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Overcurrent Protection Practice Test 1 (NEC 240) — NEC 2020 Edition

Free online NEC Article 240 overcurrent protection practice test. Covers conductor ampacity limits (14/12/10 AWG), standard OCPD ratings, the 10-foot and 25-foot tap rules, plug and cartridge fuse requirements, circuit breaker installation rules, and supplementary overcurrent protection. NEC 2020 edition — ideal for journeyman and master electrician exam preparation.

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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).

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This Overcurrent Protection Practice Test 1 (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 1 (NEC 240) — NEC 2020 Edition — Question List

Question 1: Under the 10-foot feeder tap rule, the tap conductors must have an ampacity not less than what?

The feeder conductor ampacity
The calculated load and the rating of the device they terminate in
125% of the feeder overcurrent device rating
One-third of the feeder overcurrent device rating

NEC Reference: NEC 240.21(B)(1)

Question 2: Tap conductors that leave an enclosure or vault must generally have an ampacity of not less than what fraction of the overcurrent device rating protecting the feeder conductors?

1/5
1/10
1/12
1/8

NEC Reference: NEC 240.21(B)(1)(4)

Question 3: A branch-circuit-rated circuit breaker marked for use with 18 AWG copper supplies a continuous load of 5.6 A. What overcurrent protection rating may be used?

7 amperes
10 amperes
15 amperes
20 amperes

NEC Reference: NEC 240.4(D)(1)

Question 4: How must an overcurrent device be connected to the ungrounded conductor it protects?

In series with the conductor
In parallel with the conductor
In the grounded conductor only
Across the conductor and ground

NEC Reference: NEC 240.15(A)

Question 5: In which location are overcurrent devices NOT permitted in dwelling units?

Basements
Bathrooms
Garages
Laundry rooms

NEC Reference: NEC 240.24(E)

Question 6: What is the maximum voltage between conductors for which plug fuses may generally be used as overcurrent protection?

150 volts
120 volts
240 volts
480 volts

NEC Reference: NEC 240.50(A)

Question 7: Which of these is NOT a standard ampere rating for fuses and inverse-time circuit breakers in 240.6(A)?

25 A
35 A
45 A
55 A

NEC Reference: NEC 240.6(A)

Question 8: A circuit changes from a larger conductor to a smaller conductor with no overcurrent device at the change. The overcurrent device must protect which conductor?

The smallest conductor
The largest conductor
Only the conductor at the panel
The average of the two

NEC Reference: NEC 240.4

Question 9: Under the 25-foot feeder tap rule, how must the tap conductors be protected from physical damage?

Only by a sign at the tap point
They need no protection if they are 25 ft or less
By an approved raceway or other approved means
By a fuse at each end

NEC Reference: NEC 240.21(B)(2)

Question 10: Per NEC 240.4(D), what is the maximum overcurrent protection permitted for 14 AWG copper conductors in a branch circuit?

10 A
15 A
20 A
25 A

NEC Reference: NEC 240.4(D)(3)

Question 11: Per NEC 240.4(D), what is the maximum overcurrent protection permitted for 12 AWG copper conductors?

15 A
20 A
25 A
30 A

NEC Reference: NEC 240.4(D)(5)

Question 12: Conductors are protected by a 1,200 A overcurrent device. What is their minimum ampacity?

1,000 A
1,100 A
1,200 A
960 A

NEC Reference: NEC 240.4(C)

Question 13: A 25-foot tap conductor runs from a feeder to a subpanel. Per NEC 240.21(B)(2), the tap conductors must terminate in a single circuit breaker or set of fuses rated at no more than what?

The rating of the upstream feeder OCPD
The ampacity of the tap conductors
125% of the continuous load
1/3 of the feeder OCPD rating

NEC Reference: NEC 240.21(B)(2)(3)

Question 14: Per NEC 240.21(B)(2), for the 25-foot tap rule to apply, the tap conductor ampacity must be not less than what fraction of the upstream feeder overcurrent device rating?

1/10
1/4
1/3
1/2

NEC Reference: NEC 240.21(B)(2)(1)

Question 15: Per NEC 240.6(A), which of the following is NOT a standard ampere rating for fuses and fixed-trip circuit breakers?

