Updated August 2026 · Portlandia Electric Supply · Energy Solutions

Every air conditioner — whether a 3-ton central unit or a 12k BTU mini split — is a continuous load that defines the circuit it sits on. Get the breaker, wire, or disconnect wrong and you get callbacks, failed inspections, or compressor damage. I've seen a $12,000 compressor replacement because the electrician pulled 12 AWG for a 4-ton unit that needed 8 AWG. The wire overheated, the voltage dropped, and the compressor ran starved for 18 months before it seized.

This guide is the electrical side of AC installation: breaker sizing, wire gauge, disconnect placement, and the NEC rules that actually matter in 2026. Portlandia Electric Supply does not stock HVAC equipment — we stock the electrical infrastructure that makes it run: breakers, wire, conduit, disconnects, panels, and transfer switches. If you are sizing the circuit, you are in the right place. For condenser-specific details, see our AC Condenser Electrical Requirements guide. For furnace circuits, see the Furnace Contractor Guide.

This table covers central AC, heat pumps, and mini-splits. Breaker sizes are HACR-rated. Wire is copper THHN/THWN-2 at 75°C.

Key rule: Compressors are motor loads. NEC 440 applies, not the standard branch-circuit sizing in Article 310. Breakers are sized to handle locked-rotor amperage (LRA) on startup — often 5–7× running amps — which is why a 15A-running compressor needs a 30A breaker. I've had apprentices argue that 14 AWG on a 15A breaker should work for a mini split. It won't. The LRA on a 12k BTU mini split can hit 45A for half a second. The HACR breaker handles that. A standard breaker trips.

Article 440 gives two methods for sizing overcurrent protection:

1. Standard method (440.22(A)): Breaker size = 175% of rated-load current (RLA) or branch-circuit selection current (whichever is larger). Round up to the next standard breaker size.
2. Alternate method (440.22(B)): Breaker = 225% of RLA. Only permitted if the breaker does not trip under normal starting — and you must use time-delay fuses or HACR-rated breakers.

*Alternate method limited by nameplate MOP. If MOP is 50A, you cannot use the alternate method result of 51.8A. The nameplate governs.

Practical example: a 3-ton condenser rated 17A RLA / 95A LRA. Standard method: 17A × 1.75 = 29.75A → 30A breaker (HACR-rated). Alternate: 17A × 2.25 = 38.25A → 40A breaker with HACR rating. Most condenser nameplates list "Max Fuse / HACR Breaker" — size to that. Never exceed the nameplate maximum. I had a job in Texas where the nameplate said 35A MOP but the electrician installed a 40A because "that's what we always use on 3-ton units." The inspector caught it. The breaker came out. The drywall patch cost $300.

Do not size wire to the breaker — size to the load with proper derating:

• Attic runs: Ambient can hit 55–65°C. NEC 310.15(B)(2) derates THHN from 75°C ampacity. A 10 AWG THHN rated 35A at 75°C drops to ~28A in a hot attic with three current-carrying conductors. For a 22A compressor in attic conduit, 8 AWG is the safe call. I learned this the hard way on a Houston job in July. The attic was 140°F. The 10 AWG was smoking.
• NM-B (Romex): Limited to 60°C ampacity. 10 AWG NM-B = 30A. For a 25A load, you are at 83% — legal, but hot. Upsize to 8 AWG NM-B or run THHN in conduit. I do not spec NM-B for AC circuits over 20A. The temperature derating kills you.
• Conduit runs to pad-mount: Use THHN/THWN-2 in PVC or EMT. Wet locations require W-rated insulation. EMT is my preference — it provides physical protection and an equipment grounding path if properly bonded.

AC condensers require a disconnect within sight and within 50 feet of the unit:

• Fused disconnect: Provides overcurrent protection if the breaker is remote. Common on commercial and multi-unit installs. I use fused disconnects when the breaker panel is in a mechanical room 80 feet from the condenser.
• Non-fused (pullout) disconnect: Cheaper, lighter, but relies on the upstream breaker. Standard on residential split systems. We sell thousands of these — the 30A non-fused disconnect at $99.99 is our top seller.
• Lockable: Required in many jurisdictions for service access and OSHA lockout/tagout compliance. If the disconnect does not have a hasp, add one. Inspectors check this.

Mini splits are simpler: most inverter-driven units have an integral disconnect or require only a shutoff within sight. Check the installation manual — some brands require a dedicated disconnect; others accept the breaker as the disconnecting means if it's within sight. Mitsubishi, Daikin, and LG all have different requirements. I keep a binder of installation manuals in the truck. Saves callbacks.

