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NEC CODE NEC 2026

NEC 2026 Practice Test - Arc-Energy Reduction (240.67 / 240.87)

Practice test on the arc-energy reduction rules of the 2026 NEC. Covers when 240.67 (fuses) and 240.87 (circuit breakers) trigger, the seven approved reduction methods, documentation, and worker-exposure scope.

TOPICS COVERED

Overcurrent Protection

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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 NEC 2026 Practice Test - Arc-Energy Reduction (240.67 / 240.87) has 25 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.

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Topics covered: NEC articles 100, 210, 220, 240, 250, 300, 310, 430, and special occupancies.
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Questions: 25 multiple-choice, one correct answer each

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NEC 2026 Practice Test - Arc-Energy Reduction (240.67 / 240.87) — Question List

Question 1: Per the 2026 NEC, arc-energy reduction provisions of 240.87 apply to circuit breakers rated at or above what continuous current rating?

400 amperes
800 amperes
1200 amperes
2000 amperes

NEC Reference: NEC 2026 — 240.87

Question 2: Which of the following is NOT one of the listed arc-energy reduction methods in 240.87 of the 2026 NEC?

Zone-selective interlocking
Differential relaying
Time-current dependent overcurrent
Energy-reducing maintenance switching with local status indicator

NEC Reference: NEC 2026 — 240.87(B)

Question 3: Per the 2026 NEC, 240.67 arc-energy reduction applies to fuses with a continuous current rating equal to or above:

600 amperes
800 amperes
1200 amperes
4000 amperes

NEC Reference: NEC 2026 — 240.67

Question 4: A 2500A switchboard uses an energy-reducing maintenance switching method to satisfy 240.87 of the 2026 NEC. What additional feature does the code require at the switch?

A local status indicator
A locking pin only
A label that reads "DO NOT OPERATE"
A separate isolated power source

NEC Reference: NEC 2026 — 240.87(B)(3)

Question 5: Where a 1200 A or larger circuit breaker is installed, what documentation does 240.87(A) require?

Documentation submitted to the utility for approval
Documentation of the location of the circuit breaker(s), available to those authorized to design, install, operate or inspect
No documentation is required
A copy of the breaker invoice kept on the gear

NEC Reference: NEC 2026 — 240.87(A)

Question 6: Which of the following 480Y/277V switchboards is required by the 2026 NEC to have an arc-energy reduction means?

A 2500A bus fed by a 1000A main breaker
A 2000A bus fed by a 1600A main breaker
A 1200A bus fed by a 800A main breaker
A 600A bus fed by a 600A main breaker

NEC Reference: NEC 2026 — 240.87

Question 7: When an instantaneous trip setting is used as the arc energy reduction method, how must it be set?

Higher than the available short-circuit current
Less than the available arcing current
At 80% of the available short-circuit current
Equal to the breaker frame rating

NEC Reference: NEC 2026 — 240.87(B)(5)

Question 8: A 1600 A fused service must meet 240.67. Which of these is NOT a recognized way to comply?

Differential relaying
A fuse that clears in 0.07 s or less at the available arcing current
Lengthening the conductors to the load
Energy-reducing maintenance switching with local status indicator

NEC Reference: NEC 2026 — 240.67(B)

Question 9: Per the 2026 NEC, the arc-energy reduction system must be in service:

Only during the initial commissioning of the equipment
Only after a fault occurs
Whenever a worker could be exposed at the equipment
Only when external power is interrupted

NEC Reference: NEC 2026 — 240.87

Question 10: Differential relaying used to satisfy 240.87 of the 2026 NEC works by:

Comparing currents at the boundaries of a protected zone and tripping on imbalance
Sensing temperature inside the breaker housing
Limiting the let-through energy of an upstream fuse
Detecting voltage transients on the neutral

NEC Reference: NEC 2026 — 240.87(B)(2)

Question 11: A 1600A 480Y/277V switchboard uses zone-selective interlocking on the main breaker to satisfy 240.87 of the 2026 NEC. Zone-selective interlocking works by:

Coordinating with downstream breakers so the upstream device clears in-zone faults instantly and only delays when a downstream device sees the fault
Disabling the breaker during maintenance
Switching the source to a backup utility feed
Lowering the magnetic pickup permanently

NEC Reference: NEC 2026 — 240.87(B)(1)

Question 12: Per the 2026 NEC 240.87(B), an "energy-reducing active arc flash mitigation system" must operate within what time frame to count as a reduction method?