60 A
65 A
70 A
80 A

NEC Reference: NEC 240.6(A)

Question 16: Per NEC 240.24(A), the center of the grip of a circuit breaker's handle, in its highest position, shall not be more than what height above the floor or working platform?

5 ft 6 in
6 ft 0 in
6 ft 7 in
7 ft 0 in

NEC Reference: NEC 240.24(A)(1)

Question 17: A cartridge fuse has flat knife-blade contacts at each end, rather than cylindrical ferrule contacts. Per NEC 240.60(B), what does this indicate about the fuse's rating?

30 A or less
Exactly 60 A
60 A or less
Over 60 A

NEC Reference: NEC 240.60(B)

Question 18: Per NEC 240.22, overcurrent devices shall generally NOT be placed in series with which type of conductor?

Ungrounded (hot) conductors
Equipment grounding conductors
Grounded (neutral) conductors
All conductors equally

NEC Reference: NEC 240.22

Question 19: Per NEC 240.24(D), overcurrent devices shall not be located in the vicinity of easily ignitable material. Which specific example does the NEC give?

Attached garages
Clothes closets
Kitchen pantries
Utility rooms

NEC Reference: NEC 240.24(D)

Question 20: A circuit breaker has the marking "SWD" on its face plate. Per NEC 240.83(C), this breaker is listed and suitable for use as a switch on which type of circuit?

Motor circuits rated 1 HP or less
Fluorescent lighting circuits at 120V or 277V
Electric resistance heating circuits
HVAC compressor circuits

NEC Reference: NEC 240.83(D)

Question 21: Per NEC 240.10, supplementary overcurrent protection found inside luminaires or appliances does what?

May substitute for the branch-circuit device
Shall not substitute for branch-circuit protection
Must equal the branch-circuit device rating
Requires a separate disconnect per Article 430

NEC Reference: NEC 240.10

Question 22: Per NEC 240.4(B), when a conductor's ampacity does not correspond to a standard OCPD rating, the next higher standard device rating is permitted only if that next higher rating does not exceed what value?

400 A
600 A
800 A
1,000 A

NEC Reference: NEC 240.4(B)

Question 23: Per NEC 240.80, circuit breakers shall be what?

Operable by automatic means only
Capable of being opened and closed manually
Equipped with a key-operated interlock
Rated at a minimum of 30 A

NEC Reference: NEC 240.80

Question 24: Per NEC 240.51(B), Edison-base plug fuses shall be used only in what situation?

In all new residential installations
As replacements with no evidence of tampering/overfusing
In circuits up to 240 V
In motor circuits up to 2 HP

NEC Reference: NEC 240.51(B)

Question 25: Per NEC 240.54(C), once a Type S fuse adapter is installed in a fuseholder, what happens?

Removable with a screwdriver for changes
Non-removable, accepts only that ampere class
Accepts any ampere rating of Type S fuse
Removed before each replacement fuse

NEC Reference: NEC 240.54(C)

Question 26: What is a current-limiting overcurrent protective device?

A breaker with an adjustable long-time setting
A fuse that opens only after a 10-second delay
A device that limits normal load current to its rating
A device that, in its current-limiting range, cuts the fault current to well below the available value

NEC Reference: NEC 240.2

Question 27: Per NEC 240.4(G), overcurrent protection for conductors supplying motor loads is provided according to which NEC article?

Article 210
Article 220
Article 430
Article 440

NEC Reference: NEC 240.4(G)

Question 28: Per NEC 240.85, a circuit breaker with a slash voltage rating of "120/240V" may generally be applied on what type of system?

Ungrounded delta systems only
Corner-grounded delta systems only
Solidly grounded systems, voltage to ground under 120V
Any system under 240V line-to-line

NEC Reference: NEC 240.85

Question 29: Per the general rule in NEC 240.21(A), overcurrent protection must generally be provided for conductors where?

Where they terminate at the load
Where they receive their supply
At the midpoint of the run
Only at the main service disconnect

NEC Reference: NEC 240.21(A)

Question 30: Per NEC 240.4(D), what is the maximum overcurrent protection permitted for 12 AWG aluminum or copper-clad aluminum conductors?

