Quick Answer
Wire gauge to breaker size — NEC 240.4(D) hard limits:
Match breaker to wire ampacity per NEC 240.4:
NEC standard breaker sizes start at 15, 20, 25, 30, 35, 40, 45, and 50 A before stepping into 60 A and larger ratings under NEC 240.6.
| Wire Gauge | Max Breaker (Copper, 60°C) | Common Use |
|---|---|---|
| 14 AWG | 15A | Lighting circuits |
| 12 AWG | 20A | Receptacle circuits |
| 10 AWG | 30A | Small appliances, A/C |
| 8 AWG | 40A | Electric range, dryer |
| 6 AWG | 55A | Large appliances |
| 4 AWG | 70A | Subpanels |
| 2 AWG | 95A | Service entrance |
→ Use the Breaker Sizing Calculator for your specific load.
NEC 240.6 Standard Breaker Sizes
Standard Ampere Ratings
NEC 240.6(A) defines standard circuit breaker sizes:
| Category | Available Sizes |
|---|---|
| Small | 15, 20, 25, 30, 35, 40, 45, 50 A |
| Medium | 60, 70, 80, 90, 100, 110, 125 A |
| Large | 150, 175, 200, 225, 250, 300 A |
| Extra Large | 350, 400, 450, 500, 600 A |
| Industrial | 700, 800, 1000, 1200, 1600, 2000, 2500, 3000, 4000, 5000, 6000 A |
Key Rule: Select the next standard size UP if calculated ampacity falls between standard ratings (per NEC 240.4(B)).
NEC 240.4 Conductor Protection Table
Maximum Overcurrent Protection for Copper Conductors
Based on NEC Table 310.16, 60°C column (most common for residential; 75°C column applies when terminals are listed for 75°C):
| AWG | Ampacity (60°C) | Max Breaker | Max Breaker (Next Size Up Rule) |
|---|---|---|---|
| 18 | 7A | 7A* | Not typically used |
| 16 | 10A | 10A* | Not typically used |
| 14 | 15A | 15A | 15A (small conductors exception) |
| 12 | 20A | 20A | 20A (small conductors exception) |
| 10 | 30A | 30A | 30A (small conductors exception) |
| 8 | 40A | 40A | 45A |
| 6 | 55A | 55A | 60A |
| 4 | 70A | 70A | 70A |
| 3 | 85A | 85A | 90A |
| 2 | 95A | 95A | 100A |
| 1 | 110A | 110A | 110A |
| 1/0 | 125A | 125A | 125A |
| 2/0 | 145A | 145A | 150A |
| 3/0 | 165A | 165A | 175A |
| 4/0 | 195A | 195A | 200A |
NEC 240.4(D) Small Conductor Exception: 14, 12, and 10 AWG must NOT exceed 15A, 20A, and 30A respectively. The next-standard-size-up rule (240.4(B)) only applies to conductors 8 AWG and larger.
Maximum Overcurrent Protection for Aluminum Conductors
Based on NEC Table 310.16, 75°C column (aluminum conductors, USE-2, XHHW-2, THHN/THWN-2):
Note: Most equipment terminals are rated 75°C, so the 75°C column applies for most aluminum installations. Aluminum conductors must be terminated in connectors listed for aluminum. Anti-oxidant compound required per manufacturer instructions.
| AWG / kcmil | Ampacity (75°C) | Max OCPD | Equivalent Copper | Common Use |
|---|---|---|---|---|
| 10 AWG Al | 30A | 30A | 8 AWG Cu | Not recommended for 30A branch circuits |
| 8 AWG Al | 40A | 40A | 6 AWG Cu | Range, dryer (with Al-rated connectors) |
| 6 AWG Al | 50A | 50A | 4 AWG Cu | Subpanel feeder, large A/C |
| 4 AWG Al | 65A | 65A | 3 AWG Cu | Service entrance, feeder |
| 2 AWG Al | 90A | 90A | 1 AWG Cu | 100A service entrance |
| 1/0 AWG Al | 120A | 120A | 2/0 AWG Cu | 125A service |
| 2/0 AWG Al | 135A | 150A* | 3/0 AWG Cu | 150A service |
| 4/0 AWG Al | 180A | 200A* | 350 kcmil Cu | 200A service entrance |
| 350 kcmil Al | 255A | 300A* | 500 kcmil Cu | 300A service |
| 500 kcmil Al | 310A | 350A* | 700 kcmil Cu | 350A service |
Next standard size up per NEC 240.4(B) when ampacity doesn't match a standard OCPD rating.
