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NEC CODE NEC 2020

Overcurrent Protection Practice Test 2 (NEC 240) — NEC 2020 Edition

Free NEC 2020 practice test on overcurrent protection. Covers conductor protection limits, standard fuse/breaker sizing, next-size-up rounding, branch-circuit device location, multiwire circuits, and special equipment protection (welders, transformers). 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 Overcurrent Protection Practice Test 2 (NEC 240) — 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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Overcurrent Protection Practice Test 2 (NEC 240) — NEC 2020 Edition — Question List

Question 1: What is the maximum standard overcurrent device size generally allowed to protect a 12 AWG copper conductor?

20 amperes
15 amperes
25 amperes
30 amperes

NEC Reference: NEC 240.4(D)(5)

Question 2: On a residential electric service, which conductors generally require overcurrent protection?

Ungrounded conductors
Grounded conductors
Neutral conductors
Equipment grounding conductors

NEC Reference: NEC 240.21

Question 3: Three single-phase motors, with full-load currents of 20, 25, and 30 amperes, are connected to a 240-volt circuit. What dual-element fuse size can be used for the group?

110 amperes
150 amperes
200 amperes
175 amperes

NEC Reference: NEC Table 430.52

Question 4: When a fuse or circuit breaker is used as an overcurrent protective device, how must it be connected in the circuit?

In series
In parallel
Both series and parallel
It does not matter

NEC Reference: NEC Article 240

Question 5: Where must the branch-circuit overcurrent protective device generally be located in relation to the branch circuit it protects?

At the panelboard where it receives power
At the equipment ground location
At the end of the branch circuit
At the power outlet where power is consumed

NEC Reference: NEC 240.21

Question 6: A multiwire branch circuit that is protected by fuses may supply only what type of loads?

Line-to-neutral loads
Line-to-line loads
Receptacle loads only
Service loads

NEC Reference: NEC 210.4(C)

Question 7: For a resistance welder, the maximum overcurrent device rating is generally what percent of the welder's rated primary current?

Not over 300%
Not over 100%
Not over 200%
Not over 400%

NEC Reference: NEC 630.12

Question 8: What is the maximum overcurrent device rating required for an autotransformer with a full-load input current of 50 amperes?

75 amperes
50 amperes
80 amperes
65 amperes

NEC Reference: NEC 450.4(A)

Question 9: A busway or conductor has an allowable ampacity of 48 amperes, which is not a standard overcurrent device rating. What is the maximum standard overcurrent device rating that may protect it?

50 amperes
40 amperes
60 amperes
70 amperes

NEC Reference: NEC 240.4(B)

Question 10: Per the NEC standard ampere ratings, what is generally the smallest standard fuse or breaker rating commonly used for a 120-volt residential branch circuit?

15 amperes
20 amperes
12 amperes
18 amperes

NEC Reference: NEC 240.6(A)

Question 11: What is the maximum standard overcurrent device size generally allowed to protect a 14 AWG copper conductor?

15 amperes
20 amperes
25 amperes
30 amperes

NEC Reference: NEC 240.4(D)(3)

Question 12: What is the maximum standard overcurrent device size generally allowed to protect a 10 AWG copper conductor?

30 amperes
25 amperes
35 amperes
40 amperes

NEC Reference: NEC 240.4(D)(7)

Question 13: Which of the following is a standard ampere rating listed in NEC 240.6(A)?

40 amperes
37 amperes
42 amperes
33 amperes

NEC Reference: NEC 240.6(A)

Question 14: Supplementary overcurrent protective devices, as described in NEC 240.10, are used to protect what?

Individual pieces of equipment
The entire building service
Nothing at all
Utility company transformers

NEC Reference: NEC 240.10

Question 15: Per NEC 240.24(A), the center of the grip of a circuit breaker handle, in its highest position, must generally not be higher than what height above the floor?

6 feet 7 inches
5 feet
8 feet
10 feet

NEC Reference: NEC 240.24(A)

Question 16: Overcurrent devices must generally not be located in which of the following rooms?

Bathrooms
Garages
Basements
Kitchens

NEC Reference: NEC 240.24(E)

Question 17: Under the 10-foot tap rule, a feeder tap conductor not over 10 feet long generally must have an ampacity of not less than what?

The load served, and the terminating device rating
Any size at all
Half the feeder conductor size
A fixed 15 amperes always

NEC Reference: NEC 240.21(B)(1)

Question 18: Under the 25-foot tap rule, feeder tap conductors must have an ampacity of not less than what fraction of the ampacity of the feeder overcurrent device?

One-third
One-half
Two-thirds
The full ampacity

NEC Reference: NEC 240.21(B)(2)

Question 19: Series-rated overcurrent device combinations must be selected and marked according to what requirement?

Their listing and field marking
The installer's preference
No rule applies
The panel color

NEC Reference: NEC 240.86

Question 20: A Type S fuse and its adapter are designed to be what, once installed?

Non-removable and non-interchangeable
Removable and interchangeable with any fuse
Not evaluated for safety at all
Made only of glass

NEC Reference: NEC 240.54(B)

Question 21: A cartridge fuse must have a voltage rating that is what, compared to the circuit voltage?

Not less than the circuit voltage
Always exactly equal
Lower than the circuit voltage
Voltage rating does not matter

NEC Reference: NEC 240.60(A)

Question 22: A circuit breaker used regularly to switch a circuit on and off must be marked how?

"SWD" or "HID" as applicable
No special marking is required
Only a red sticker
The manufacturer's logo only

NEC Reference: NEC 240.83(D)

Question 23: An overcurrent device's interrupting rating must be sufficient for what?

The available fault current at that point
The device's physical size
The room temperature
Nothing -- interrupting rating is not regulated

NEC Reference: NEC 110.9

Question 24: A lighting and appliance branch-circuit panelboard must generally be protected by an overcurrent device rated no more than what, relative to the panelboard?