Faster than the breaker's normal clearing time so that incident energy is reduced
Only after the upstream breaker fails to operate
Within a fixed 100 ms window required by the NEC
Slower than the breaker so that nuisance trips are avoided

NEC Reference: NEC 2026 — 240.87(B)(4)

Question 13: When an instantaneous override is used as the arc energy reduction method, what must be true?

It is equal to the breaker continuous rating
It is no greater than 80% of the available short-circuit current
It is higher than the available short-circuit current
It is less than the available arcing current

NEC Reference: NEC 2026 — 240.87(B)(6)

Question 14: A fuse alone satisfies 240.67 if its clearing time at the available arcing current is not more than what?

0.07 seconds
0.5 seconds
1.0 second
2.0 seconds

NEC Reference: NEC 2026 — 240.67(B)

Question 15: Per the 2026 NEC, a 1600A circuit breaker that uses energy-reducing maintenance switching must:

Have a local status indicator that shows the reduced setting is engaged
Be remotely operated only
Have an audible alarm on every operation
Be replaced after each maintenance event

NEC Reference: NEC 2026 — 240.87(B)(3)

Question 16: Per the 2026 NEC, an "approved equivalent means" of arc-energy reduction in 240.87(B)(7) requires:

AHJ acceptance based on demonstrating equivalent reduction in arc energy
Manufacturer self-certification only
OSHA approval
No documentation is required

NEC Reference: NEC 2026 — 240.87(B)(7) / Article 100

Question 17: A 1500A switchboard with a 1500A main breaker and 600A and 800A sub-breakers serves a 480Y/277V system. Per the 2026 NEC, which breakers must have an arc-energy reduction means?

All three breakers
Only the 1500A main
Only the 800A sub-breaker
None — the rule applies only to gear over 5000A

NEC Reference: NEC 2026 — 240.87

Question 18: When evaluating arc-energy reduction methods per the 2026 NEC, the rating considered is:

The continuous current rating of the breaker
The frame size only
The interrupting rating only
The 30-cycle short-circuit withstand

NEC Reference: NEC 2026 — 240.87

Question 19: May the instantaneous trip setting of a breaker be lowered temporarily during maintenance to meet 240.87?

Yes, for breakers under 2000 A
No, temporary adjustment of the instantaneous trip is not permitted for this purpose
Yes, if it is restored afterward
Yes, if the change is logged

NEC Reference: NEC 2026 — 240.87(B)(5)

Question 20: NFPA 70E (the workplace electrical safety standard, referenced informally by the NEC) requires arc-flash hazard analysis. The 2026 NEC ties into NFPA 70E by:

Pointing to NFPA 70E in an informational note for incident-energy analysis
Replacing all of NFPA 70E with NEC text
Requiring an OSHA permit per breaker
Banning maintenance on energized gear

NEC Reference: NEC 2026 — 240.87 Informational Note

Question 21: In the motor branch-circuit one-line shown (10 HP motor), does 240.87 arc energy reduction apply to the branch-circuit breaker?

One-line diagram of a 10HP three-phase motor branch circuit with feeder, branch-circuit OCPD, disconnect, controller, overload relay, and motor

Only if the motor is over 5 HP
Yes, it applies to every motor circuit
No, 240.87 applies only to breakers whose trip setting can be 1200 A or more
Yes, because the disconnect is between the breaker and the controller

NEC Reference: NEC 2026 — 240.87

Question 22: The 2026 NEC 240.67 rule for fuses applies to which of the following service or feeder configurations?

Fuses rated 1200A or higher
All fuses regardless of rating
Only fuses on residential services
Only Class L fuses

NEC Reference: NEC 2026 — 240.67

Question 23: Per the 2026 NEC, the arc-energy reduction method for fuses listed in 240.67(B) may include:

Differential relaying
Increasing the conductor size
Adding a second main breaker
Using a different transformer turns ratio

NEC Reference: NEC 2026 — 240.67(B)

Question 24: What does 240.87(C) require for the arc energy reduction system?