Why aluminum conductors are common for service entrances: Aluminum is lighter, less expensive, and has lower thermal expansion concerns when properly terminated. However, aluminum must NEVER be used for small branch circuits (12 AWG or smaller) due to connection failure risks from thermal cycling and oxidation. The 2026 NEC permits aluminum for services, feeders, and large branch circuits (≥8 AWG) with proper terminations.
Wire Gauge to Breaker Size Chart
Quick Reference: Copper Wire at 60°C
| Wire Size | Description | Max Breaker | Typical Application |
|---|---|---|---|
| 14 AWG | Smallest residential | 15A | Lighting, low-load outlets |
| 12 AWG | Standard residential | 20A | General purpose receptacles |
| 10 AWG | Heavy duty | 30A | Dryers, A/C units, water heaters |
| 8 AWG | Large loads | 40A | Electric ranges, large A/C |
| 6 AWG | Subfeeder | 55A (or 60A*) | Subpanels, large equipment |
| 4 AWG | Service | 70A | Small service entrance |
| 3 AWG | Service | 85A (or 90A*) | Service entrance |
| 2 AWG | Service | 95A (or 100A*) | 100A service |
| 1/0 AWG | Large service | 125A | 125A service |
| 2/0 AWG | Large service | 145A (or 150A*) | 150A service |
| 4/0 AWG | Residential main | 195A (or 200A*) | 200A service |
*Next standard size up per NEC 240.4(B), when ampacity doesn't match standard breaker size.
Temperature Correction Factor Table
NEC Table 310.15(B)(1) - Ambient Temperature Correction
For ambient temperatures above 30°C (86°F), derate conductor ampacity:
| Ambient Temp °C | Ambient Temp °F | 60°C Conductor | 75°C Conductor | 90°C Conductor |
|---|---|---|---|---|
| 21-25 | 70-77 | 1.08 | 1.05 | 1.04 |
| 26-30 | 79-86 | 1.00 | 1.00 | 1.00 |
| 31-35 | 88-95 | 0.91 | 0.94 | 0.96 |
| 36-40 | 97-104 | 0.82 | 0.88 | 0.91 |
| 41-45 | 106-113 | 0.71 | 0.82 | 0.87 |
| 46-50 | 115-122 | 0.58 | 0.75 | 0.82 |
| 51-55 | 124-131 | 0.41 | 0.67 | 0.76 |
| 56-60 | 133-140 | — | 0.58 | 0.71 |
Formula:
Corrected Ampacity = Base Ampacity × Temperature Correction Factor
Example: 12 AWG (20A at 60°C) in 40°C ambient:
Corrected = 20A × 0.82 = 16.4A → Use 15A breaker
Conductor Fill Derating Table
NEC Table 310.15(C)(1) - More Than 3 Current-Carrying Conductors
| Number of Conductors | Ampacity Adjustment |
|---|---|
| 4-6 | 80% |
| 7-9 | 70% |
| 10-20 | 50% |
| 21-30 | 45% |
| 31-40 | 40% |
| 41 and above | 35% |
Formula:
Derated Ampacity = Base Ampacity × Fill Adjustment Factor
Example: 12 AWG with 6 conductors in conduit:
Derated = 20A × 0.80 = 16A → Use 15A breaker
Continuous vs Non-Continuous Load Sizing
NEC 210.20(A) Branch Circuit Sizing
| Load Type | Sizing Rule | Formula |
|---|---|---|
| Non-continuous | 100% of load | Breaker ≥ Load |
| Continuous (3+ hours) | 125% of load | Breaker ≥ Load × 1.25 |
| Mixed | Sum of factors | Breaker ≥ (Cont × 1.25) + Non-cont |
Example Calculation:
| Load | Type | Calculation |
|---|---|---|
| 16A lighting | Continuous | 16 × 1.25 = 20A |
| 8A receptacles | Non-continuous | 8 × 1.00 = 8A |
| Total | 28A → 30A breaker |
Residential Breaker Sizing Chart
Common Residential Circuits
| Circuit | Wire Size | Breaker | Notes |
|---|---|---|---|
| Lighting | 14 AWG | 15A | Max 12 outlets per circuit |
| General receptacles | 12 AWG | 20A | Max 10 outlets per circuit |
| Kitchen counter | 12 AWG | 20A | Two 20A circuits required |
| Bathroom | 12 AWG | 20A | Dedicated or shared per code |
| Laundry | 12 AWG | 20A | Dedicated circuit required |
| Dishwasher | 12 AWG | 20A | Dedicated circuit |
| Disposal | 12 AWG | 20A | May share with dishwasher |
| Refrigerator | 12 AWG | 20A | Dedicated recommended |
| Microwave | 12 AWG | 20A | Dedicated circuit |
