What Size Wire for a Mini Split?

Size the wire to the outdoor unit's nameplate MCA (minimum circuit ampacity), not to the BTU rating. Mini splits are inverter-driven and efficient, so their MCA is often lower than a conventional AC of the same capacity. As a rough guide, a 9,000-12,000 BTU (3/4 to 1 ton) unit runs an MCA around 10-15A and takes #14 copper on a 15-20A breaker; an 18,000-24,000 BTU unit runs 15-22A and needs #12 or #10. Multi-zone condensers run higher. Always read the data plate: the MCA and the 'maximum fuse/breaker' are printed there.

Use a standard breaker at or below the nameplate 'maximum overcurrent protection' (MOCP, sometimes labeled max fuse/breaker). For most single-zone mini splits that is a 15A, 20A, or 25-30A double-pole breaker at 208-240V. Do not exceed the nameplate maximum, and do not size the breaker to the BTU: a 12,000 BTU unit is commonly a 15A or 20A circuit despite the large cooling number.

Many smaller mini splits can. A 9,000-12,000 BTU single-zone unit often has an MCA under 15A and a max breaker of 15A or 20A, so a dedicated 15A (#14) or 20A (#12) 208-240V circuit is typical. Confirm on the nameplate: if the MCA exceeds 15A or the max breaker is higher, step up. Larger and multi-zone units need 20-30A circuits.

Yes. The outdoor condenser must be on its own dedicated branch circuit (NEC 440.6/440.31), and a disconnecting means must be within sight of and readily accessible to it (NEC 440.14), which is the pull-out disconnect box mounted near the unit. The small interconnect cable between the indoor and outdoor units is separate from this branch circuit and is sized per the manufacturer.

The method is identical (size to nameplate MCA and MOCP per NEC Article 440), but the numbers differ: an inverter mini split usually draws less than a conventional single-stage AC of the same tonnage, so a 1-ton mini split may sit on a 15A circuit while a 1-ton conventional condenser might want a 20-30A circuit. Always use each unit's own nameplate.