You're probably looking at a 3.5 ton unit, so you'll be in the 30-40A(10-8AWG) range. It might be worth it to get a few quotes from local HVACcompanies, and see what they want to install. The companies may have a preferred breaker and wire size, so they may want to redo any work you do anyway. electrical - What size breaker and wire do I need for Was this helpful? Wire Type and Sizing Considerations | HVAC Technical Wire Type and Sizing Considerations – When a professional electrician looks at a job to wire a house or a new circuit in any structure the primary consideration in the wiring job is the size and type of wire to be used for the job per the NEC. The same for a plumber when looking at a job the plumber will size the pipes based on the number of How to Size Wire for a Central Air Conditioner | eHow Use the nameplate data from step 1 above to find the correct size wire to conduct power to the central air conditioning unit. Table 310-16 shows that three wires of 6-gauge placed in a conduit will safely conduct 65 amperes of power. The voltage range for this wire falls between 0 volts and 2,000 volts.