The standard breaker amp chart maps overcurrent protection devices (breakers) to the minimum allowable wire gauge (AWG) based on ampacity. For the most common residential branch circuits, the baseline rule is simple: a 15-amp breaker requires 14 AWG copper wire, a 20-amp breaker requires 12 AWG, a 30-amp breaker requires 10 AWG, and a 50-amp breaker requires 6 AWG. However, pulling a single wire gauge for a given breaker without considering insulation temperature ratings, continuous loads, and conduit fill can lead to tripped breakers, melted insulation, or a failed inspection.
This reference guide provides the complete ampacity data sourced directly from the National Electrical Code (NEC), explains how to select the correct temperature column for your specific installation, and details the derating factors that modify these base values in real-world conditions.
How to Read the Standard Breaker Amp Chart
Before sizing a circuit, you must understand how the NEC structures ampacity tables. The primary reference is NEC Table 310.16, which lists allowable ampacities for insulated conductors rated up to 2000 volts. The table is divided into temperature columns: 60°C (140°F), 75°C (167°F), and 90°C (194°F).
Which column applies to your installation? This is the most common point of failure for DIYers and junior electricians. According to NEC 110.14(C), the temperature rating of the lowest-rated component in the circuit dictates the column you must use. For circuits rated 100 amps or less, or for wire sizes 14 AWG through 1 AWG, you must use the 60°C column for breaker sizing. This applies even if you are pulling 90°C-rated THHN wire through conduit, because standard residential breakers and receptacles are typically only rated for 60°C or 75°C terminations. For circuits over 100 amps or wire sizes 1/0 AWG and larger, you may use the 75°C column.
NEC 240.4(D) places a hard cap on overcurrent protection for small conductors, regardless of their 90°C ampacity. You cannot protect 14 AWG copper with anything larger than 15A, 12 AWG with more than 20A, or 10 AWG with more than 30A, with very few specific exceptions (like motor starting currents).
Complete NEC Breaker and Wire Ampacity Chart
The following table provides the standard breaker sizes mapped to the minimum required copper and aluminum wire gauges. This data synthesizes NEC Table 310.16 and the small conductor rules of 240.4(D). Bookmark this section for quick-jump lookups on the most frequently queried residential and light commercial values (highlighted in bold).
| Breaker Size (Amps) | Copper (60°C Column) | Copper (75°C Column) | Aluminum (75°C Column) | Common Application |
|---|---|---|---|---|
| 15A | 14 AWG | 14 AWG | 12 AWG | General lighting, bedroom/bathroom receptacles |
| 20A | 12 AWG | 12 AWG | 10 AWG | Kitchen/bathroom small appliance circuits, outdoor GFCI |
| 25A | 12 AWG | 10 AWG | 8 AWG | Rare in residential; specific commercial HVAC |
| 30A | 10 AWG | 10 AWG | 8 AWG | Dryers, RV outlets, water heaters, window AC units |
| 40A | 8 AWG | 8 AWG | 6 AWG | Electric ranges, ovens, cooktops |
| 50A | 6 AWG | 6 AWG | 4 AWG | Hot tubs, spas, Level 2 EV chargers, subpanels |
| 60A | 6 AWG | 6 AWG | 4 AWG | Large subpanels, heavy-duty workshop equipment |
| 70A | 4 AWG | 4 AWG | 3 AWG | EV chargers, commercial HVAC |
| 80A | 4 AWG | 3 AWG | 2 AWG | Large subpanels, tankless electric water heaters |
| 90A | 3 AWG | 3 AWG | 1 AWG | Feeder circuits |
| 100A | 3 AWG | 4 AWG | 2 AWG | Small subpanels, detached garages |
| 125A | 2 AWG | 1 AWG | 1/0 AWG | Main panels, large subpanels |
| 150A | 1 AWG | 1/0 AWG | 2/0 AWG | Standard modern residential main service |
| 200A | 2/0 AWG | 2/0 AWG | 4/0 AWG | Large residential main service, farm panels |
Note: Aluminum wire sizing assumes 75°C rated terminations and is generally not used for branch circuits under 50A in modern residential construction due to termination torque requirements and historical oxidation issues.
Derating Factors and What the Chart Cannot Tell You
While the chart above provides the baseline ampacity, it assumes ideal conditions: an ambient temperature of 86°F (30°C) and no more than three current-carrying conductors in a raceway or cable. What the table cannot tell you is how environmental factors and continuous loads reduce the actual current-carrying capacity of your wire.
How derating rows modify the base value: When you pull wire through a hot attic or bundle multiple circuits in a single conduit, you must apply derating factors from NEC Table 310.15(B)(1) and Table 310.15(C)(1). For example, if you have 4 to 6 current-carrying conductors in a single conduit, you must multiply the wire's base ampacity by 80%. If you are using 8 AWG THHN copper (rated 55A at 90°C), the derated ampacity becomes 44A (55 x 0.80). Because 44A is not a standard breaker size, NEC 240.4(B) allows you to round up to the next standard size, which is a 45A breaker (if available) or more commonly, you must drop to a 40A breaker to maintain a safety margin.
If a load is expected to run for 3 hours or more continuously (like an EV charger, a commercial lighting array, or a space heater), the breaker and wire must be sized at 125% of the continuous load. A 40-amp continuous EV charger requires a 50-amp breaker (40 x 1.25 = 50) and wire sized for 50 amps, even if the device's nameplate says 40A.
Additionally, the chart does not account for voltage drop. For runs exceeding 100 feet, you may need to increase the wire gauge by one or two sizes to ensure the voltage at the receptacle remains within the acceptable 3% to 5% drop threshold recommended by the NEC for branch and feeder circuits combined. Always calculate voltage drop for long runs to prevent motor burnout and dimming lights.
Breaker Amp Chart FAQ
Can I put a 20-amp breaker on 14 AWG wire?
No. Under NEC 240.4(D), 14 AWG copper wire is strictly limited to a maximum 15-amp overcurrent protection device. Installing a 20-amp breaker on 14 AWG wire creates a severe fire hazard, as the wire can overheat and melt its insulation before the breaker trips. If you need a 20-amp circuit, you must upgrade the entire circuit to 12 AWG wire.
What size breaker and wire do I need for a 50-amp hot tub?
A standard 50-amp hot tub requires a 50-amp double-pole GFCI breaker and 6 AWG copper wire (using the 60°C column for standard NM-B cable, or 8 AWG THHN if run in conduit and terminated at 75°C rated lugs). However, if the hot tub's control system draws a continuous load exceeding 32 amps, you must apply the 125% continuous load rule, which may require upsizing to a 60-amp breaker and 4 AWG wire. Always verify the manufacturer's spec sheet.
Why is my 90°C THHN wire limited to the 60°C column for breaker sizing?
While THHN wire insulation is rated for 90°C, the terminations (the lugs inside your breaker panel and your receptacles) are typically only rated for 60°C or 75°C. NEC 110.14(C) dictates that the circuit's ampacity is limited by the lowest temperature rating of any connected component. You can use the 90°C column strictly for applying derating factors (like ambient heat or conduit fill), but the final derated ampacity cannot exceed the 60°C or 75°C column value for breaker sizing.
Does this breaker amp chart apply to aluminum wire for service entrances?
Yes, but you must use the 75°C column for aluminum, as modern aluminum alloys (like AA-8000 series) and anti-oxidant pastes are rated for 75°C terminations. For a standard 200-amp residential service entrance, the chart shows you need 4/0 AWG aluminum wire. For detailed safety protocols on aluminum terminations, refer to OSHA wiring design and protection standards, which mandate specific torque values to prevent arcing and thermal expansion failures.