Not more than the panelboard rating
150% of the panelboard rating
Any rating at all
Half the panelboard rating

NEC Reference: NEC 408.36

Question 25: Transformer secondary conductors installed under the 25-foot tap rule for transformers must be protected from physical damage and generally must terminate in what?

A single overcurrent device
No overcurrent device at all
Two separate services
A grounding rod only

NEC Reference: NEC 240.21(C)(6)

Question 26: Conductors with a 90 C insulation rating may use the 90 C ampacity column of NEC Table 310.16 for what specific purpose, even if terminations are only rated for 60 C or 75 C?

Applying ampacity adjustment/correction factors
Ignoring termination ratings completely
Nothing -- it is never permitted
Doubling the conductor's final rating

NEC Reference: NEC 110.14(C)

Question 27: Feeder conductors must generally be protected against overcurrent in accordance with their what?

Ampacity
Color
Length only
Manufacturer preference

NEC Reference: NEC 215.3

Question 28: Can an overcurrent device ever be permitted to open the grounded (neutral) conductor of a circuit?

Only if it opens all conductors together
Yes, always freely
Never under any condition
Only on weekends

NEC Reference: NEC 240.22

Question 29: Does the "next size up" rounding rule of NEC 240.4(B) apply to sizing overcurrent protection for transformer secondary conductors under 240.21(C)?

True -- it does not apply there
False -- it always applies everywhere
Only for three-phase transformers
Only for autotransformers

NEC Reference: NEC 240.4(B) / 240.21(C)

Question 30: Which of the following is a standard ampere rating listed in NEC 240.6(A), commonly used for larger residential feeders?

60 amperes
55 amperes
65 amperes
58 amperes

NEC Reference: NEC 240.6(A)

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.

Overcurrent Protection Practice Test 2 (NEC 240) — NEC 2020 Edition

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Key NEC References for This Test

Overcurrent Protection Practice Test 2 (NEC 240) — NEC 2020 Edition

How this test works

Frequently Asked Questions

Is this Overcurrent Protection Practice Test 2 (NEC 240) — NEC 2020 Edition free?

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What articles are covered on electrician licensing exams?

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Overcurrent Protection Practice Test 2 (NEC 240) — NEC 2020 Edition — Question List

Question 1: What is the maximum standard overcurrent device size generally allowed to protect a 12 AWG copper conductor?

Question 2: On a residential electric service, which conductors generally require overcurrent protection?

Question 3: Three single-phase motors, with full-load currents of 20, 25, and 30 amperes, are connected to a 240-volt circuit. What dual-element fuse size can be used for the group?

Question 4: When a fuse or circuit breaker is used as an overcurrent protective device, how must it be connected in the circuit?

Question 5: Where must the branch-circuit overcurrent protective device generally be located in relation to the branch circuit it protects?

Question 6: A multiwire branch circuit that is protected by fuses may supply only what type of loads?

Question 7: For a resistance welder, the maximum overcurrent device rating is generally what percent of the welder's rated primary current?

Question 8: What is the maximum overcurrent device rating required for an autotransformer with a full-load input current of 50 amperes?

Question 9: A busway or conductor has an allowable ampacity of 48 amperes, which is not a standard overcurrent device rating. What is the maximum standard overcurrent device rating that may protect it?

Question 10: Per the NEC standard ampere ratings, what is generally the smallest standard fuse or breaker rating commonly used for a 120-volt residential branch circuit?

Question 11: What is the maximum standard overcurrent device size generally allowed to protect a 14 AWG copper conductor?

Question 12: What is the maximum standard overcurrent device size generally allowed to protect a 10 AWG copper conductor?

Question 13: Which of the following is a standard ampere rating listed in NEC 240.6(A)?

Question 14: Supplementary overcurrent protective devices, as described in NEC 240.10, are used to protect what?

Question 15: Per NEC 240.24(A), the center of the grip of a circuit breaker handle, in its highest position, must generally not be higher than what height above the floor?

Question 16: Overcurrent devices must generally not be located in which of the following rooms?

Question 17: Under the 10-foot tap rule, a feeder tap conductor not over 10 feet long generally must have an ampacity of not less than what?

Question 18: Under the 25-foot tap rule, feeder tap conductors must have an ampacity of not less than what fraction of the ampacity of the feeder overcurrent device?

Question 19: Series-rated overcurrent device combinations must be selected and marked according to what requirement?

Question 20: A Type S fuse and its adapter are designed to be what, once installed?

Question 21: A cartridge fuse must have a voltage rating that is what, compared to the circuit voltage?

Question 22: A circuit breaker used regularly to switch a circuit on and off must be marked how?

Question 23: An overcurrent device's interrupting rating must be sufficient for what?

Question 24: A lighting and appliance branch-circuit panelboard must generally be protected by an overcurrent device rated no more than what, relative to the panelboard?

Question 25: Transformer secondary conductors installed under the 25-foot tap rule for transformers must be protected from physical damage and generally must terminate in what?

Question 26: Conductors with a 90 C insulation rating may use the 90 C ampacity column of NEC Table 310.16 for what specific purpose, even if terminations are only rated for 60 C or 75 C?

Question 27: Feeder conductors must generally be protected against overcurrent in accordance with their what?

Question 28: Can an overcurrent device ever be permitted to open the grounded (neutral) conductor of a circuit?

Question 29: Does the "next size up" rounding rule of NEC 240.4(B) apply to sizing overcurrent protection for transformer secondary conductors under 240.21(C)?

Question 30: Which of the following is a standard ampere rating listed in NEC 240.6(A), commonly used for larger residential feeders?

Key NEC References for This Test

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