Standard Breaker Sizes Chart (NEC): Breaker-to-Wire Sizing Guide
Choosing a circuit breaker sounds simple until you're standing in front of a panel trying to match a load, a wire size, and a code book. This chart-style guide puts every standard NEC breaker size in one place, shows you the breaker-to-wire pairings electricians actually use, and walks through the 125% continuous-load rule that decides most real-world sizing questions. Bookmark it — it's the same reference our counter staff at Portlandia Electric Supply uses when customers call in.
The NEC standard breaker sizes chart
NEC 240.6(A) defines the standard ampere ratings for fuses and inverse-time circuit breakers. Anything outside this list is a non-standard or specialty trip unit:
| Standard breaker sizes (amps) | Typical residential/commercial use |
|---|---|
| 15, 20 | Lighting and general-purpose receptacle circuits |
| 25, 30 | Water heaters, dryers (30A), small AC units, RV/TT-30 |
| 35, 40, 45, 50 | Ranges, ovens, EV chargers, hot tubs, subpanels |
| 60, 70, 80, 90, 100 | Subpanels, large EV chargers, small services |
| 110, 125, 150, 175, 200 | Main breakers, large subpanels, small commercial |
| 225, 250, 300, 350, 400 | Commercial services, large feeders |
| 450, 500, 600, 700, 800 | Large commercial/industrial mains |
| 1000, 1200, 1600, 2000 | Industrial switchgear |
| 2500, 3000, 4000, 5000, 6000 | Utility-scale / large facility mains |
If your calculated load lands between two sizes, NEC 240.4(B) generally lets you round up to the next standard size — as long as the conductors' ampacity is at least equal to the load, the load isn't continuous above the conductor rating, and the next size up doesn't exceed 800A.
Breaker-to-wire size chart (copper, 75°C terminations)
The breaker protects the wire, not the appliance. These are the standard pairings using THHN/THWN-2 copper at 75°C ampacity with the NEC 240.4(D) small-conductor limits applied:
| Breaker size | Minimum copper wire (THHN/THWN-2) | Aluminum equivalent | Common application |
|---|---|---|---|
| 15A | 14 AWG | 12 AWG | Lights, general outlets |
| 20A | 12 AWG | 10 AWG | Kitchen/bath/garage receptacles |
| 30A | 10 AWG | 8 AWG | Dryer, water heater, RV outlet |
| 40A | 8 AWG | 6 AWG | Range, EV charger (32A) |
| 50A | 8 AWG* | 6 AWG | Range, EV charger (40A), hot tub |
| 60A | 6 AWG | 4 AWG | Subpanel, EV charger (48A) |
| 100A | 3 AWG | 1 AWG | Subpanel, small service |
| 125A | 1/0 AWG | 2/0 AWG | Large subpanel |
| 150A | 1/0 AWG | 3/0 AWG | Small commercial feeder |
| 200A | 3/0 AWG | 250 kcmil | Residential main service |
*50A breakers pair with 8 AWG copper only when the 75°C ampacity (50A) applies; with 60°C terminations (NM-B/Romex), 6 AWG is required. When in doubt, upsize the wire.
How to size a breaker: the 125% rule
Most sizing mistakes come from ignoring continuous loads. NEC defines a continuous load as one that runs for 3 hours or more — EV chargers, water heaters, and lighting all qualify. The rule:
- Continuous loads: multiply the load by 125%, then pick the next standard breaker size at or above that number.
- Non-continuous loads: the breaker just needs to be at or above the load (and protect the conductor).
- The wire must always be protected: conductor ampacity ≥ breaker rating (with the 240.4(B) round-up exception).
