Breaker Size Chart — NEC 240.6(A), 240.4(D) and 210.20

The breaker and the wire are two separate answers

Almost every breaker question online is really two questions wearing one hat. What device protects this circuit, and what conductor may sit behind it? The NEC answers them in different articles, with different arithmetic, and a circuit only passes inspection when both answers agree.

The device rating comes from Article 210 and Article 240: you size the overcurrent device to the load, then you check that the conductor can carry it. The conductor ampacity comes from Table 310.16, which is a thermal limit and nothing to do with the breaker except that the two numbers have to be compatible. A 30 A breaker on 14 AWG copper is wrong even though a 30 A breaker is a perfectly standard device, and 14 AWG copper is a perfectly normal conductor — they are simply not allowed to be paired. NEC 240.4(D) is the section that says so.

Standard breaker and fuse sizes — NEC Table 240.6(A)

The device you round up to has to be a standard rating. Table 240.6(A) lists them; nonstandard ratings exist and are permitted, but the next-size-up rule in 240.4(B) only reaches a standard rating, so the list is the list you actually shop from.

Those are the sizes that exist as both fuses and inverse-time circuit breakers. Five more ratings are standard for fuses only — 1, 3, 6, 10, 601 amperes — where 1 A through 10 A are the small control and instrument sizes and 601 A is the odd one out. There is no standard 6 A residential circuit breaker, which matters when a load calculation comes out at 5 A and someone reaches for the nearest number.

240.4(D) — the caps that override everything above

Five conductor sizes are capped regardless of what the ampacity table says. The cap is on the overcurrent device, it applies after any ambient or conductor-count correction factors, and unlike the general next-size-up rule it has no round-up allowance at all.

The practical effect is that 14 AWG copper is a 15 A conductor and no amount of 75°C or 90°C column reading changes that. 12 AWG copper is a 20 A conductor, which is why the standard residential 20 A circuit — kitchen counters, laundry, bathroom — uses it. And 10 AWG copper is a 30 A conductor, which is why a 30 A dryer or water heater circuit is wired in 10 AWG.

The 125% rule — NEC 210.20(A)

A continuous load is one expected to run for three hours or more. For those, the overcurrent device may not be smaller than the noncontinuous load plus 125% of the continuous load. The maths is trivial and the consequences are not: 125% is a 25% oversizing of the device, which is exactly what turns an 18.75 A water heater into a 23.4 A requirement and therefore a 25 A breaker.

The 125% is not padding and it is not a manufacturer's preference. A breaker holds its rating in a specific ambient environment; a device run at exactly its rating for hours drifts toward its thermal trip. The code buys the difference in the device rating rather than hoping the enclosure stays cool.

What the rule does not say is that every appliance counts as continuous. A range, a dryer and a well pump cycle on and off, and are treated as noncontinuous for this purpose. Water heaters, EV chargers and most lighting are the continuous ones — which is why a 4,500 W water heater gets a 25 A minimum while a 4,500 W dryer element would not.

240.4(B) — when a breaker may be bigger than the wire

Because devices only come in standard sizes and ampacities do not, there are cases where a conductor's ampacity falls between two standard device ratings. 240.4(B) permits the next standard size up, provided three conditions hold: the conductors are not part of a branch circuit supplying more than one receptacle for cord-and-plug portable loads; the ampacity does not itself correspond to a standard rating; and the next size selected does not exceed 800 A.

A worked case shows how narrow the permission is. 8 AWG copper is 40 A at 60°C, and 40 A is not a device whose next standard rating is 50 A — it is 45 A. So 240.4(B) does not let 8 AWG copper sit on a 50 A breaker at 60°C terminations, and the correct answer is 6 AWG copper (55 A). Put the same conductor on a 45 A breaker and the round-up does apply, because 45 A is the very next standard rating above 40 A. The same conductor, the same table cell, two different answers decided entirely by which device you are trying to fit.

422.11(E)(3) — why the same water heater has two right answers

210.20(A) sets the floor for the device. For a single non-motor-operated appliance, 422.11(E)(3) sets a ceiling: the branch circuit overcurrent protection may not exceed 150% of the appliance rated current, rounded up to the next standard rating if 150% does not land on one. For a 4,500 W, 240 V heater that ceiling is 28.1 A, so a 30 A device is legal as well as a 25 A one.

That is the whole explanation for the argument you will find in every forum thread on the subject. One electrician says 25 A because that is the 210.20(A) minimum; another says 30 A because that is the common field answer and 422.11(E)(3) permits it. Both are quoting the code correctly and quoting different sections of it. The lookup on this page shows you both numbers, so you can see the range rather than one end of it.

Worked example — the 4,500 W water heater, step by step

• Current. I = P ÷ E = 4,500 W ÷ 240 V = 18.75 A.
• Continuous load (210.20(A)). 18.75 × 1.25 = 23.44 A minimum device rating.
• Round up to a standard size (240.6(A)). The next rating above 23.44 A is 25 A.
• Upper limit (422.11(E)(3)). 18.75 × 1.5 = 28.13 A, rounded up to a standard rating = 30 A.
• Conductor. 10 AWG copper is 30 A at 60°C, which covers the 25 A device with room, and 240.4(D) caps 10 AWG at 30 A — so 10 AWG copper is the answer for either device. The lookup also returns 8 AWG aluminium (35 A at 60°C) if you switch materials.

