7.2 Overcurrent Device Selection (Art 240)

Article 240 on the Prov Outline

Within the 8-item Services/Feeders/OCP block, overcurrent questions reward clean lookups in Article 240. Arkansas Journeyman candidates must connect conductor ampacity (from §7.1) to device rating without mixing branch-circuit folklore, motor rules, or tap exceptions until the stem actually calls for them.

Tab 240.4, 240.4(B), 240.4(C), 240.4(D), 240.5, 240.6, and the start of 240.21 before exam day.

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Purpose of Overcurrent Protection

Overcurrent devices protect conductors and equipment against overload and short-circuit/ground-fault currents. For feeder and branch conductors, the default exam path is:

1. Establish conductor ampacity (after adjustment/correction and termination limits).
2. Select an OCPD that protects those conductors under 240.4.
3. Use a standard rating from 240.6(A) unless a specific rule allows otherwise.
4. Place the device so conductors are protected at the point they receive supply — unless a 240.21 tap/transformer exception applies (covered in §7.3).

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Conductors — 240.4 Overview

240.4 requires conductors (other than flexible cords, flexible cables, and fixture wires) to be protected against overcurrent in accordance with their ampacities specified in 310.14 (ampacity tables/rules) unless otherwise permitted or required in 240.4.

Key subsections you will open constantly:

Do not jump to next-size-up until you confirm you are in the ≤800 A world and that 240.4(D) does not cap the rating for 14/12/10 AWG.

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Next Higher Standard Rating — 240.4(B)

For 800 amperes or less, 240.4(B) permits the next higher standard overcurrent device rating (above the ampacity of the conductors being protected) when all of the following are met (paraphrased — verify exact text):

• The conductors being protected are not part of a branch circuit supplying more than one receptacle for cord-and-plug-connected portable loads.
• The ampacity of the conductors does not correspond to a standard OCPD rating in 240.6(A).
• The next higher standard rating selected does not exceed 800 A.

Exam workflow example:

• Conductor ampacity after all factors = 95 A.
• Standard ratings near 95 A include 90 A and 100 A (240.6(A)).
• Ampacity does not match a standard size exactly → 240.4(B) may allow 100 A if the other conditions are satisfied.
• If the conductors were 14 AWG copper branch conductors, 240.4(D) would still limit you — next-size-up cannot override the small-conductor caps.

Trap: Next-size-up is not a universal right. Multi-receptacle cord-and-plug branch circuits and >800 A feeders are classic denial paths.

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Over 800 Amperes — 240.4(C)

Where the overcurrent device is rated over 800 A, the ampacity of the conductors it protects must be equal to or greater than the rating of the overcurrent device. You cannot round up past conductor ampacity on large feeders the way 240.4(B) sometimes allows on smaller circuits.

Prov pattern: a stem with 1000 A or 1200 A protection and conductors whose ampacity is slightly under the device rating is testing 240.4(C) — upsize conductors, do not apply next-size-up logic from 240.4(B).

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Small Conductors — 240.4(D)

Unless specifically permitted elsewhere, overcurrent protection shall not exceed the following for small copper conductors (confirm aluminum rows and exceptions in the section):

These limits are among the highest-frequency “gotchas” when candidates try to apply 240.4(B) to NM-B or THHN branch conductors. Exceptions exist for specific applications (certain motor circuits, HVAC, tap rules, etc.) — open the referenced sections only when the stem identifies those applications.

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Standard Ampere Ratings — 240.6

240.6(A) lists standard ampere ratings for fuses and inverse-time circuit breakers, including common sizes such as 15, 20, 25, 30, 35, 40, 45, 50, 60, 70, 80, 90, 100, 110, 125, 150, 175, 200, 225, 250, 300, 350, 400, 450, 500, 600, 700, 800, 1000, 1200, 1600, 2000, 2500, 3000, 4000, 5000, and 6000 amperes (verify the published list in your NEC — do not rely on memory for obscure mid-range sizes).

240.6(B)/(C) address additional adjustable-trip and fuse configurations. For Prov JW items, the usual ask is: “Which of the following is a standard rating?” or “Which next standard size applies under 240.4(B)?”

If an option shows a nonstandard rating like 95 A as a breaker size, treat it as suspicious unless the stem is discussing ampacity rather than device rating.

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Location of Overcurrent Devices — 240.21 Lead-In

240.21 general rule: overcurrent protection shall be provided in each ungrounded circuit conductor and shall be located at the point where the conductors receive their supply, except as permitted in 240.21(A) through (H) (branch-circuit taps, feeder taps, transformer secondaries, etc.).

For §7.2 selection questions, remember:

• Feeder OCPDs generally sit at the supply end of the feeder.
• You cannot run long unprotected feeders just because the load-end panel has a main breaker — unless a tap rule or other 240.21 permission applies.
• Service OCPD location remains governed by Article 230 (see Chapter 6); do not answer service main location with 240.21 tap lengths.

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Supplementary and Equipment Protection Distinctions

240.10 distinguishes supplementary overcurrent protection (not a substitute for branch-circuit protection). 110.10 and equipment listing/SCCRs address available fault current and interrupting ratings — a correctly sized ampere rating can still be wrong if the device’s interrupting rating is below available fault current. When a stem gives available fault current, check interrupting rating / SCCR themes, not only 240.4 ampacity pairing.

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Feeder vs Branch Device Selection

Same Article 240 engine, different inputs:

• Branch circuits: also obey Article 210 ratings (15, 20, 30, 40, 50 A common multioutlet rules) and 240.4(D) for small conductors.
• Feeders: ampacity from 215.2 + 310.16, then protect with 240.4; multioutlet receptacle limits in 240.4(B) matter less for pure feeder stems, but tap and continuous-load rules still apply.

If the stem says “feeder conductors have an ampacity of 175 A,” look for a 175 A standard device or a lawful 240.4(B) next size — not a dwelling branch-circuit 20 A habit.

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Timed Open-Book Tips for §7.2

1. Find conductor ampacity first.
2. Check 240.4(D) if 14/12/10 AWG.
3. If ≤800 A and ampacity ≠ standard size, test 240.4(B) conditions.
4. If >800 A, enforce 240.4(C) — no rounding above ampacity.
5. Pick the rating from 240.6(A).
6. Confirm location / taps only when the stem mentions supply-end distance or tap conductors.

That order prevents the most common Prov miss: applying next-size-up on a small conductor or on a >800 A feeder.