What Size Wire For AC Unit: Complete Guide To Selecting The Correct Air Conditioner Wire Gauge

Choosing the right wire size for your air conditioning (AC) unit is crucial for safety, efficiency, and compliance with electrical codes. This detailed guide explores how to determine the appropriate wire gauge for various types of AC units, factoring in amperage, voltage, distance, and code requirements. Using the correct wire size helps prevent overheating and electrical hazards, and ensures your AC runs reliably for years to come.

AC Unit Capacity (Tons/BTU)	Typical Amperage	Recommended Wire Gauge (Copper)	Breaker Size
1.5 Tons (18,000 BTU)	15-20A	12 AWG	20A
2-2.5 Tons (24,000-30,000 BTU)	18-25A	10 AWG	25-30A
3-3.5 Tons (36,000-42,000 BTU)	25-30A	10 AWG	30A
4-5 Tons (48,000-60,000 BTU)	30-40A	8 AWG	40-50A

Factors That Determine Wire Size For AC Units

The correct wire gauge for an AC unit depends on multiple factors. Incorrect sizing can lead to dangerous overheating, system failures, and even void manufacturer warranties or violate electrical codes. Understanding these elements helps homeowners and electricians make safe, code-compliant choices.

Amperage (Current Draw)

The ampacity of your air conditioner’s circuit is the most vital detail. The maximum current draw is specified on the unit’s nameplate as “RLA” (Rated Load Amps) or “MCA” (Minimum Circuit Ampacity). Selecting a wire size that can safely carry at least this current is essential for both performance and safety.

Voltage (120V Vs 240V AC Units)

Most residential central AC units are wired for 240 volts. Smaller window ACs or mini-splits might use 120 volts. Voltage determines wire size requirements: higher voltage can use thinner wires for the same power load, but the amperage and distance must still be considered.

Distance From Breaker To AC Unit (Voltage Drop)

If your air conditioner is over 50 feet from the breaker panel, you may need to upsize the wire due to voltage drop. Excessive voltage drop reduces appliance efficiency and can be risky. Use a voltage drop calculator to verify if upsizing (using a thicker wire) is warranted for runs over 50 feet.

Copper Vs Aluminum Wire

Copper is the industry standard for residential AC wiring because of its superior conductivity. Aluminum wires require upsizing—typically, one gauge size thicker than copper for the same ampacity.

How To Choose The Right Wire Gauge: Step By Step

• Find the AC unit’s Rated Load Amps (RLA) or Minimum Circuit Ampacity (MCA) on the nameplate.
• Check the breaker size recommended by the manufacturer (also listed on the label).
• Refer to National Electrical Code (NEC) tables for minimum wire gauge based on ampacity.
• Account for the type of wire (copper or aluminum) and total wire run distance (adjust for voltage drop if needed).
• Choose wire with insulation rated for outdoor or wet locations if running outside.

National Electrical Code (NEC) Guidelines For AC Unit Wiring

The NEC (National Electrical Code) Article 440 addresses air conditioning and refrigeration equipment wiring. Proper adherence is legally required in most jurisdictions in the United States for new installations and upgrades.

• Wire must be rated for the ampacity of the AC unit and the breaker size.
• Circuit breakers should not exceed the maximum size recommended by the manufacturer.
• Dedicated circuit is required for AC units; don’t share with other appliances.
• Outdoor wire runs must use weather-rated insulation types, like THWN or UF-B.
• Follow local city/county amendments in addition to NEC basics. Some municipalities have stricter rules.

AC Unit Sizes And Wire Gauge Recommendations By Capacity

1.5 Ton To 2 Ton Central Air Conditioners

Most 1.5 or 2 ton residential AC units (18,000–24,000 BTUs) have labeled ampacity (MCA) of 15–20 amps. 12-gauge copper wire (12 AWG) is recommended for circuits fused at 20 amps. If the label recommends a 25 amp breaker, use 10 AWG copper wire.

2.5 Ton To 3.5 Ton AC Units (30,000–42,000 BTU)

Units of this capacity typically list 18 to 25 amps minimum circuit ampacity. Opt for 10 AWG copper wire with a 25 or 30 amp breaker as recommended. If the run is over 75 feet, consider upsizing to 8 AWG for voltage compensation.

4 Ton To 5 Ton Residential Air Conditioners

Bigger systems (4–5 tons; 48,000–60,000 BTU) generally require 30–40 amps. 8 AWG copper wire is typically suitable for up to 40 amps. If your breaker is 50 amps—rare, but possible—consider 6 AWG copper wire.

Window Air Conditioners, Mini-Splits, And Portable ACs

Smaller appliances (5,000–18,000 BTU) usually operate on 15 amp, 120V household circuits. Most will plug into standard 14 AWG or 12 AWG circuits. However, check manufacturer labels for larger window or mini-split models; some require 240V and dedicated 10 AWG wiring.

Common Wire Gauge, Amperage, And Distance Table For AC Units

Wire Gauge (Copper)	Max Amps	Max Recommended Distance (ft) For Full Amps	Typical Breaker Size
14 AWG	15A	50*	15A
12 AWG	20A	60*	20A
10 AWG	30A	80*	30A
8 AWG	40A	100*	40A
6 AWG	55A	125*	55A

*If wiring distance exceeds these recommendations, increase gauge (thicker wire) to reduce voltage drop.

