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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 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 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.

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: 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: Per the 2026 NEC 240.87, the documentation supporting the chosen arc-energy reduction method must be:

Available to those authorized to inspect the installation
Sealed inside the gear and not removable
Stored only at the engineer of record's office
Submitted to the manufacturer for review

NEC Reference: NEC 2026 — 240.87(C)

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: Per the 2026 NEC, "instantaneous trip" used as an arc-energy reduction method must be set such that:

It is set higher than the available short circuit current
It is set lower than the available short circuit current
It is set equal to the breaker frame rating
It is disabled during normal operation

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

Question 8: A 1600A fused service has individual fuse blocks and an upstream breaker. Per the 2026 NEC 240.67, which method below is NOT permitted as an arc-energy reduction means for the fuses?

A non-thermal fuse with a clearing time of 0.07 seconds or less
Differential relaying
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: Per the 2026 NEC, "instantaneous override" used to satisfy 240.87 must be set such that the override pickup is no greater than what percentage of the available short-circuit current at the breaker terminals?

50%
80%
100%
125%

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

Question 14: A non-thermal fuse is selected to satisfy 240.67(B)(1) of the 2026 NEC. The clearing time at the available short-circuit current must be:

0.07 seconds or less
0.5 seconds or less
1.0 second or less
2.0 seconds or less

NEC Reference: NEC 2026 — 240.67(B)(1)

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: Per the 2026 NEC, the documentation supporting the chosen arc-energy reduction method may include:

Engineering documentation establishing reduced arc energy
Photos of the equipment label only
A verbal statement from the installer
No documentation is required

NEC Reference: NEC 2026 — 240.87(C)

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 IN

Question 21: In the motor branch-circuit one-line shown, the disconnect is located between the branch-circuit OCPD and the controller. Per the 2026 NEC, an arc-energy reduction means is required if the disconnect is rated at or above:

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

100A
600A
1200A
Always required regardless of size

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: Per the 2026 NEC, the arc-energy reduction means must remain in service:

Whenever workers could be exposed at the equipment
Only on weekends
Only at the time of commissioning
Only when the upstream service is fed by a generator

NEC Reference: NEC 2026 — 240.87

Question 25: A 2000A 480V switchboard has a labeled available short-circuit current of 50 kA. To use "instantaneous trip" as the arc-energy reduction method per the 2026 NEC, the breaker's instantaneous setting must be:

Set lower than 50 kA
Set higher than 50 kA
Set equal to the breaker frame
Disabled until a fault is detected

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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Key NEC References for This Test

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: Per the 2026 NEC 240.87, the documentation supporting the chosen arc-energy reduction method must be:

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

Question 7: Per the 2026 NEC, "instantaneous trip" used as an arc-energy reduction method must be set such that:

Question 8: A 1600A fused service has individual fuse blocks and an upstream breaker. Per the 2026 NEC 240.67, which method below is NOT permitted as an arc-energy reduction means for the fuses?

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: Per the 2026 NEC, "instantaneous override" used to satisfy 240.87 must be set such that the override pickup is no greater than what percentage of the available short-circuit current at the breaker terminals?

Question 14: A non-thermal fuse is selected to satisfy 240.67(B)(1) of the 2026 NEC. The clearing time at the available short-circuit current must be:

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: Per the 2026 NEC, the documentation supporting the chosen arc-energy reduction method may include:

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, the disconnect is located between the branch-circuit OCPD and the controller. Per the 2026 NEC, an arc-energy reduction means is required if the disconnect is rated at or above:

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: Per the 2026 NEC, the arc-energy reduction means must remain in service:

Question 25: A 2000A 480V switchboard has a labeled available short-circuit current of 50 kA. To use "instantaneous trip" as the arc-energy reduction method per the 2026 NEC, the breaker's instantaneous setting must be:

Key NEC References for This Test

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