What Size Wire Do I Need for a 12K Btu Mini-Split Heat Pump

A 12,000 Btu mini-split heat pump is a common choice for heating and cooling a single room or small space, but choosing the correct wire size is critical for safety, efficiency, and code compliance. This guide explains how to determine the right conductor size, factors that affect wire selection, and practical installation and troubleshooting tips.

Component	Typical Amp Draw	Recommended Wire Size (Copper, NM-B or THHN)
Nominal Running Current (RLA)	6–10 A	14 AWG (minimum) for short runs
Maximum Overcurrent/Branch Circuit (MCA/MOP)	12–20 A	12 AWG (common), 10 AWG if long run or high start current

How Mini-Split Electrical Requirements Are Determined

Mini-split manufacturers publish electrical specifications in the unit’s nameplate and manual. Key values include rated voltage, maximum fuse or circuit breaker size, minimum circuit ampacity (MCA), and the rated load amps or running load amperage (RLA). These values form the basis for selecting wire size and overcurrent protection.

The term MCA is used to determine conductor ampacity, while the maximum fuse or circuit breaker size determines the overcurrent device. The installer must follow both the manufacturer’s instructions and the National Electrical Code (NEC) requirements when sizing conductors and protective devices.

Typical Electrical Specs For A 12k Btu Mini-Split

Many 12,000 Btu (12k) single-zone mini-splits operate on 115/120V or 208/230V single-phase circuits. The specific electrical input depends on the model and whether the system is inverter-driven (variable speed) or fixed-speed. Inverter mini-splits commonly have lower running amps and higher starting currents managed by the inverter electronics.

Typical data for a 12k mini-split: rated load amps (RLA) often range from 4–10 A on 230V units, with an MCA of about 10–15 A and a maximum fuse or breaker rating of 15–20 A. For 115/120V models, running amps might be higher, with MCA and breaker sizes adjusted accordingly.

Selecting Conductor Size: NEC And Manufacturer Guidelines

The NEC requires conductors to have an ampacity not less than the unit’s MCA. Conductors must also be sized for voltage drop when the run is long. The conductor insulation type (THHN in conduit or NM-B cable for residential wiring) and installation conditions affect allowable ampacity.

Common practice for 12k mini-splits: use 12 AWG copper for most 230V units with MCA up to 20 A. Use 10 AWG copper for longer runs (to reduce voltage drop) or when the manufacturer lists a higher MCA or maximum breaker size. For 115V models with higher running current, 12 AWG or 10 AWG may be necessary depending on the specified MCA and breaker size.

Example Scenarios And Recommended Wire Sizes

230V Inverter Mini-Split With Low Running Amps

If the unit lists RLA 6 A, MCA 12 A, and maximum fuse 15 A, a 12 AWG copper conductor is appropriate for typical residential installations up to about 50 feet. Install a 15 A or 20 A breaker per manufacturer and local code.

230V Unit With Higher MCA Or Long Run

If the unit lists MCA 16 A or the run exceeds 50–75 feet where voltage drop becomes significant, use 10 AWG copper conductors. A 10 AWG conductor provides greater margin and reduces voltage drop for longer cable runs.

115/120V Unit With Higher Running Current

For a 120V mini-split with RLA 10 A and MCA 14 A, 12 AWG copper is usually acceptable for short runs. If the maximum breaker size is 20 A, ensure conductors and receptacles meet code; consider 10 AWG if the manufacturer or local code dictates.

Voltage Drop Considerations

Voltage drop becomes important when the distance between the breaker panel and the outdoor unit is long. NEC recommends limiting voltage drop to 3% for branch circuits to maintain motor efficiency and longevity.

For a 12k mini-split drawing 10 A on a 230V circuit, the approximate distance where voltage drop becomes a concern is over 50–75 feet for 12 AWG. Upgrading to 10 AWG for runs beyond that length keeps voltage drop within acceptable limits.

Overcurrent Protection: Breakers And Fuses

Overcurrent protection must match the manufacturer’s maximum fuse or circuit breaker rating. The breaker protects wiring and equipment from short circuits and overloads but should not be smaller than the minimum listed by the manufacturer for startup conditions.

Common guidance: use a breaker sized at or below the manufacturer’s maximum but no smaller than required for continuous loads. In many 12k mini-splits the recommended breaker size is 15–20 A on 230V. The installer must attach the correct breaker or fuse type per instructions.

Grounding And Conduit Requirements

All mini-split installations require a grounding conductor sized per NEC Table 250.122 based on the overcurrent device rating. For typical 15–20 A circuits, a 14 AWG or 12 AWG equipment grounding conductor is used with 14 AWG not allowed on 20 A circuits.

If the installation uses conduit, individual THHN conductors are commonly used: two hots and a ground for 240V circuits, or hot, neutral, and ground for 120V systems. For NM-B cable, use appropriate cable gauge (e.g., 12/2 with ground or 10/2 with ground).

Local Code And Permit Considerations

Local electrical codes and utility rules may have additional requirements beyond the NEC or manufacturer instructions. Many jurisdictions require permits and inspections for new HVAC electrical work. Always check with local authorities and obtain necessary permits before installing.

Licensed electricians are often required to perform or inspect HVAC electrical connections. This ensures compliance with local amendments to the NEC, proper breaker sizing, grounding, and adherence to safety practices.

Installation Best Practices

• Always follow the manufacturer’s wiring diagram and nameplate data.
• Use copper conductors unless the manufacturer allows alternatives; aluminum requires larger size and special connections.
• Keep conductor runs as short and direct as possible to minimize voltage drop.
• Install a dedicated circuit for the mini-split; do not share with other high-draw loads.
• Label the breaker at the panel and keep documentation of unit electrical specifications near the panel.

Common Mistakes And Troubleshooting

Undersized wire and improper breaker sizing are common mistakes that can cause nuisance tripping, overheating, and premature compressor damage. Symptoms include frequent breaker trips, reduced performance, and elevated energy use.

If the unit trips the breaker on start, check that the breaker matches the manufacturer’s specified maximum and that wiring is properly sized. Persistent trips may indicate a fault in the outdoor unit or an under-rated breaker.

When To Use A Professional Electrician

Hiring a licensed electrician or certified HVAC technician is recommended when the installer lacks experience with HVAC wiring, when local codes require professional installation, or when the project involves new circuits, panel upgrades, or complex conduit work.

Professionals will verify MCA, select proper wire size, ensure correct overcurrent protection, calculate voltage drop, and pull permits if required. This reduces safety risks and helps guarantee long-term reliability.

Quick Reference Guidelines

For most 12k Btu mini-split heat pumps, the following quick reference applies, but always confirm with the unit’s nameplate and local code: 12 AWG copper for short runs and MCA up to ~15 A, 10 AWG copper for long runs or MCA above ~15 A, and breakers typically 15–20 A as specified by the manufacturer.

Resources And Further Reading

Consult these primary sources when planning an installation: the unit’s installation manual and electrical nameplate, the National Electrical Code (NEC), and local inspection authority guidance. Manufacturer tech support can clarify ambiguous wiring details for specific models.

Using the correct wire size for a 12k mini-split ensures safe operation, efficient performance, and compliance with code. When in doubt, choose a larger conductor and consult a licensed professional to verify the installation.