15 A
20 A
25 A
30 A

NEC Reference: NEC 240.4(D)(4)

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 1 (NEC 240) — NEC 2020 Edition

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Overcurrent Protection Practice Test 1 (NEC 240) — NEC 2020 Edition — Question List

Question 1: Under the 10-foot feeder tap rule, the tap conductors must have an ampacity not less than what?

Question 2: Tap conductors that leave an enclosure or vault must generally have an ampacity of not less than what fraction of the overcurrent device rating protecting the feeder conductors?

Question 3: A branch-circuit-rated circuit breaker marked for use with 18 AWG copper supplies a continuous load of 5.6 A. What overcurrent protection rating may be used?

Question 4: How must an overcurrent device be connected to the ungrounded conductor it protects?

Question 5: In which location are overcurrent devices NOT permitted in dwelling units?

Question 6: What is the maximum voltage between conductors for which plug fuses may generally be used as overcurrent protection?

Question 7: Which of these is NOT a standard ampere rating for fuses and inverse-time circuit breakers in 240.6(A)?

Question 8: A circuit changes from a larger conductor to a smaller conductor with no overcurrent device at the change. The overcurrent device must protect which conductor?

Question 9: Under the 25-foot feeder tap rule, how must the tap conductors be protected from physical damage?

Question 10: Per NEC 240.4(D), what is the maximum overcurrent protection permitted for 14 AWG copper conductors in a branch circuit?

Question 11: Per NEC 240.4(D), what is the maximum overcurrent protection permitted for 12 AWG copper conductors?

Question 12: Conductors are protected by a 1,200 A overcurrent device. What is their minimum ampacity?

Question 13: A 25-foot tap conductor runs from a feeder to a subpanel. Per NEC 240.21(B)(2), the tap conductors must terminate in a single circuit breaker or set of fuses rated at no more than what?

Question 14: Per NEC 240.21(B)(2), for the 25-foot tap rule to apply, the tap conductor ampacity must be not less than what fraction of the upstream feeder overcurrent device rating?

Question 15: Per NEC 240.6(A), which of the following is NOT a standard ampere rating for fuses and fixed-trip circuit breakers?

Question 16: Per NEC 240.24(A), the center of the grip of a circuit breaker's handle, in its highest position, shall not be more than what height above the floor or working platform?

Question 17: A cartridge fuse has flat knife-blade contacts at each end, rather than cylindrical ferrule contacts. Per NEC 240.60(B), what does this indicate about the fuse's rating?

Question 18: Per NEC 240.22, overcurrent devices shall generally NOT be placed in series with which type of conductor?

Question 19: Per NEC 240.24(D), overcurrent devices shall not be located in the vicinity of easily ignitable material. Which specific example does the NEC give?

Question 20: A circuit breaker has the marking "SWD" on its face plate. Per NEC 240.83(C), this breaker is listed and suitable for use as a switch on which type of circuit?

Question 21: Per NEC 240.10, supplementary overcurrent protection found inside luminaires or appliances does what?

Question 22: Per NEC 240.4(B), when a conductor's ampacity does not correspond to a standard OCPD rating, the next higher standard device rating is permitted only if that next higher rating does not exceed what value?

Question 23: Per NEC 240.80, circuit breakers shall be what?

Question 24: Per NEC 240.51(B), Edison-base plug fuses shall be used only in what situation?

Question 25: Per NEC 240.54(C), once a Type S fuse adapter is installed in a fuseholder, what happens?

Question 26: What is a current-limiting overcurrent protective device?

Question 27: Per NEC 240.4(G), overcurrent protection for conductors supplying motor loads is provided according to which NEC article?

Question 28: Per NEC 240.85, a circuit breaker with a slash voltage rating of "120/240V" may generally be applied on what type of system?

Question 29: Per the general rule in NEC 240.21(A), overcurrent protection must generally be provided for conductors where?

Question 30: Per NEC 240.4(D), what is the maximum overcurrent protection permitted for 12 AWG aluminum or copper-clad aluminum conductors?

Key NEC References for This Test

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