Why Correct AC Wire Sizing Matters

Using the wrong wire size is a common cause of AC electrical failures, system inefficiency, and even fire hazards. Undersized wires can overheat, damage insulation, and eventually cause short circuits. Oversized wires, in contrast, pose no safety threat but do cost more. Getting the wire gauge just right prevents nuisance tripping and prolonged system life.

Signs Of Incorrect AC Wire Sizing

• Frequent breaker tripping during AC operation
• Discolored or warm wire insulation near the breaker or disconnect box
• Reduced AC performance, blowing warm air, or shutting off prematurely
• Visible melting or burning around connections

FAQs About Air Conditioner Wire Sizing

Can I Use A Smaller Wire Than Recommended?

Never use a smaller wire than the minimum required for your air conditioning unit according to code and manufacturer recommendations. Even a small undersizing can lead to catastrophic failure, voided warranty, and insurance liability.

Should The AC Wire Size Match The Breaker Size?

Yes, generally wire size is chosen to match or exceed the breaker size for the maximum amp load. For example, 20 amp breaker requires minimum 12 AWG, 30 amp—10 AWG.

Can I Share The Circuit With Other Appliances?

No. Most codes and manufacturers require that AC units have their own dedicated circuit (not shared with lights, outlets, or other appliances).

How Do I Calculate Voltage Drop For Long Distances?

Voltage drop is a loss of voltage as electrical current flows through a wire. For critical loads such as AC, keep voltage drop below 3%. Use a voltage drop calculator (numerous versions available online) by inputting: Amps, Voltage, Run Length, and Wire Size.

Is It Okay To Oversize The Wire?

Yes, using a larger wire than minimum required is safe. It can reduce voltage drop for long runs and offer extra margin, but does cost a bit more.

Wire Types And Insulation For Outdoor AC Connections

For outdoor or wet locations, standard indoor wire (like NM-B Romex) is not suitable. Instead, use:

• THWN or THHN in conduit for wet/outdoor settings
• UF-B (Underground Feeder) if burying without conduit
• Sunlight-resistant cable if exposed to UV

For most condensers on slabs outside the house, use THWN or THHN wire inside electrical conduit for protection and compliance.

How To Read The AC Unit Nameplate For Electrical Data

Every modern AC unit features a label or nameplate. This is the definitive source for real ampacity and wire sizing information for your specific equipment.

Nameplate Field	Description
RLA (Rated Load Amps)	Typical running amperage of the unit
MCA (Minimum Circuit Ampacity)	Minimum wire and breaker ampacity for safe operation
MOP (Maximum Overcurrent Protection)	Maximum breaker size allowed per unit manufacturer
LRA (Locked Rotor Amps)	Peak starting amperage; for inrush protection, not used for sizing wire

Example: Nameplate Decoding

An AC unit label might read “MCA 20A, MOP 30A”. That means use wire rated for 20 amps minimum (12 AWG copper), and a breaker no larger than 30 amps.

Wire Size For Dual-Component AC Systems

Larger homes often have split AC systems (separate condenser and air handler/furnace with blower). **Each component normally requires its own dedicated circuit and appropriate wire sizing**. Always verify MCA/MOP on both the outdoor and indoor unit labels; don’t assume they match. Often, air handlers use less current and thus smaller wires than condensers.

Common Mistakes When Sizing Wire For Air Conditioners

• Ignoring Manufacturer’s Requirements: Always use the data on the nameplate, not just general rules of thumb.
• Assuming All AC Units Use The Same Amps: Actual amp draw varies by brand, model, and efficiency rating.
• Forgetting To Account For Distance/Voltage Drop: Long wire runs often need up-sizing to avoid losses.
• Using Outdated Electrical Codes: Always reference codes current in your jurisdiction.
• Mixing Copper And Aluminum Wire: Either use one type throughout or use a proper transition connector if you must mix.

Checklist For AC Unit Wire Sizing

• Locate MCA and MOP on the AC unit’s data nameplate
• Determine distance from breaker to unit; consider voltage drop for long runs
• Choose copper or aluminum (copper recommended)
• Refer to NEC ampacity tables for minimum wire gauge
• Select breaker size per manufacturer’s MOP, not exceeding local code
• Use appropriate insulation rating for indoor/outdoor use
• Ensure wire is dedicated—don’t mix loads on the same circuit

Professional Installation Guidance And Permits

In most U.S. cities and counties, a permit and inspection are required for new or replacement AC electrical circuits. Always use licensed professionals for wiring new AC units. They know local codes, can calculate correct wire sizes, and warranty their work to protect your home and investment.

When To Call An Electrician

• You’re unclear about your AC unit’s electrical label
• Running wire longer than 50 feet
• Unsure about outdoor or conduit requirements
• Upgrading old aluminum wiring
• Replacing your electrical panel as part of an HVAC upgrade

Quick Reference Summary: What Size Wire For Common AC Units

• 1.5–2 ton AC (15–20A): 12 AWG copper, 20A breaker
• 2.5–3.5 ton AC (20–30A): 10 AWG copper, 25–30A breaker
• 4–5 ton AC (30–40A): 8 AWG copper, 40A breaker
• Bump up wire size if run exceeds 75 feet
• Always confirm with your AC unit’s nameplate, NEC code, and local amendments