What Size Breaker for a Mini Split?

Size the breaker to the outdoor unit's nameplate MOP (maximum overcurrent protection, sometimes printed as "Max Fuse/Ckt Bkr"), not to the BTU. Use the largest standard breaker at or below that MOP per NEC 240.6(A) and 440.22, and never above it. Because mini splits are inverter-driven, that MOP often lands on a modest standard breaker even on a large-BTU unit. The one number that sets your breaker is on the data plate, so read it there rather than guessing from the cooling capacity.

Look on the outdoor condenser's nameplate for two figures. The MCA (minimum circuit ampacity) sizes the wire, and the MOP or "maximum fuse/breaker" sizes the overcurrent device. Match the breaker to the MOP and the copper to the MCA at the 75°C column of NEC Table 310.16. If the plate lists a fuse size only, fuses are required (NEC 110.3(B)). Enter those two numbers in the calculator below and it returns the wire, breaker, ground, and voltage drop.

Because a modern mini split uses an inverter compressor, which draws far less current than an old single-stage condenser of the same tonnage. The nameplate MCA and MOP already reflect that low draw, so a unit with a large cooling rating can land on a modest breaker. Always size to the nameplate MCA and MOP, never to the tonnage or BTU: the plate is what the manufacturer and the NEC both point to.

Yes, and for air-conditioning equipment that is correct. NEC 240.4(G) exempts A/C branch circuits from the normal small-conductor rule, so the breaker (sized to the nameplate MOP) can exceed the conductor's ampacity. The breaker only clears short circuits and ground faults there; the compressor's own overload protection guards the wire per NEC 440.52, verified by the equipment listing. Size the wire to the MCA and the breaker to the MOP even when the breaker number is the larger of the two.

Yes. A mini split must be on its own dedicated branch circuit, never shared with another load, and a disconnecting means has to be within sight of the outdoor condenser (NEC 440.14), which is the pull-out disconnect box mounted beside it. The manufacturer's instructions govern the exact wire and breaker (NEC 110.3(B)), so where the manual calls for a larger wire than the bare NEC minimum, install the larger one. The small interconnect cable between the indoor and outdoor units is separate from this branch circuit.

Every calculated figure is re-derived from its locked source before any deploy, backed by 5408 automated checks that also guard where each number comes from. A number that drifts from the cited NEC Article 440 section blocks the ship. This is our own deterministic gate, not a third-party audit. The per-tool receipt is public at https://www.intrysys.com/verified.