NEC Article 240 Practice Questions: Overcurrent Protection

Standard device ratings, the small-conductor rule, next-size-up, and the tap rules — Article 240 is where conductor sizing meets breaker sizing on the exam.

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36 Article 240 questions in the bankWritten in the PSI computer-based exam formatEvery answer cites the NEC section

What Article 240 Covers on the Exam

Article 240 decides how conductors are protected: the standard ampere ratings in 240.6(A), the small-conductor limits of 240.4(D) (15 A for 14 AWG, 20 A for 12 AWG, 30 A for 10 AWG copper), the round-up allowance of 240.4(B), and the 10-ft/25-ft feeder tap rules in 240.21(B). Most Article 240 exam questions are two-step problems: find an ampacity, then pick the legal overcurrent device.

Tested subtopics from Article 240

Standard ampere ratings for fuses and breakers — 240.6(A)
Small-conductor rule for 14, 12, and 10 AWG — 240.4(D)
Next-higher-standard-rating allowance (800 A and below) — 240.4(B)
Feeder tap rules: 10-ft and 25-ft taps — 240.21(B)
Location and accessibility of overcurrent devices — 240.24

Drill a different article

36 questions in our bank cite Article 240. Practice the other high-yield articles too:

Art. 110 — General Requirements Art. 210 — Branch Circuits Art. 220 — Load Calculations Art. 230 — Services Art. 250 — Grounding and Bonding Art. 300 — Wiring Methods Art. 310 — Conductors & Ampacity Art. 314 — Boxes & Box Fill Art. 430 — Motors Art. 450 — Transformers Art. 680 — Swimming Pools & Spas

How to Study Article 240

Memorize the standard ratings sequence in 240.6(A) up to 100 A (15, 20, 25, 30, 35, 40, 45, 50, 60, 70, 80, 90, 100) and the 240.4(D) small-conductor caps — those two memorized facts answer a surprising share of questions without opening the book. For tap rules, learn the pattern: 10-ft taps need ampacity ≥ 1/10 of the protecting device, 25-ft taps need ≥ 1/3, and both must terminate in a single device.

Then put it under exam conditions: the free diagnostic scores you across every category and shows whether overcurrent protection is actually a weak area — or whether your study time belongs somewhere else.

Sample Questions (From Our Real Question Bank)

Here are 4 real questions from our question bank. The free diagnostic quiz has 10 more.

NEC NEC 240.4(D)(3)Overcurrent Protection

1. Per NEC 240.4(D), the overcurrent protection for 14 AWG copper conductors shall not exceed what ampere rating?

A10 amperes
B15 amperes
C20 amperes
D25 amperes

Show explanation

NEC 240.4(D)(3) specifies that 14 AWG copper conductors must be protected by overcurrent devices rated not more than 15 amperes.

NEC NEC 240.21(B)(1)Overcurrent Protection

2. Per NEC 240.21(B)(1), where a feeder tap conductor is not over 10 feet in length, the tap conductor ampacity must be at least what fraction of the feeder overcurrent device rating?

A1/2
B2/3
C3/4
DIt must equal the combined computed loads on the circuits supplied

Show explanation

NEC 240.21(B)(1) requires tap conductor ampacity to be not less than the combined computed loads on circuits supplied by the tap.

NEC NEC 240.6(A)Overcurrent Protection

3. Per NEC 240.6(A), which of the following is a standard ampere rating for fuses and inverse-time circuit breakers?

A55 amperes
B65 amperes
C80 amperes
D85 amperes

Show explanation

NEC 240.6(A) lists 80 amperes as a standard ampere rating; 55, 65, and 85 are not standard sizes.

NEC NEC 240.24(A)Overcurrent Protection

4. Per NEC 240.24(A), overcurrent devices shall be readily accessible. Which of the following is permitted as a location?

ABathrooms of dwelling units
BOver the steps of a stairway
CIn a closet used for storage
DIn a dedicated electrical room

Show explanation

NEC 240.24(A) permits overcurrent devices in electrical rooms. Bathrooms, stairway steps, and storage closets are not permitted locations.

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Frequently Asked Questions

What are the standard breaker sizes in NEC 240.6?

The standard ampere ratings in 240.6(A) include 15, 20, 25, 30, 35, 40, 45, 50, 60, 70, 80, 90, 100, 110, 125, 150, 175, 200, 225, 250, 300, 350, 400 and up. Exam questions often require rounding a calculated ampacity up or down to one of these standard ratings.

When can I round up to the next standard breaker size?

Per 240.4(B), where the conductor ampacity does not match a standard rating, the next higher standard device is permitted if the device is 800 A or less, the conductors are not part of a branch circuit supplying multiple receptacles, and the next size up does not exceed the article limits — 240.4(D) small-conductor caps still apply to 14, 12, and 10 AWG.

What is the 25-foot tap rule?

Per 240.21(B)(2), a feeder tap up to 25 feet long is permitted without overcurrent protection at the tap point if the tap conductor ampacity is at least one-third the rating of the device protecting the feeder, the tap terminates in a single breaker or set of fuses limiting the load to the tap ampacity, and the conductors are protected from physical damage.