Performance testing when first installed, with a written record available to the AHJ
No testing; the listing is enough
Annual replacement of the trip unit
Testing only after a fault occurs

NEC Reference: NEC 2026 — 240.87(C)

Question 25: A 2000 A, 480 V switchboard has an available bolted short-circuit current of 50 kA and a calculated arcing current of 28 kA. To use the instantaneous trip method, the setting must be below what?

40 kA, 80% of the bolted current
2000 A, the breaker rating
50 kA, the bolted short-circuit current
28 kA, the available arcing current

NEC Reference: NEC 2026 — 240.87(B)(5)

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.

NEC 2026 Practice Test - Arc-Energy Reduction (240.67 / 240.87)

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NEC 2026 Practice Test - Arc-Energy Reduction (240.67 / 240.87)

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NEC 2026 Practice Test - Arc-Energy Reduction (240.67 / 240.87) — Question List

Question 1: Per the 2026 NEC, arc-energy reduction provisions of 240.87 apply to circuit breakers rated at or above what continuous current rating?

Question 2: Which of the following is NOT one of the listed arc-energy reduction methods in 240.87 of the 2026 NEC?

Question 3: Per the 2026 NEC, 240.67 arc-energy reduction applies to fuses with a continuous current rating equal to or above:

Question 4: A 2500A switchboard uses an energy-reducing maintenance switching method to satisfy 240.87 of the 2026 NEC. What additional feature does the code require at the switch?

Question 5: Where a 1200 A or larger circuit breaker is installed, what documentation does 240.87(A) require?

Question 6: Which of the following 480Y/277V switchboards is required by the 2026 NEC to have an arc-energy reduction means?

Question 7: When an instantaneous trip setting is used as the arc energy reduction method, how must it be set?

Question 8: A 1600 A fused service must meet 240.67. Which of these is NOT a recognized way to comply?

Question 9: Per the 2026 NEC, the arc-energy reduction system must be in service:

Question 10: Differential relaying used to satisfy 240.87 of the 2026 NEC works by:

Question 11: A 1600A 480Y/277V switchboard uses zone-selective interlocking on the main breaker to satisfy 240.87 of the 2026 NEC. Zone-selective interlocking works by:

Question 12: Per the 2026 NEC 240.87(B), an "energy-reducing active arc flash mitigation system" must operate within what time frame to count as a reduction method?

Question 13: When an instantaneous override is used as the arc energy reduction method, what must be true?

Question 14: A fuse alone satisfies 240.67 if its clearing time at the available arcing current is not more than what?

Question 15: Per the 2026 NEC, a 1600A circuit breaker that uses energy-reducing maintenance switching must:

Question 16: Per the 2026 NEC, an "approved equivalent means" of arc-energy reduction in 240.87(B)(7) requires:

Question 17: A 1500A switchboard with a 1500A main breaker and 600A and 800A sub-breakers serves a 480Y/277V system. Per the 2026 NEC, which breakers must have an arc-energy reduction means?

Question 18: When evaluating arc-energy reduction methods per the 2026 NEC, the rating considered is:

Question 19: May the instantaneous trip setting of a breaker be lowered temporarily during maintenance to meet 240.87?

Question 20: NFPA 70E (the workplace electrical safety standard, referenced informally by the NEC) requires arc-flash hazard analysis. The 2026 NEC ties into NFPA 70E by:

Question 21: In the motor branch-circuit one-line shown (10 HP motor), does 240.87 arc energy reduction apply to the branch-circuit breaker?

Question 22: The 2026 NEC 240.67 rule for fuses applies to which of the following service or feeder configurations?

Question 23: Per the 2026 NEC, the arc-energy reduction method for fuses listed in 240.67(B) may include:

Question 24: What does 240.87(C) require for the arc energy reduction system?

Question 25: A 2000 A, 480 V switchboard has an available bolted short-circuit current of 50 kA and a calculated arcing current of 28 kA. To use the instantaneous trip method, the setting must be below what?

Key NEC References for This Test

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