That is the entire calculation, and it is worth doing by hand once because it is the same five steps for a dryer, a range, a hot tub or an EV charger.

Worked example — a 40 A EV charger

An EV charger is treated as a continuous load, so 625.41 requires the branch circuit overcurrent device to be sized at not less than 125% of the maximum load. A charger rated 40 A therefore needs at least 50 A of device, and 50 A is already a standard rating — no rounding needed. The conductor is the one that may carry a 50 A device: 6 AWG copper at 60°C (55 A), or 8 AWG copper if every termination is listed for 75°C, where 8 AWG is exactly 50 A. Most installers take 6 AWG, because a 100 ft run to a garage usually fails voltage drop before it fails ampacity — that part of the job belongs to the voltage drop calculator.

Breaker and wire for common appliances

The rows below are the circuits a residential electrician sizes every week. The device column is the code answer for the situation in the first column, and the basis column names the section it comes from — so when a number disagrees with something you read elsewhere, you can check which section each of you is quoting.

Two of those rows deserve a warning attached. The first is HVAC: Article 440 deliberately permits a device larger than the conductor ampacity, because the breaker there is providing short-circuit and ground-fault protection only — the equipment's own overload protection is inside the unit. A 40 A breaker on a circuit with a 28 A minimum circuit ampacity is not a mistake; it is what the nameplate asks for. Never "correct" an HVAC circuit down to the conductor ampacity.

The second is the range and dryer rows, where the receptacle standard and the code meet. A new dryer circuit is four-wire on a NEMA 14-30, and a new range circuit is four-wire on a NEMA 14-50; the three-wire allowance in 250.140 is for existing installations only. Running a new three-wire circuit and bonding the appliance frame to the neutral is the single most common error in this part of the trade, and no inspector will pass it.

Wire size by breaker rating — and the ground that goes with it

"What size wire for a 30 amp breaker" and its 50 A and 60 A siblings are the most-asked conductor questions in the trade, and the honest answer needs three numbers, not one: the conductor by the termination column you are actually using, the same conductor in aluminium if you are running aluminium, and the equipment grounding conductor, which is sized from the breaker and not from the current carrying conductors.

Read the table as: pick the column your terminations are listed for, then take the conductor. The 60 °C column is the default for circuits of 100 A or less unless the breaker, lugs, receptacles and connectors are all listed for 75 °C — that is 110.14(C)(1), and it is why the internet "disagrees" about these answers. A 60 A circuit takes 4 AWG copper at 60 °C (70 A) but only 6 AWG copper at 75 °C (65 A), while a 50 A circuit is 6 AWG at 60 °C (55 A) and 8 AWG — exactly 50 A, no headroom — at 75 °C. When in doubt, take the 60 °C column. It is never wrong, only occasionally larger than necessary.

The EGC column comes from a completely different table. NEC 250.122 sizes the equipment grounding conductor from the rating of the overcurrent device, not from the ungrounded conductors, so every breaker from 30 A through 60 A asks for the same 10 AWG copper ground (8 AWG aluminium). A 15 A circuit takes 14 AWG Cu and a 20 A circuit takes 12 AWG Cu. The catch is 250.122(B): if you increase the ungrounded conductors for any reason — the classic one being a long feeder upsized for voltage drop — the EGC has to be increased in the same proportion. That is the step people miss on a 200 ft garage feed, and it is the reason a voltage drop calculation changes the ground wire, not just the hots.

240.4(D) still caps the low end. The table shows 10 AWG copper carrying a 30 A breaker — legal, and exactly at the 30 A cap with no room to round up. The aluminium answer for 30 A is 8 AWG, because 10 AWG aluminium is capped at 25 A and the cap has no next-size-up allowance. This is the same rule already printed in the 240.4(D) table above, and it is the one that decides 30 A circuits in aluminium.

One worked line to check by hand: a 60 A breaker feeding a subpanel, 75 °C terminations. Table 310.16 gives 6 AWG copper = 65 A in the 75 °C column, which covers 60 A with 5 A spare. The EGC from Table 250.122 is 10 AWG copper. If the run is long enough that voltage drop forces the hots up to 4 AWG, 250.122(B) scales the ground up with them, so the 10 AWG answer stops being correct. The subpanel wire size guide works that exact arithmetic end to end.

How many outlets can you put on one circuit?

There is no single number, because the code answers two different questions. For a commercial or non-dwelling branch circuit, NEC 220.14(I) counts a receptacle outlet at 180 volt-amperes per yoke — a duplex counts once, because it is one yoke — so the maximum is a matter of division. For a dwelling, the same 180 VA rule does not apply at all: 220.14(J) sends the receptacle load to 220.41 and Table 220.42, calculated at 3 VA per square foot, and sets no yoke limit on a general-use circuit. Almost every page on the internet quotes the commercial number and then tells a homeowner it is a limit. It is not.

