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It is not unheard of to have different contractors tell you different size wires- some will go for the minimum, some for future proofing. My apologies for misreading your question. You should ask the contractors about that.Įdit: I see you have called a professional. Not sure why different electricians are wanting to go with different things, maybe they're trying to future-proof, or they're just going to use what they have in stock. Most of them are rated at 30 or 60 amps, which is more than what you need, and would be fine. If you have the circuit breaker at the panel, you could use a non-fused disconnect. If you go smaller then 20 amp, you will experience nuisance tripping, and you are not allowed to go larger than 25 amps. That breaker would normally be too large for 12 gauge wire, it's only allowed in a case like this where the A/C unit is rated as such. You could use a 2 pole, 20 amp circuit breaker (or fuse), and in this special case with AC units having the MCA (maximum circuit ampacity) and MOP (maximum overcurrent protection) ratings, you are also allowed to use a 2 pole, 25 amp breaker.
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You could go with larger wire (10 gauge), but not smaller (14 gauge). Assuming you're in the US, the minimum you would need based on the nameplate info would be 12/2+ground (12 gauge wire with 2 conductors and a ground wire).