020 Edition

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Key NEC References for This Test

Grounding and Bonding (NEC 250) — NEC 2020 Edition

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Frequently Asked Questions

Is this Grounding and Bonding (NEC 250) — NEC 2020 Edition free?

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Which NEC edition should I study?

What articles are covered on electrician licensing exams?

How to Use This Practice Test

Student Reviews

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Grounding and Bonding (NEC 250) — NEC 2020 Edition — Question List

Question 1: What is the main purpose of grounding an electrical system, per NEC 250.4(A)(1)?

Question 2: True or false: the secondary circuits of low-voltage lighting systems are generally not grounded.

Question 3: True or false: an additional grounding connection must be made at a transformer supplying the service inside a building.

Question 4: In a delta-connected, 3-phase, 3-wire system, the grounded conductor's ampacity must be less than the rating of what?

Question 5: True or false: in a single raceway, the grounded conductor may be larger than the largest ungrounded conductor in the raceway.

Question 6: In a single-phase, 3-wire electrical system, what is the middle conductor generally required to be?

Question 7: Grounded (neutral) conductors 6 AWG and smaller are most commonly identified by which color?

Question 8: True or false: the grounded (neutral) conductor can never be interrupted by a circuit breaker or fuse under any circumstances.

Question 9: A single-phase service uses 1/0 AWG aluminum as its largest ungrounded conductor. What size aluminum grounding electrode conductor is required?

Question 10: Lightning protection system ground terminals must generally be bonded to which grounding system?

Question 11: An insulated equipment grounding conductor 6 AWG or smaller is usually identified by what color?

Question 12: A concrete-encased grounding electrode (Ufer ground) generally must have at least what length of qualifying conductor or rebar?

Question 13: A ground rod must be driven so that how much of its length remains below grade?

Question 14: Where two ground rods are used, they should be spaced at least how far apart?

Question 15: Metal water piping in a building must be bonded to what?

Question 16: A grounding electrode conductor may be made of what material?

Question 17: The main bonding jumper connects the equipment grounding conductor to the grounded conductor at what location?

Question 18: A service uses 2 AWG copper as its largest ungrounded conductor. What size copper grounding electrode conductor is required?

Question 19: A circuit is protected by a 60-ampere overcurrent device. What is the minimum size copper equipment grounding conductor required?

Question 20: Grounding connections generally must be made using what type of fittings or methods?

Question 21: The bonding jumper size for the water piping system is based on what?

Question 22: An isolated ground receptacle is generally used to reduce what, for sensitive electronic equipment?

Question 23: An intersystem bonding termination is generally provided at the service to bond what type of systems to the building grounding electrode system?

Question 24: A metal underground water pipe in direct contact with earth for at least 10 feet is used as a grounding electrode. What additional requirement applies?

Question 25: Metal piping systems (other than water piping) that may become energized, such as gas piping, generally must be what?

Question 26: A portable generator that only supplies equipment mounted on the generator, or cord-and-plug equipment through its own receptacles, may be exempt from what requirement?

Question 27: A grounding electrode conductor exposed to physical damage must generally be what?

Question 28: A separately derived system, such as the secondary of a step-down transformer, requires what type of bonding jumper at the source?

Question 29: Where multiple grounding electrodes are present at a building, what does NEC 250.50 require?

Question 30: Which of the following can serve as an equipment grounding conductor, per NEC 250.118?

Key NEC References for This Test

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