What Size Breaker for AC Unit?
Choosing the correct breaker size for your air conditioner prevents nuisance tripping and protects your wiring from overheating. This guide covers breaker sizing by AC tonnage, NEC 440 requirements, and how to read your unit's nameplate data.
How Air Conditioner Breaker Sizing Works
Unlike general-purpose circuits that follow NEC 210, air conditioning and refrigeration equipment is governed by NEC Article 440. This article provides special rules that account for the unique characteristics of compressor-driven equipment, including high startup (locked-rotor) currents and continuous-duty operation.
The key to AC breaker sizing is the unit's nameplate, which lists two critical values:
- MCA (Minimum Circuit Ampacity): The minimum ampacity for the branch circuit conductors. The wire must be rated for at least this value.
- MOCP (Maximum Overcurrent Protection): The largest breaker permitted for the circuit. The breaker must not exceed this value.
The breaker can be any standard size between MCA and MOCP. The wire must be sized for MCA or larger.
AC Breaker Size by Tonnage (General Guidelines)
The table below shows typical breaker sizes for common residential central AC units at 240V. These are general guidelines — always verify against your unit's nameplate.
| AC Size (Tons) | Cooling Capacity (BTU/h) | Typical Running Amps | Recommended Breaker | Minimum Wire Gauge (Copper) |
|---|---|---|---|---|
| 1.5 Ton | 18,000 | 10–12A | 20A | 12 AWG |
| 2 Ton | 24,000 | 12–15A | 25A | 10 AWG |
| 2.5 Ton | 30,000 | 14–18A | 30A | 10 AWG |
| 3 Ton | 36,000 | 16–20A | 35A | 8 AWG |
| 3.5 Ton | 42,000 | 18–24A | 40A | 8 AWG |
| 4 Ton | 48,000 | 20–28A | 45A | 6 AWG |
| 5 Ton | 60,000 | 25–35A | 50A | 6 AWG |
Wire gauge based on 60°C ampacity per NEC Table 310.16. Actual wire gauge depends on distance, ambient temperature, and conduit fill.
Understanding NEC Article 440
NEC 440 is specifically designed for air conditioning, refrigeration, and heat pump equipment. It modifies the general rules in several important ways:
- NEC 440.6: The rated-load current and branch circuit selection current on the nameplate are used for sizing, not the general load calculation methods.
- NEC 440.22(A): The branch circuit overcurrent device (breaker) must not exceed the value listed on the equipment nameplate as MOCP.
- NEC 440.22(B): For hermetic refrigerant motor-compressors, the breaker can be set at a value that allows the compressor to start without tripping.
- NEC 440.32: Single motor-compressor equipment must be on a dedicated branch circuit.
These provisions recognize that compressors draw significantly more current during startup (locked-rotor amperage) than during normal operation, and the breaker must tolerate these brief surges.
How to Read Your AC Nameplate
Every outdoor condensing unit has a metal nameplate (usually on the side of the unit) that lists electrical specifications. Here's what to look for:
| Nameplate Field | What It Means | How to Use It |
|---|---|---|
| Voltage | Operating voltage (usually 208/230V or 240V) | Must match your panel voltage |
| Phase | Single-phase or three-phase | Residential is almost always single-phase |
| RLA (Rated Load Amps) | Normal running current | Used for wire sizing calculations |
| LRA (Locked-Rotor Amps) | Startup inrush current | Used by engineers to check voltage drop |
| MCA | Minimum circuit ampacity | Wire must be rated ≥ MCA |
| MOCP | Maximum overcurrent protection | Breaker must be ≤ MOCP |
Wire Size for AC Circuits
The wire gauge for an AC circuit is determined by the MCA value on the nameplate, not the tonnage chart. General guidelines:
- MCA ≤ 15A: 14 AWG copper
- MCA ≤ 20A: 12 AWG copper
- MCA ≤ 30A: 10 AWG copper
- MCA ≤ 40A: 8 AWG copper
- MCA ≤ 55A: 6 AWG copper
For long runs (over 100 feet), consider upsizing the wire to compensate for voltage drop. A voltage drop exceeding 3% on a dedicated AC circuit can reduce compressor efficiency and lifespan.
Mini-Split vs. Central AC Breaker Sizing
Mini-split heat pumps and ductless AC units have different electrical characteristics than central systems:
- Mini-splits are typically more efficient and may require smaller breakers. A 1.5-ton mini-split might need only a 15A breaker, while a 1.5-ton central unit typically needs 20A.
- Multi-zone mini-splits (one outdoor unit, multiple indoor units) may require larger breakers comparable to central systems.
- Always check the nameplate — mini-split manufacturers vary widely in their electrical specifications.
Common Questions About AC Breakers
Can I Replace a 30A Breaker with a 40A for My AC?
Only if the nameplate MOCP is 40A or higher. Installing a breaker larger than the listed MOCP violates NEC 440.22 and creates a fire hazard. You cannot simply increase the breaker to prevent tripping — if the breaker trips, there may be a compressor problem, loose connection, or incorrect sizing.
Why Does My AC Breaker Keep Tripping?
Common causes include:
- Dirty condenser coils causing the compressor to overwork
- Low refrigerant charge (often due to a leak)
- Failing compressor with high amperage draw
- Loose or corroded electrical connections
- Undersized wire causing voltage drop
- Wrong breaker size (always verify against nameplate)
Do I Need a Disconnect for My AC?
Yes. NEC 440.14 requires a disconnecting means within sight of the outdoor unit. This is typically a non-fused pull-out disconnect rated for the circuit amperage. It allows maintenance personnel to safely de-energize the unit.
Frequently Asked Questions
What size breaker do I need for a 3-ton AC unit?
A typical 3-ton air conditioner requires a 35-amp breaker on a 240V dedicated circuit. This is a general guideline — always check the unit nameplate for exact MCA and MOCP ratings.
Why do AC units need HACR-rated breakers?
AC compressors have high inrush currents at startup. HACR-rated breakers are tested per UL 489 to handle these momentary surges without nuisance tripping, while still protecting the circuit during sustained overloads.
What is MCA and MOCP on an AC nameplate?
MCA (Minimum Circuit Ampacity) is the minimum wire ampacity required. MOCP (Maximum Overcurrent Protection) is the largest breaker allowed. The wire must be rated for at least MCA, and the breaker must not exceed MOCP.
Can I use a smaller breaker than recommended for my AC?
You can use a breaker rated between the MCA and MOCP values on the nameplate. Using a breaker smaller than MCA will cause nuisance tripping. Using one larger than MOCP violates NEC 440.
Does a mini-split need a different breaker size than a central AC?
Yes. Mini-split units typically have lower electrical requirements than central AC systems of equivalent tonnage. Always refer to the manufacturer nameplate for mini-split breaker sizing, as MCA and MOCP values vary significantly by model.