What Size Breaker for an Air Conditioner?

Size an AC breaker from the nameplate, not a rule of thumb: use the Minimum Circuit Ampacity (MCA) for wire size and the Max Overcurrent Protection (MOP/MOCP) for the breaker.

MCA and MOP: the two numbers that size an AC circuit

Every central air conditioner and heat pump condenser carries a data nameplate with two ratings that replace all rules of thumb:

MCA (Minimum Circuit Ampacity) — the minimum ampacity the circuit conductors must have. The MCA sets the wire size. The manufacturer has already applied the NEC 440.32 factor (125% of the compressor rated-load current plus other motor loads), so you do not add another 125%.
MOP or MOCP (Maximum Overcurrent Protection) — the largest breaker or fuse permitted. The MOP sets the breaker size, per NEC 440.22.

The counterintuitive part: on an AC circuit the breaker is allowed to be larger than the wire's normal ampacity rating. A nameplate might read MCA 19.9 A / MOP 35 A — meaning 12 AWG copper conductors (rated 20 A) protected by a 35-amp breaker. That is code-compliant because the breaker on a hermetic compressor circuit exists to handle short circuits and ground faults while riding through motor starting inrush; running overload protection is built into the compressor itself. This is defined in NEC Article 440, and it is why copying breaker-to-wire pairings from receptacle circuits gives the wrong answer for air conditioners.

The sizing procedure is therefore two independent lookups: pick conductors with ampacity ≥ MCA, and pick a breaker ≤ MOP (and large enough to start the unit — in practice, the MOP value or the nameplate's stated range).

Typical breaker sizes by AC tonnage

The table below shows typical MCA and MOP ranges for residential 240-volt central air condensers by tonnage. These are typical values only — always follow the nameplate on your specific unit; SEER rating, compressor type, and brand shift the numbers significantly.

Typical central AC circuit sizes by tonnage (240 V — nameplate always governs)
AC size	Cooling BTU	Typical MCA	Typical MOP (breaker)	Typical copper wire
1.5 ton	18,000	10-14 A	15-20 A double-pole	14-12 AWG
2 ton	24,000	12-17 A	20-25 A double-pole	14-12 AWG
2.5 ton	30,000	15-20 A	25-30 A double-pole	12-10 AWG
3 ton	36,000	18-23 A	30-35 A double-pole	12-10 AWG
3.5 ton	42,000	21-27 A	35-40 A double-pole	10 AWG
4 ton	48,000	23-31 A	40-45 A double-pole	10-8 AWG
5 ton	60,000	26-34 A	45-60 A double-pole	8 AWG

As working orientation: a 2-ton condenser commonly lands on a 20-25 A breaker, a 3-ton on a 30-35 A breaker, and a 4-ton on a 40-45 A breaker — but a high-SEER 3-ton unit can legitimately carry a 25 A MOP while an older builder-grade one carries 40 A. Read the plate.

Window units and mini-splits

Most window air conditioners up to about 12,000 BTU run on an ordinary 120-volt, 15-amp circuit with a standard 5-15 plug; NEC 440.62 limits a cord-connected room AC to 80% of the circuit rating when the circuit also serves other loads, and 50% where lighting shares it — so large window units usually want a dedicated circuit. Big window and through-wall units (15,000+ BTU) step up to 240 volts on a 15- or 20-amp double-pole circuit with a 6-15 or 6-20 plug.

Ductless mini-splits are sized exactly like central units — from the nameplate MCA and MOP. Typical single-zone residential mini-splits run 240 volts with an MCA of 10 to 20 amps and an MOP of 15 to 25 amps, wired through an outdoor disconnect. Multi-zone units go higher.

HACR breakers

Air conditioning circuits use HACR-rated breakers (Heating, Air Conditioning, Refrigeration) — a listing that confirms the breaker tolerates grouped motor starting currents. Practically all modern residential breakers from major brands are HACR-rated and marked as such on the label, so this is a check-the-marking item rather than a special purchase; on older panels, verify the marking before reusing an existing breaker.

Common AC breaker mistakes

Sizing wire from the breaker. On AC circuits the wire follows MCA, not the breaker. A 35 A breaker over 12 AWG wire can be correct here — and 10 AWG wire under a 60 A breaker can be wrong.
Exceeding the MOP because the breaker "keeps tripping". Nuisance tripping means a failing capacitor, dirty coils, low refrigerant, or a tired compressor — not an undersized breaker. Installing a breaker above the nameplate MOP violates NEC 440.22 and removes short-circuit protection margin.
Ignoring the air handler. The indoor unit (blower, and especially electric resistance backup heat strips) is a separate circuit with its own nameplate MCA/MOP; heat strips commonly need 30-60 A more than the condenser.

Safety first

This page is educational reference material. AC circuits involve 240 volts, motor loads, outdoor disconnects, and Article 440 rules that differ from ordinary branch circuits. Fixed electrical installation work must be carried out by a licensed electrician in accordance with the applicable local wiring code (e.g. NEC/NFPA 70, BS 7671, AS/NZS 3000, IEC 60364), and HVAC circuit changes typically require a permit.

Frequently asked questions

What size breaker do I need for a 3-ton AC unit?

Typically a 30- to 35-amp, 240-volt double-pole breaker on 12 to 10 AWG copper — but the only correct answer is on the condenser nameplate: wire to the MCA (Minimum Circuit Ampacity) and breaker at or below the MOP (Maximum Overcurrent Protection). A high-efficiency 3-ton unit can carry a lower MOP than an older one.

What does MCA mean on an air conditioner nameplate?

Minimum Circuit Ampacity — the minimum current rating the circuit conductors must have. It already includes the NEC 440.32 factor of 125% of the compressor rated-load current, so you size the wire directly to the MCA without adding another 125%.

What is MOP or MOCP on an AC unit?

Maximum Overcurrent Protection — the largest breaker or fuse the manufacturer permits for the unit, per NEC 440.22. Install a breaker at or below the MOP. A breaker above the MOP is a code violation even if the wire could carry it.

Can the AC breaker be bigger than the wire rating?

Yes, on hermetic compressor circuits this is normal and code-compliant under NEC Article 440. For example, MCA 19.9 A / MOP 35 A means 12 AWG wire on a 35-amp breaker. The oversized breaker rides through motor starting inrush; the compressor has its own built-in overload protection.

What size breaker does a window air conditioner need?

Most window units up to about 12,000 BTU plug into a standard 120-volt, 15-amp circuit. Larger 15,000+ BTU units typically require 240 volts on a 15- or 20-amp double-pole circuit with a NEMA 6-15 or 6-20 receptacle. NEC 440.62 limits a room AC to 80% of the circuit rating on a shared circuit.

What is a HACR breaker and do I need one for AC?

HACR stands for Heating, Air Conditioning, Refrigeration — a breaker listing for circuits with grouped motor loads like compressors and fans. AC equipment specifies HACR-rated protection, and virtually all modern residential breakers carry the HACR marking; verify the label on older panels.

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Last verified: 2026-07-10