| Electric dryer | 10 AWG | 30A | 30A 4-wire circuit |
| Electric range | 8/6 AWG | 40-50A | Based on nameplate |
| Water heater | 10 AWG | 30A | Typical 4500W unit |
| A/C (small) | 10 AWG | 30A | Check unit nameplate |
| A/C (large) | 8 AWG | 40A | Check unit nameplate |
| EV charger L2 | 6 AWG | 50A | 40A continuous load |
→ Calculate your load first: Residential Load Calculator
Motor Circuit Breaker Sizing
NEC 430.52 Motor Branch Circuit Protection
| Motor Type | Maximum Breaker Size |
|---|---|
| Standard induction | 250% of FLC |
| Wound rotor | 150% of FLC |
| Synchronous | 200% of FLC |
| DC (constant voltage) | 150% of FLC |
| DC (variable voltage) | 150% of FLC |
Motor FLC Reference (3-Phase, 460V):
| HP | FLC (A) | Max Breaker (250%) |
|---|---|---|
| 1 | 2.1 | 6A |
| 3 | 4.8 | 15A |
| 5 | 7.6 | 20A |
| 7.5 | 11 | 30A |
| 10 | 14 | 35A |
| 15 | 21 | 60A |
| 20 | 27 | 70A |
| 25 | 34 | 90A |
| 30 | 40 | 100A |
| 40 | 52 | 150A |
| 50 | 65 | 175A |
| 75 | 96 | 250A |
| 100 | 124 | 350A |
→ Use Full Load Current Calculator for NEC table FLC values.
Worked Examples
Example 1: Basic Residential Circuit
Given: 20A kitchen counter circuit at 75°F ambient
Solution:
- Load: 20A (continuous - kitchen lighting/appliances)
- Continuous load factor: 20A × 1.25 = 25A
- Wire selection: 10 AWG (30A capacity) to handle 25A
- Breaker: 20A (circuit is designated 20A, wire supports it)
Example 2: Hot Attic Installation
Given: 12 AWG wire in 120°F (49°C) attic
Solution:
- Base ampacity: 20A (12 AWG, 60°C)
- Temperature correction (46-50°C): 0.58
- Corrected ampacity: 20A × 0.58 = 11.6A
- Maximum breaker: 10A (or use 75°C rated wire with 25A × 0.75 = 18.75A → 15A breaker)
Example 3: Conduit with Multiple Conductors
Given: 6 current-carrying 12 AWG conductors in conduit
Solution:
- Base ampacity: 20A
- Conductor fill factor (4-6): 0.80
- Adjusted ampacity: 20A × 0.80 = 16A
- Maximum breaker: 15A
Common Mistakes to Avoid
| Mistake | Why It's Wrong | Correct Approach |
|---|---|---|
| Using 75°C ratings with 60°C terminals | Terminal limits conductor rating | Use 60°C column for most residential |
| Ignoring continuous load 125% rule | Breaker will trip | Size for 125% of continuous loads |
| Forgetting conduit fill derating | Overheated conductors | Apply fill factors when >3 conductors |
| Using next-size-up for small conductors | NEC 240.4(D) prohibits this | 14/12/10 AWG limited to 15/20/30A max |
AFCI and GFCI Requirements
NEC 210.12 — Arc-Fault Circuit Interrupter (AFCI) Protection (2026 NEC)
AFCI protection is required for all 120V, single-phase, 15A and 20A branch circuits supplying outlets in the following dwelling unit locations:
| Location | AFCI Required | NEC Reference |
|---|---|---|
| Bedrooms (all) | ✔ Yes | 210.12(A)(1) — original requirement |
| Living rooms, parlors, dens | ✔ Yes | 210.12(A)(2) |
| Dining rooms, family rooms | ✔ Yes | 210.12(A)(3) |
| Kitchens | ✔ Yes | 210.12(A)(4) |
| Laundry areas | ✔ Yes | 210.12(A)(5) |
| Sunrooms, recreation rooms | ✔ Yes | 210.12(A)(6) |
| Hallways, closets | ✔ Yes | 210.12(A)(7) |
| Basements (finished) | ✔ Yes | 210.12(A)(8) |
| Dormitory units, hotel guest rooms | ✔ Yes | 210.12(B) |
| Garages, outdoors, bathrooms | ✖ No (GFCI instead) | GFCI per 210.8 applies |
AFCI breaker types: Combination-type AFCI (detects both series and parallel arcing) is the type required by NEC 210.12. Branch/feeder AFCI breakers also satisfy the requirement. AFCI receptacles may be used at the first outlet in lieu of a panel breaker in retrofit situations per 210.12(D). The 2026 NEC extends AFCI to virtually all living spaces in a dwelling unit.
