Breaker GuideNEC 2023 · 2026 · Updated Apr 2026

20 Amp Breaker: Wire Size and Uses

A 20A breaker requires minimum 12 AWG copper or 10 AWG aluminum at 120V. Maximum continuous load: 16A (80% rule). Standard size per NEC 240.6(A).

Copper12 AWG

Aluminum10 AWG

Voltage120V

Max continuous16A

Common uses for a 20A breaker

Kitchen countertops, bathrooms, garages, outdoor outlets, laundry. Required by code for kitchens (210.11(C)(1)), bathrooms (210.11(C)(3)), and laundry (210.11(C)(2)).

The 20A breaker is the workhorse of residential wiring. The NEC mandates dedicated 20A circuits for kitchens (at least two per 210.11(C)(1)), bathrooms (210.11(C)(3)), and laundry rooms (210.11(C)(2)). These circuits require 12 AWG copper minimum. 12 AWG is limited to 20A maximum per NEC 240.4(D)(5).

Wire size for a 20A breaker

The wire must have an ampacity that meets or exceeds the breaker rating at the appropriate temperature column. Here are the minimum wire sizes:

Material	Minimum wire	Details
Copper	12 AWG	Standard for residential branch circuits
Aluminum	10 AWG	Common for feeders and above and larger

These sizes assume 75°C termination temperature per NEC 110.14(C), which is the standard for most residential breakers and devices. For long wire runs, check voltage drop - you may need to upsize the wire even though the ampacity is adequate.

Continuous load rule (80% maximum)

For continuous loads - any load expected to run for 3 hours or more - the NEC requires that the load not exceed 80% of the breaker rating (NEC 210.20(A)). On a 20A breaker, the maximum continuous load is 16A.

This is why sizing often seems counterintuitive:

A 16A continuous load (like a space heater) requires a 20A breaker (16 × 1.25 = 20A)
Non-continuous loads can use the full 20A capacity
100% rated breakers exist but are rare in residential panels - assume 80% unless the breaker is specifically listed as 100% rated

Installation notes

Breaker type: A 20A breaker is a single-pole (120V) breaker. It occupies one slot in the panel. The breaker connects one hot conductor to one bus bar in the panel, providing 120V to neutral.

Ground wire: A 20A circuit requires a minimum 12 AWG copper equipment grounding conductor per NEC Table 250.122.

Standard sizes: 20A is a standard breaker size per NEC 240.6(A). Standard residential breaker sizes are: 15, 20, 25, 30, 35, 40, 45, 50, 60, 70, 80, 90, 100, 110, 125, 150, 175, 200. Non-standard sizes should never be used.

Why does my 20A breaker keep tripping?

A 20A breaker trips most often in kitchens when two high-draw appliances run simultaneously on the same circuit. A toaster (10A) and a microwave (12A) on the same 20A circuit will trip every time. This is exactly why the NEC requires at least two separate 20A small-appliance circuits in kitchens. If your kitchen has only one circuit for countertop outlets, it was wired before modern code and should be upgraded. In bathrooms, hair dryers (12-15A) are the most common trip cause - which is why bathrooms require their own dedicated 20A circuit.

Frequently asked questions

What wire size for a 20 amp breaker?

12 AWG copper or 10 AWG aluminum minimum. The wire must have an ampacity at the 75°C column that meets or exceeds 20A. For long runs, you may need to upsize for voltage drop.

What can a 20 amp breaker handle?

Kitchen countertops, bathrooms, garages, outdoor outlets, laundry. For continuous loads (3+ hours), the maximum is 16A (80% of 20A). For non-continuous loads, the full 20A is available.

Can I put a 20A breaker on 12 AWG wire?

Yes - 12 AWG copper is rated for 20A, which matches a 20A breaker.

Is 20A a standard breaker size?

Yes. 20A is a standard breaker size per NEC 240.6(A). It is widely available from all major breaker manufacturers (Square D, Eaton, Siemens, GE). Always use the correct breaker brand for your panel - breakers are not interchangeable between panel brands.

20A wire sizing guide - complete sizing with voltage drop
Ground wire for 20A circuit
12 AWG copper ampacity - derating and conduit fill
12 AWG copper vs aluminum
Single-pole vs double-pole breakers
GFCI vs AFCI protection
NEC Article 240: Overcurrent protection
Ampacity calculator

What to buy

🔌12 AWG WireCopper THHN for 20A circuitCheck prices on Amazon (paid link)⚡20A BreakerStandard overcurrent protectionCheck prices on Amazon (paid link)

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Important: For reference only. Not a substitute for a licensed electrician. Electrical work can cause serious injury, death, fire, or property damage if performed incorrectly. Always hire a licensed electrician for electrical work, especially for service upgrades, panel work, and 240V circuits. Values are derived from NFPA 70 (NEC) for educational purposes. Always verify against your locally adopted NEC edition and amendments - local jurisdictions may enforce stricter requirements. WireRef provides reference information only and is not responsible for work performed based on this content. NEC® is a registered trademark of the National Fire Protection Association. Free NEC access via NFPA · OSHA Electrical Safety · Terms of use.

NEC 2023 references verified April 2026