A 3-ton central AC on a 30A 240V circuit draws ~7.2kW. On a 200A service, that is fine. On a 100A service already feeding electric range, dryer, and water heater, a NEC 220.83 load calculation often fails. Common fixes:

1. Load-shed device: Automatically drops the water heater or EV charger when the AC starts. Cheaper than a panel upgrade. The Generac Load Control Module handles up to 50A of managed load.
2. Subpanel: Feed a new 60A subpanel from spare lugs or a dual-feed breaker if the main has capacity. We stock Square D and Siemens subpanels for exactly this scenario.
3. Service upgrade to 200A: The right answer if you are also adding a heat pump, EV circuit, or home battery later. A 200A service upgrade runs $2,500–$4,500 in most markets. Factor it into the proposal if the load calc is close.

Mini splits run two cables that must be kept separate:

• Line set (refrigerant): Not electrical — but the condensate pump and line-set penetration need compliance with local mechanical codes.
• Power (high voltage): 240V to the outdoor unit, typically 10–12 AWG depending on amperage and run length. Some small single-zone units run 120V. Always check the nameplate — I've seen 9k BTU units that need 20A 240V circuits because of inverter inrush.
• Control (low voltage): 14–18 AWG two-conductor between indoor head and outdoor condenser. Manufacturer-specified; do not substitute thermostat wire unless the spec allows it. Mitsubishi uses shielded 18/2. LG uses unshielded 16/2. Using the wrong cable can cause communication errors and fault codes.

Max run length: Most manufacturers spec 25–50 feet of line set without refrigerant charge adjustment. Beyond that, wire voltage drop matters too — keep 240V drops under 3%. For a 20A mini split circuit, 10 AWG is good to 80 feet. At 100 feet, upsize to 8 AWG.

In virtually every U.S. jurisdiction, a new AC circuit requires:

• Electrical permit for the new 240V branch circuit.
• HVAC permit for the refrigerant work (if you are the mechanical contractor).
• Inspection of the disconnect location, wire gauge, breaker sizing, and grounding.

Common inspection failures: disconnect not within sight, undersized ground (must match circuit ground, not the smaller control wire), NM-B run underground without conduit, and breaker not HACR-rated. I've also seen failures for missing weep holes in PVC conduit, unsupported EMT sagging more than 1/4 inch per foot, and unlabeled subpanels. The inspectors are not being difficult — they are checking the same items that cause fires and electrocutions.

30–35A HACR-rated. Calculate from RLA × 1.75. If RLA is 17A, 17 × 1.75 = 29.75A → 30A breaker. If the nameplate MOP is 30A, you are at the limit. If MOP is 35A, you have options. Never guess — read the plate.

10 AWG THHN in conduit for standard conditions. 8 AWG if the run is over 75 feet, in a hot attic, or with multiple circuits in one conduit. NM-B is limited to 30A at 60°C and cannot be used outdoors.

Yes. NEC 440.14 applies to all air conditioning equipment. Some mini split manufacturers accept the breaker as the disconnect if it is within sight. Others — especially multi-zone systems — require a dedicated shutoff at the outdoor unit. The installation manual governs.

No. Standard thermal-magnetic breakers trip on compressor LRA. HACR breakers have magnetic trip curves that tolerate the 5–7× inrush for a few cycles. The difference is engineered. The markup is $3–$8 per breaker. Use the right one.

50 feet and within sight. That means the technician standing at the unit can see the disconnect handle and reach it without tools. If a fence blocks the view, move the disconnect or cut a sight window.

NEC 440.6 requires branch-circuit conductors to carry 125% of RLA. A 20A RLA compressor needs 25A conductor ampacity. Since 12 AWG is only 20A at 60°C, you need 10 AWG (35A at 75°C). The 125% rule is why even "small" ACs often need 10 AWG.

No. NM-B is for dry, interior locations. Outdoor condensers are wet locations with physical damage potential. Use THHN/THWN-2 in EMT or PVC. The W rating is for wet — it matters.

RLA is what the compressor draws at full load. MCA is what the wire must handle — RLA × 1.25 plus condenser fan amps. Always size wire to MCA. Size breaker to MOP. Those are the two numbers that matter.

Portlandia Electric Supply stocks the electrical infrastructure AC contractors need: breakers and panels, wire and conduit, AC disconnects, and load management devices. For project-specific quantities and contractor pricing, request a quote — we ship nationwide with same-day fulfillment on orders before 2 PM ET.

• AC Condenser Electrical Requirements — 2026 Contractor Guide
• Furnace Electrical Requirements — 2026 Contractor Guide
• How to Size a Circuit Breaker
• NEC Code Compliance Guide
• Grounding & Bonding Guide
• PES Wire & Cable Collection
• PES Safety & Protection Collection
• PES Electrical Accessories Collection
• Pro Account — Wholesale Pricing
• PowerLink Network — Contractor Program