Breaker Size Chart | NEC 240.6 & Wire Gauge

Quick Answer

Quick Answer: For common copper branch-circuit lookups, 14 AWG -> 15A, 12 AWG -> 20A, and 10 AWG -> 30A under the NEC 240.4(D) small-conductor path. Standard NEC 240.6 breaker ratings commonly checked next include 15, 20, 25, 30, 35, 40, 45, and 50A, then 60A and larger ratings. Use the calculator after this table when continuous loads, conductor derating, motors, HVAC, listed equipment, or local AHJ rules change the answer.

Wire gauge to breaker size — common copper reference:

Run the Breaker Sizing Calculator when the question is not a simple wire-gauge lookup. A general branch circuit, a motor circuit, an equipment-nameplate circuit, and a panel-capacity question do not use the same decision flow.

Breaker Calculator Follow-Up After the Table

Use this sequence after the direct table lookup when the job has conditions that can change the breaker result:

1. Run the Breaker Sizing Calculator with load current, continuous-duty status, load type, and conductor count.
2. If the question starts with a conductor or wire gauge, open the Wire Size Calculator and keep voltage drop, material, insulation, and terminal temperature with the result.
3. If ambient heat, conductor grouping, or terminal rating changes the usable current, verify the Ampacity Calculator before selecting the breaker.
4. Use the Breaker Size Chart only after the calculator path identifies the load category, conductor basis, and standard OCPD review point.

The NEC 240.6 and wire-gauge tables below are reference checks. They are not a standalone breaker-size finder for motors, HVAC equipment, EVSE, transformers, listed equipment, or panel-capacity changes.

NEC 240.6 Standard Breaker Sizes Reference

Standard Ampere Ratings

Use this table as a reference for standard OCPD ratings after the applicable NEC path is known. Some adopted editions and product categories include additional ratings, so always confirm the code edition and equipment listing before final selection.

Common standard OCPD ratings checked under NEC 240.6(A) include:

Key Rule: The next-standard-size review is conditional. Only round up when the applicable NEC path, conductor size, equipment listing, and AHJ review allow it.

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):

NEC 240.4(D) Small Conductor Exception: 14, 12, and 10 AWG copper conductors are commonly limited to 15A, 20A, and 30A respectively. Do not apply the next-standard-size-up rule until the adopted NEC path, conductor size, and equipment instructions support it.

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.

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 should not be used for small branch circuits unless the adopted NEC edition, product listing, and termination equipment explicitly support the installation. Large aluminum service, feeder, and branch-circuit conductors require proper conductor sizing, compatible terminations, antioxidant practices where specified, and torque verification.

Wire Gauge to Breaker Size Chart

Quick Reference: Copper Wire at 60°C

*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:

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

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

Calculator handoff: Enter the continuous and non-continuous portions separately in the breaker sizing calculator. Use the adjusted result with the standard-size reference only after the load category is clear.

Residential Breaker Sizing Chart

Common Residential Circuits

→ Calculate your load first: Residential Load Calculator

Motor Circuit Breaker Sizing

NEC 430.52 Motor Branch Circuit Protection

Motor FLC Reference (3-Phase, 460V):

→ Use Full Load Current Calculator for NEC table FLC values.

Calculator Workflow Examples

Example 1: Basic Residential Circuit

Try this path: General branch circuit, normal indoor ambient, copper conductor, known circuit rating.

Run the load basis through the Breaker Sizing Calculator, then verify conductor ampacity and terminal rating before treating the branch-circuit breaker as selected.

Example 2: Hot Attic Installation

Try this path: Existing conductor in a hot attic where ambient temperature changes the ampacity basis.

Use the Ampacity Calculator first, then return to the breaker workflow with the adjusted ampacity rather than selecting from the unadjusted conductor row.

Example 3: Conduit with Multiple Conductors

Try this path: Raceway with more than three current-carrying conductors.

Use the Conduit Fill Calculator and Ampacity Calculator before coordinating the breaker with the adjusted conductor result.

Common Mistakes to Avoid

AFCI and GFCI Requirements

NEC 210.12 — Arc-Fault Circuit Interrupter (AFCI) Protection

Common NEC 210.12 AFCI review covers 120V, single-phase, 15A and 20A branch circuits supplying outlets or devices in many dwelling-unit locations:

AFCI breaker types: Combination-type AFCI detects both series and parallel arcing. Branch/feeder AFCI breakers and AFCI receptacles may be permitted depending on the adopted NEC edition, product listing, installation method, and AHJ interpretation. Verify the adopted NEC 210.12 language before choosing the protection method.

NEC 210.8 — Ground-Fault Circuit Interrupter (GFCI) Protection

Common NEC 210.8 GFCI review covers 125V through 250V, single-phase, 15A through 50A receptacles in many dwelling-unit locations:

AFCI vs GFCI: Class A GFCI devices used for personnel protection are intended to trip at low ground-fault current levels, commonly around 5 mA; equipment-protection devices can use higher thresholds. AFCI protects against arcing faults in wiring that may not trip standard breakers. Device class, product listing, adopted NEC edition, and AHJ requirements control the final protection method.

Related Calculators

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

Use this page as a workflow, not a standalone permission table:

• Identify whether the breaker protects a general branch circuit, motor, listed equipment, feeder, or panel change.
• Separate continuous and non-continuous load portions before choosing a standard rating.
• Confirm conductor material, terminal temperature rating, ambient temperature, and conductor-count adjustment.
• Use the standard-size, small-conductor, and ampacity references only after the calculator path identifies the project basis.

FAQ

What size wire do I need for a 30 amp breaker?

Enter the load, conductor material, terminal temperature rating, ambient conditions, and run length in the wire-size and ampacity calculators before selecting a conductor. A reference row is not enough when voltage drop, temperature, or conductor count changes the basis.

Can I use a 20 amp breaker on 14 gauge wire?

Treat this as a small-conductor protection check. Use the breaker workflow and the NEC 240.4(D) reference table rather than overriding the conductor-protection path from a single answer snippet.

What is the next size up rule?

NEC 240.4(B) can allow a next standard OCPD rating when the conductor ampacity does not exactly match a standard size, but only when the applicable conditions are satisfied. Use the breaker calculator result with the conductor-protection notes before applying it.

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?

Enter continuous and non-continuous portions separately, then carry the adjusted current into the standard-size and conductor-protection review. The correct result also depends on conductor ampacity, equipment labeling, available fault current, and the adopted NEC edition.