NEC 240.6(A) · Overcurrent protection

How to read NEC 240.6(A) standard breaker sizes

What the standard-ratings table is for, how the 240.4(B) next-size-up rule uses it, and the mistakes that get feeders red-tagged — with a free link to the official table.

Need the actual list? Look up Table 240.6(A) in the free NFPA viewer →

How to use the standard-ratings table, step by step

Step	What you do	Why it matters
1	Find the conductor ampacity after all correction and adjustment factors	The rule compares the device to the final, derated ampacity — not the raw table value
2	Check whether that ampacity is itself a standard rating in Table 240.6(A)	If it is, that is your maximum device size — no bump
3	If not, find the next standard rating above it in the table	This is the only size the next-size-up rule can point to
4	Confirm the 240.4(B) conditions (see below)	The bump is conditional, and it stops at 800 A
5	Apply any specific limits that override the general rule	Small-conductor limits (240.4(D)), motor, and other article rules take precedence

Our own summary, not the code text. Look up Table 240.6(A) in the free NFPA viewer (nfpa.org/freeaccess) and verify against the NEC edition adopted by your AHJ.

When the 240.4(B) next-size-up rule applies (paraphrased)

Condition	In plain terms
Not a multi-outlet circuit for portable cord-and-plug loads	A general receptacle branch circuit does not get the bump
Ampacity does not already match a standard rating	If the ampacity lands on a standard size, use that size
Next standard size is 800 A or less	Above 800 A, 240.4(C) requires ampacity at least equal to the device rating

Our own summary, not the code text. Look up Table 240.6(A) in the free NFPA viewer (nfpa.org/freeaccess) and verify against the NEC edition adopted by your AHJ.

Worked example — 400 A feeder on one set of 500 kcmil copper

Input / step	Value	Source
Conductor	500 kcmil Cu, 75 °C terminations, no derating	Design
Ampacity	380 A	Table 310.16, 75 °C column
Is 380 A a standard rating?	No	Table 240.6(A)
Next standard rating above 380 A	400 A	Table 240.6(A)
240.4(B) conditions met? (feeder, ≤800 A)	Yes	240.4(B)
Result	400 A breaker permitted

Worked example values only. Look up the full tables in the free NFPA viewer.

Common field mistakes

Mistake	What to do instead
Bumping to the next size on a device over 800 A	Above 800 A there is no bump — add conductors or upsize them
Using the raw (non-derated) table ampacity	Apply temperature and bundling factors first, then look for the next standard size
Bumping a small conductor past its 240.4(D) limit	The small-conductor limits cap 14–10 AWG regardless of the next-size-up rule
Assuming a size is standard because it is sold	Nonstandard ratings are allowed, but only listed ratings count for "next standard size"
Assuming the low end of the list is the same in every edition	Check your adopted edition — the 2023 NEC revised the low ratings and which are fuse-only

Our own summary, not the code text. Look up Table 240.6(A) in the free NFPA viewer (nfpa.org/freeaccess) and verify against the NEC edition adopted by your AHJ.

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Why the standard-ratings list matters

Look up Table 240.6(A) in the free NFPA viewer. NFPA offers read-only access to current NEC editions at no cost. This page explains how to use the table; it does not reproduce it.

NEC 240.6(A) doesn’t tell you what breaker to install — it defines which ratings count as standard. That matters because several rules only let you step up to "the next higher standard rating." The most common is 240.4(B): when a conductor’s ampacity falls between standard sizes, you may use the next standard size up, as long as you’re at or below 800 A and it isn’t a multi-outlet circuit for portable loads.

Worked example. A feeder uses one set of 500 kcmil copper on 75 °C terminals with no derating. Per Table 310.16, that’s 380 A. 380 A isn’t a standard rating, and the next standard size in Table 240.6(A) is 400 A — so a 400 A breaker is permitted. Now suppose the same conductors are paralleled for a 1200 A service: three sets give 1140 A. That device is over 800 A, so 240.4(C) applies and 1140 A is not enough. You need a fourth set or larger conductors.

Before you pick the device, derate the conductors with the ampacity correction and adjustment factors guide, and respect the small-conductor limits covered in the wire size & breaker chart. After the device is chosen, the ground follows the breaker — see the equipment grounding conductor chart (NEC 250.122). Motor circuits have their own rules; start from the motor full-load current chart.

Edition note: the 2023 NEC revised the low end of the standard-ratings list and which small ratings are fuse-only — check the wording in the edition your AHJ enforces. Record final breaker sizes circuit by circuit on the panel schedule template; Field PM keeps panel schedules, inspections, and QA/QC together with the job.

FAQ

What does NEC Table 240.6(A) do?+

It lists the ampere ratings that the Code treats as "standard" for fuses and inverse-time circuit breakers. Other ratings are allowed, but rules that say "the next higher standard rating" — like 240.4(B) and several motor-circuit rules — point to this list. Look up Table 240.6(A) in the free NFPA viewer at nfpa.org/freeaccess.

What is the "next size up" rule?+

NEC 240.4(B) lets you protect a conductor with the next higher standard device rating when its ampacity does not match a standard rating, provided the circuit is not a multi-outlet branch circuit supplying cord-and-plug portable loads and the next size is 800 A or less. Example: 500 kcmil copper at 75 °C is 380 A per Table 310.16, so a 400 A device is permitted.

What happens above 800 amps?+

The bump goes away. Under 240.4(C), when the device is rated over 800 A, the conductor ampacity must be equal to or greater than the device rating. That usually means adding a parallel set or going to larger conductors.

Did the list change in the 2023 NEC?+

Yes — the 2023 edition revised the low end of Table 240.6(A), including which small ratings apply to breakers versus fuses only. If your jurisdiction is on 2017 or 2020, check that edition's wording before relying on a low-amp rating.

Are adjustable-trip breakers covered?+

Separately. 240.6(B) and (C) explain how to determine the rating of an adjustable-trip breaker — generally its maximum possible setting, unless access to the adjustment is restricted as the Code describes.

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