NEC 210.8 — Ground-Fault Circuit Interrupter (GFCI) Protection (2026 NEC)
GFCI protection is required for all 125V through 250V, single-phase, 15A through 50A receptacles in the following locations:
| Location | GFCI Required | Voltage/Amperage | NEC Reference |
|---|---|---|---|
| Bathrooms (all) | ✔ Yes | 125–250V, 15–50A | 210.8(A)(1) |
| Garages (including attached) | ✔ Yes | 125–250V, 15–50A | 210.8(A)(2) |
| Outdoors | ✔ Yes | 125–250V, 15–50A | 210.8(A)(3) |
| Crawl spaces (≤grade level) | ✔ Yes | 125–250V | 210.8(A)(4) |
| Unfinished basements | ✔ Yes | 125–250V | 210.8(A)(5) |
| Kitchens (countertop within 6 ft of sink) | ✔ Yes | 120V, 15/20A | 210.8(A)(6) |
| Kitchen islands and peninsulas | ✔ Yes | 120V | 210.8(A)(7) |
| Boathouses | ✔ Yes | 125–250V | 210.8(A)(8) |
| Bathtub and shower areas | ✔ Yes | 125–250V | 210.8(A)(9) |
| Laundry areas | ✔ Yes | 125–250V | 210.8(A)(10) |
| Indoor damp/wet locations | ✔ Yes | 125–250V | 210.8(A)(11) |
| Dishwashers (dedicated circuits) | ✔ Yes | 120V | 210.8(D) |
| EV charging (in garages) | ✔ Yes | 125–250V | 210.8(A)(2) applies |
AFCI vs GFCI: GFCI protects against ground faults (≥30 mA leakage to ground → trip within ~25 ms). AFCI protects against arcing faults in wiring that may not trip standard breakers. Both protections can be combined in a dual-function AFCI/GFCI breaker (one device satisfies both NEC 210.8 and 210.12 requirements where both apply, such as kitchen circuits).
Related Calculators
| Calculator | Use When... |
|---|---|
| Breaker Sizing Calculator | Screening a standard breaker review point |
| Wire Size Calculator | Determining conductor size for load |
| Ampacity Calculator | Checking conductor ampacity after temperature or conductor-count adjustment |
| Residential Load Calculator | Calculating total service load |
| Voltage Drop Calculator | Checking wire length adequacy |
After the Breaker Chart Lookup
Use the chart result as a screening point, not as the final project record. Before updating a panel schedule or selecting equipment, carry the same load basis through the Breaker Sizing Calculator and document the standard-size choice in the Breaker Size Chart. If conductor temperature rating, ambient temperature, or more than three current-carrying conductors changes the ampacity basis, review the NEC Ampacity Chart and run the adjusted value through the Ampacity Calculator before treating the breaker and conductor pair as coordinated. If the work changes an existing panel, update the Panel Load Schedule Chart so circuit identity, breaker poles, spare spaces, and panel limitations stay visible.
When the breaker serves equipment with an interrupting-rating or SCCR question, continue to the Short Circuit Calculator before treating the breaker selection as complete. Field installation still depends on the adopted NEC edition, listed equipment instructions, conductor terminal ratings, available fault current, and AHJ review.
Summary
Quick Reference Rules:
- 14 AWG → 15A max (NEC 240.4(D))
- 12 AWG → 20A max (NEC 240.4(D))
- 10 AWG → 30A max (NEC 240.4(D))
- Larger wire → Next standard size up allowed (NEC 240.4(B))
- Continuous loads → 125% sizing (NEC 210.20(A))
- Hot locations → Apply temperature correction
- Multiple conductors → Apply fill derating
FAQ
What size wire do I need for a 30 amp breaker?
For a 30A breaker, use minimum 10 AWG copper wire (NEC 240.4(D)). For runs over 100 feet, consider upsizing to 8 AWG to account for voltage drop.
Can I use a 20 amp breaker on 14 gauge wire?
No. Per NEC 240.4(D), 14 AWG wire is limited to 15A overcurrent protection maximum. Using a 20A breaker would create a fire hazard.
What is the next size up rule?
NEC 240.4(B) allows using the next standard breaker size up when the conductor ampacity doesn't match a standard size (e.g., 55A ampacity → 60A breaker). This does NOT apply to 14, 12, and 10 AWG conductors.
Why does continuous load require 125% sizing?
Continuous loads (running 3+ hours) generate sustained heat in conductors and breakers. The 125% factor provides thermal margin to prevent nuisance tripping and extends equipment life.
How do I size a breaker for multiple loads?
Add all non-continuous loads at 100%, add all continuous loads at 125%, then select the next standard breaker size equal to or greater than the total.