Worked example: EV charger circuit
You're installing a 32-amp Level 2 EV charger. EV charging is a continuous load (NEC 625.41), so: 32A × 1.25 = 40A. A 40A breaker with 8 AWG copper THHN in conduit is the correct minimum. Want the faster 40-amp charger? 40A × 1.25 = 50A breaker, still 8 AWG copper at 75°C — but 6 AWG NM-B if you're running Romex. Stepping up to a 48-amp charger (the sweet spot for most home installs) needs a 60A breaker and 6 AWG copper. See our EV charger circuit size chart for the full table, and our wire ampacity chart for conductor ratings at every gauge.
Worked example: electric range
A residential range draws a nameplate 40A. Ranges cycle on and off, so they're non-continuous: a 40A breaker and 8 AWG copper covers it. If the nameplate says 45A, round up to a 50A breaker per NEC 240.4(B).
Common mistakes to avoid
- Upsizing the breaker to stop nuisance trips. If a 20A breaker trips, the fix is finding the overload or fault — never a 30A breaker on 12 AWG wire. That's a fire in a wall.
- Forgetting 240.4(D). Regardless of insulation ampacity, 14 AWG is capped at 15A, 12 AWG at 20A, and 10 AWG at 30A overcurrent protection (motor and welder circuits excepted).
- Mixing conductor metals without checking terminations. Aluminum branch circuits need CO/ALR-rated devices and antioxidant compound.
- Ignoring panel bus rating. A 100A subpanel fed from a 100A breaker is fine; a 100A breaker in a 100A main panel leaves nothing for the rest of the house. Do a load calculation first.
Breaker types: standard, GFCI, AFCI, and dual-function
The amp rating is only half the spec — the *type* of breaker matters just as much to code and safety:
- Standard (thermal-magnetic): the default for most circuits. Trips on overload (thermal) and short circuit (magnetic).
- GFCI: required by NEC 210.8 in kitchens, bathrooms, garages, outdoors, basements, laundry, and anywhere near water. Protects people from shock by tripping on a 4–6 mA ground fault.
- AFCI: required in most living areas (bedrooms, living rooms, hallways) by NEC 210.12. Detects dangerous arcing — the loose-connection failure mode that causes a large share of residential electrical fires.
- Dual-function (AFCI+GFCI): one breaker covers both requirements — the clean answer for laundry rooms, kitchens, and any remodel where both rules apply.
- GFPE (ground-fault protection of equipment): higher 30 mA trip threshold, used for heat trace and some EV/pool equipment.
Two practical notes from the counter: first, breaker types are panel-specific — a Square D Homeline breaker does not belong in a Siemens panel, even if it physically clicks in. Match the breaker to the panel's label. Second, tandem (half-width) breakers are only legal in panel positions marked for them; cramming tandems everywhere to dodge a panel upgrade fails inspection and overheats bus stabs.
Frequently asked questions
What are the NEC standard breaker sizes?
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 amps (NEC 240.6(A)).
What size breaker do I need for a 30-amp load?
If it's continuous, 30A × 1.25 = 37.5A → round up to a 40A breaker with 8 AWG copper. If non-continuous, a 30A breaker with 10 AWG copper is correct.
Can I put a 20-amp breaker on 14-gauge wire?
No. NEC 240.4(D) limits 14 AWG to 15A overcurrent protection. Use 12 AWG for a 20A circuit.
What size wire for a 100-amp subpanel?
3 AWG copper THHN (100A at 75°C) or 1 AWG aluminum, plus a grounding conductor. Many installers upsize to 2 AWG or 1/0 for voltage drop on runs over 100 feet.
Is a double-pole 30A breaker 60 amps?
No. Each leg is 30A at 240V — it supplies 30 amps of 240V load (7,200 watts), not 60.
Get the right gear
Portlandia Electric Supply stocks breakers, disconnects, wire, and panels for residential through commercial work. Browse our Safety and Protection collection for DC and AC breakers like the MidNite Solar MNEPV30-300 circuit breaker and the MidNite 175A panel-mount DC breaker, or the wider Electrical Components collection for conductors, conduit, and fittings. Pairing a standby generator with a new panel? See our automatic transfer switches. Need a hand matching a breaker to a load? Call the counter — we do this all day.