The arithmetic is the whole trick. A 20 A / 120 V circuit has 20 × 120 = 2,400 VA available; each yoke is 180 VA; 2,400 ÷ 180 = 13.33, and because you cannot install two-thirds of an outlet the answer is 13. That single division is where the well-worn "13 outlets on a 20 amp circuit" rule comes from. A 15 A circuit gives 15 × 120 = 1,800 VA ÷ 180 = exactly 10. A quick sanity check: 13 yokes × 180 VA = 2,340 VA, which is under the 2,400 VA line; a 14th would push it to 2,520 VA and fail.

Two refinements matter. First, the figure assumes the circuit is not carrying a continuous load. General branch circuits should not carry more than 80% continuously (the 125% rule in 210.19(A) and 210.20(A), applied above), so a 20 A circuit loaded continuously works out at 16 A × 120 V = 1,920 VA ÷ 180 = 10 yokes, and a 15 A circuit at 12 A × 120 V = 1,440 VA ÷ 180 = 8 yokes. Second, in a dwelling none of it applies: a 2,500 ft² house computes its receptacle load at 2,500 × 3 VA = 7,500 VA, which is 62.5 A spread across as many general-use circuits as the designer chooses — roughly 55 small-load receptacles if you assume 180 VA, split over about four 15 A circuits. That is a design split, not a code cap.

Where the dwelling rules do bite is in the required circuits. NEC 210.11(C)(1) demands two 20 A small-appliance branch circuits for the kitchen, dining and pantry receptacles, and 210.11(C)(2) demands one 20 A laundry circuit. Those circuits come with their own appliance-load arithmetic (Table 220.52) and are separate from the general-use calculation. The appliance rows above name the section behind each one.

Common mistakes with breaker sizing

• Sizing the breaker to the wire instead of the load. 12 AWG copper can be protected at 20 A, but that does not mean a 12 A load needs a 20 A device. Size the load, apply 125% where it applies, then round up.
• Applying 125% to everything. Ranges, dryers and pumps cycle; treating them as continuous oversizes the circuit and can push a receptacle circuit past a 240.4(D) cap.
• Using the 75°C column with 60°C terminations. 110.14(C) limits the circuit to the weakest termination. 8 AWG copper is a 40 A conductor or a 50 A one depending on that, and the difference decides whether 240.4(B) is even relevant.
• Assuming 240.4(B) always saves a size. It only reaches the very next standard rating, it stops at 800 A, and it does not apply to a circuit feeding several cord-and-plug receptacles.
• Ignoring 240.4(D) after derating. The 14/12/10 AWG caps apply to the corrected ampacity, not the base table cell. In a hot attic a 20 A circuit can need a conductor larger than 12 AWG even though the device stays at 20 A.
• Treating a bigger breaker as safer. The device protects the conductor; a device larger than the conductor is rated for converts an overload into a fire instead of a trip.
• Fighting the nameplate on HVAC. For air conditioning and refrigeration equipment the marked MOP is the answer, and the standard rules are superseded by Article 440.
• Forgetting the AFCI/GFCI device requirements. Those choose a device type, not a rating, and they live in 210.8 and 210.12 — a correctly sized 20 A breaker still fails if the circuit needs GFCI protection and does not have it.

Breaker size FAQ

Where these numbers came from

Table 240.6(A) was verified 2026-09-26 against the NEC text reproduced at electricallicenserenewal.com, in both its 2014 paragraph form and its 2017 table form, including the five additional fuse-only ratings. The 240.4(B) text quoted above, including the three conditions and the 2023 sentence on adjustable-trip devices, comes from the same source. The 240.4(D) caps were verified 2026-09-14 and are already used by the ampacity chart and the voltage drop calculator. The appliance rows are assembled from the sections named in each row — 210.19(A)(3), 210.23(C), 220.54, 220.55, 250.140, 422.11(E)(3), 440.22(A), 440.4(B) and 625.41 — cross-checked on 2026-09-26 against EC&M and IAEI commentary on Article 210 and Mike Holt material on Articles 422 and 440. The breaker-to-conductor and EGC rows were assembled from the Table 310.16 set verified 2026-09-25 and NEC Table 250.122, verified 2026-10-15 against the TEP engineering standard PDF (docs.tep.com/doc/ESR/SR-453.pdf), extracted twice, and cross-checked against eepower and turn2engineering reproductions of the table. The 180 VA outlet arithmetic follows NEC 220.14(I) with the dwelling exception in 220.14(J)/220.41, verified 2026-10-13 and re-confirmed 2026-10-16. Local amendments and the authority having jurisdiction always win.

Related pages

• Wire ampacity chart — NEC Table 310.16 — the conductor half of every pairing on this page, with the ambient and bundle derating factors
• Conduit fill chart — NEC Chapter 9 — how many conductors fit the raceway before ampacity even comes into it
• Voltage drop & wire size calculator — for the runs where distance, not ampacity, decides the size
• What size wire for a 100 amp subpanel? — the same rules applied to a feeder, with a distance table
• Reference tables — every code table on the site, with its source and verification date