An ampere list is the standardized sequence of allowable overcurrent protective device (OCPD) ratings defined by electrical codes, dictating the exact trip thresholds you can legally install. When you calculate a circuit's required protection, this list changes your installation by forcing discrete sizing steps; if your math demands 26A of protection, you cannot buy a 26A breaker, so the list forces you up to the next standard size (30A), which in turn legally dictates the minimum wire gauge you must pull. People most commonly confuse the ampere list (the breaker's trip rating) with the wire's raw ampacity (the thermal limit of the copper), treating them as interchangeable when they are actually governed by different NEC articles.
The Standard Ampere List for Breakers and Fuses
Under NEC Article 240.6(A), the standard ampere ratings for fuses and fixed-trip circuit breakers are strictly defined. You cannot manufacture or install a breaker with an arbitrary trip point like 22A or 43A. The code mandates the following sequence for standard OCPDs:
For residential and light commercial work, 95% of your rough-in will rely on just five numbers from this list: 15, 20, 30, 40, and 50. If your calculated load falls between these numbers, NEC 240.4(B) allows the "next size up" rule: if your conductor ampacity doesn't match a standard breaker size, you are permitted to round up to the next available number on the ampere list, provided the calculated load does not exceed the conductor's actual ampacity.
Worked Example: Sizing a 240V Baseboard Heater Circuit
Let’s run the math on a real-world installation to see how the ampere list forces your hand on material selection.
- The Load: A 2000W, 240V electric baseboard heater.
- Base Current: I = P / V → 2000W / 240V = 8.33A.
- Continuous Load Factor: Because a heater can run for 3 hours or more, NEC 210.19 classifies it as a continuous load. We must multiply the base current by 125% (1.25).
- Sizing Current: 8.33A × 1.25 = 10.41A.
You need an OCPD rated for at least 10.41A. Looking at the ampere list, there is no 10A or 11A standard breaker. The next standard size up is 15A. Therefore, you install a 2-pole 15A breaker.
For the wire, NEC 240.4(D) restricts 14 AWG copper to a maximum 15A OCPD. While 14 AWG NM-B is legally sufficient here, standard ampacity charts show 14 AWG is right at its thermal ceiling.
Where You Meet the Ampere List in Practice
You will interact with this list constantly across three specific jobsite scenarios:
- HVAC Nameplates (MCA vs. MOCP): When wiring an air conditioner compressor, you look at the nameplate for Minimum Circuit Ampacity (MCA) and Maximum Overcurrent Protection (MOCP). If the MCA is 24A and the MOCP is 32A, you size your wire for 24A (10 AWG copper) but you must look at the ampere list to size the breaker. Since 32A isn't on the list, you round up to the next standard size: a 35A HACR breaker.
- Subpanel Feeders: If your calculated subpanel load is 83A, you cannot use an 85A breaker (not on the list). You step up to the 90A standard rating, which then requires you to pull 2 AWG copper or 1/0 AWG aluminum based on the 75°C termination column.
- Panel Schedules: Commercial panel schedules require you to log the exact OCPD rating. Inspectors will reject a schedule that lists a "22A breaker" because it violates the standardized ampere list.
Common Confusions: Wire Ampacity vs. Breaker Ratings
The most frequent mistake DIYers and junior apprentices make is confusing the wire's raw ampacity with the breaker's ampere rating, particularly regarding temperature columns.
Take 10 AWG THHN wire. If you look at the 90°C column in NEC Table 310.16, it shows an ampacity of 40A. However, NEC 110.14(C) dictates that unless your equipment is specifically rated for 90°C terminations (almost none are), you must use the 75°C column for equipment over 100A, and the 60°C column for equipment 100A and under. In the 60°C column, 10 AWG is only rated for 30A. Therefore, even though the copper could theoretically handle 40A, the termination limits restrict you to a 30A breaker on the ampere list.
Decision Tree: Picking Your Breaker and Wire
Use this decision matrix to terminate your calculations into exact material picks. This table assumes standard copper conductors (NM-B or THHN in conduit) and standard 80%-rated thermal-magnetic breakers.
| Calculated Continuous Load | Load × 1.25 (Sizing Value) | Ampere List Pick (Breaker) | Concrete Wire Pick (Copper) |
|---|---|---|---|
| 12.0A | 15.0A | 15A or 20A | 12 AWG NM-B (Default for mechanical strength) |
| 16.0A | 20.0A | 20A | 12 AWG NM-B |
| 24.0A | 30.0A | 30A | 10 AWG THHN / NM-B |
| 32.0A | 40.0A | 40A | 8 AWG THHN / NM-B |
| 40.0A | 50.0A | 50A | 6 AWG THHN / NM-B |
| 80.0A | 100.0A | 100A | 1 AWG THHN (or 1/0 AWG Aluminum) |
FAQ: Ampere List Edge Cases
Are 25A, 35A, and 45A breakers actually real?
Yes, they are explicitly listed in NEC 240.6(A). However, big-box hardware stores rarely stock them. You will typically need to order 25A, 35A, and 45A breakers from specialized electrical supply houses. They are most commonly used in commercial lighting panels and specific HVAC applications where a 30A or 40A breaker would nuisance-trip due to inrush current.
What if my equipment requires a 100% rated breaker?
Standard breakers on the ampere list are "80% rated" for continuous loads (which is why we multiply by 1.25). If you buy a specialized "100% rated" breaker and panel assembly, you do not apply the 1.25 multiplier. However, these are expensive, specialized commercial components and are almost never used in residential wiring.
Can I use a fuse instead of a breaker for these sizes?
The ampere list applies equally to fuses. If a motor circuit requires 35A overcurrent protection, you can use a 35A time-delay fuse in a fused disconnect switch just as you would a 35A breaker. Just ensure the fuse class (RK1, RK5, J, etc.) matches the disconnect's physical rejection pins.
